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Guide to the GEOLOGY of LONDON and NEIGHBOURHOOD. By W. WHITAKER. 6th Ed. Is. 4 - - FOLKESTONE and BYE. By F. DREW. It. 34 - - - PARTS of WILTS, and GLOUCESTERSHIRE. By A. C. RAMSAY, W. T. AVELINE, and E. HULL. 8rf. 44 - - - CHELTENHAM. By E. HULL. 2s. Gd. 45 - - - BANBURY, WOODSTOCK, and BUCKINGHAM. By A. H. GREEN. 2s. 45 SW - - WOODSTOCK. By E. HULL. Is. 47 - - - N.\\ . ESSEX & N.E. HERTS. l?y W. WHITAKER, W. H. PENNING, W. H. DALTON, & F. J. BENNETT. 48 SW - - COLCHESTER. By W. H. DALTON. Is. Gd. 48 SB - - EASTERN END of ESSEX (WALTON NAZE and HARWICH). By W. WHITAKER. !'n Granit gebunden Mineral - Neubildungen." Zeitschrift fur praktische Geolojie, Dec. 1894, p. 458, " Beitrage zur genetischen Classification der durch magmatische Differentia- tionsprocesse und der durch Pneumatolyse entstanden Erzvorkommen." Ibid. April, 1895, p. 145. " Problems in the Geology of Ore-deposits." Trans. American Institute, Mining Engineers, vol. xxxi. (1902), p. 125. f" Erlauterungen zur geologischen Specialkarte des Konigreichs Sachsen. Section Altenberg-ZinnwiUi." Sheet 119. Leipzig: 1890, p. 66. Also: " Der Altenberg-Graupener Zinnerzlagerstattendistrict." Zeitsch. f. prakt. Geologic, Aug. 1894, p. 313. J " Lehrbuch der chemischen und physikalischen Geologic," 2nd Ed., vol. iii. (1866), p. 811. TIN-ORES. 13 that it is slightly soluble even in distilled water at 80C., whilst the solubility is increased by the presence of sodium fluoride, though not by sodium chloride.* Its occurrence in the waters of certain hot springs is inferred from its presence in deposits of siliceous sinter. Thus, M. Errington de la Croix obtained from a warm spring at Ajer Panas, in Selangor, a deposit consisting mainly of opaline silica like geyserite, which was found, on analysis by Prof. Stanislas Meunier, to contain 5 per cent, of stannic oxide.")* Here, then, is an example of the contemporaneous formation of a tin-bearing deposit. According to Mr. J. H. Collins, the antlers of the red deer, formerly found rather abundantly in the tin-bearing gravels worked in the Carnon and Pentuan valleys, were partially mineralised with cassit- erite. His analysis of a specimen in the museum of the Royal Geological Society of Cornwall showed the presence of 2 -6 per cent, of stannic oxide. J Mr. R. Q. Crouch, describing a certain specimen, says " the whole horn had undergone a change into tin ore." But possibly this may not imply solution of the tinstone. In certain Cornish mines there have occasionally been found con- glomerates and breccias, consisting of fragments of rock broken from the walls of the lode and rolled pebbles washed into the fissure cemented together with cassiterite and other minerals, which have probably been deposited from circulating waters. No. 49 is a speci- men of the famous conglomerate from the Relistian mine, in Gwinear, described nearly a century ago by Mr. Joseph Carne,|| in which cassiterite, in a crystallised condition, forms part of the cementing medium. In a brecciated lode occurring at New Rosewarne mine, and described by Sir C. Le Neve Foster, the agglutinating minerals included quartz, cassiterite, mispickel, chlorite and pearl-spar. Pseudomorphs or those minerals which by chemical or mech- anical alteration assume the crystal forms of other species, so that their substance and structure bear no necessary relation to external form are in many cases highly suggestive in discussing the origin of minerals. Nos. 47 and 48 are examples of the well-known pseudo- morphs of cassiterite after felspar from Wheal Coates,U an old tin * Journ. Chem. Soc., vol. Iviii (1890), p. 1070. Min. Mit., Ed. xi (1890), p. 325. f " Examen chimique d'eaux minerales provenant de Malaisie ; mineral d'etain de formation actuelle." Comptes Rendus (27th May, 1890), tome ex., p. 1083. % " Note on the occurrence of stanniferous Deerhorns in the tin-gravels of Cornwall." Trans. Roy. Geol. Soc. Corn., vol. x. (1887), p. 98. " Notice of the occurrence of the Horns and Bones of several species of Deer in the Tin Works of Cornwall." By Richard Q. Crouch, Esq. Trans. Roy. Geol. Soc. Corn., vol. vii. (1865), p. 185. || " An account of the Relistian Mine." Phil. Trans., vol. for 1807, p. 293. T[ The word Wheat, denoting a mine, is the usual form in which the old Cornish word Hud is now written. The late Mr. Robert Hunt tried in vain to revive the original form. Writing in 1884 he says : " I have constantly employed, since 1847, the term 'Huel ' which is undoubtedly the ancient Cornish term signifying a mine or mineral work but the corruption ' Wheal ' is so undeviatingly used by all, that there is no reason why I should any longer endeavour to bring the older term into use again." " British Mining." By Robert Hunt, F.R.S. '1884), p. 190. 14 MINERALS OP CORNWALL AND DEVON. mine near St. Agnes, where they occurred at one time in great abundance. The crystals present mostly the characteristic form of Carlsbad twins of orthoclase* ; but while the shape has been faith- fully preserved the felspathic matter itself has disappeared. The replacing material consists largely of cassiterite, usually a granular mixture of cassiterite and quartz. The lode which yielded these remarkable pseudomorphs, which are said to have " occurred in millions," was in a soft decomposed granite, or perhaps an elvan, and contained so much sandy matter that it has been called a " sand lode."f Similar pseudomorphs have been found, though but rarely, at other localities in Cornwall, as at Carn Brea and at Balleswidden, near St. Just. It seems probable that they were formed by the pneumatolytic alteration of a porphyritic rock, after its consolida- tion but while still in a heated condition. On the other hand, it was contended by Bischof that ordinary carbonated waters, coursing through tin-bearing rocks, might be competent to dissolve felspar and to deposit tinstone in its place. The presence of tin has been recorded in certain rock -forming minerals, notably in zinnwaldite, a lithia-mica, where it probably exists as microscopic inclusions of cassiterite. It has even been suggested that in some silicates tin may partially replace silicon, that tin dioxide may play the part of silicon dioxide. It was the presence of the heavy metals in many rock-forming silicates that led the late Prof. F. Sandberger to his well known views on the origin of mineral veins by a process of lateral secretion.% According to this hypo- thesis, the neighbouring rocks are to be regarded as the primitive source of the ores, the contents of a mineral vein having been leached out of the surrounding " country." Although this view received much support, it also encountered much opposition, especially from the late Prof. A. Stelzner, of Frei- berg. Admitting that the heavy metals of the ores really exist in some of the minerals of the neighbouring rocks of which, indeed, there seems no doubt it remains a matter of discussion as to the direction the migration may have taken place ; whether the tin in the rock has escaped from the vein, or the tin in the vein been drawn from the surrounding rock. Probably there is some truth in both views. The formation of a mineral-vein is usually so complex a process that there is room for several explanations applicable to different phases of its develop- ment. If the tin-ore was originally derived from deep-seated sources by magmatic extraction, it may subsequently have become distributed * See Laspeyres, Zeits. f. Kryst., vol. i. (1877), p. 344 ; Kohlmann, ibid., vol. xxiv. (1895), p. 355. " Carlsbad twins " are so called because characteristi- cally seen in the orthoclase-felspar of the Carlsbad granite. t In some of the Wheal Coates pseudomorphs, the felspar has been replaced by kaolin and secondary mica, as seen in No. 48, and in certain specimens in the Case of pseudomorphs and others in the Horse-shoe Case. For British pseudomorphs generally see Prof. Miers in Min. Mag., vol. xi. (1897), p. 263. 1 " Untersuchungen iiber Erzgange." Von Fridolin Sandberger. Wies- baden. 1882. CASSITERITE. 15 by solution ; whilst ore disseminated through a rock as an impregna- tion may have been dissolved out, transported to a greater or less distance, and segregated locally. The plane of weakness in a rock, represented by a vein, has in most cases been opened again and again, and has been the scene at different stages of very varied activities. Dr. Flett has recently shown how complicated must have been the history of certain brecciated veinstones in Cornwall.* Cassiterite. (Nos. I to 67.) The specimens numbered 1 to 67, exhibited in the first division of Case 1, are (with the exception of No. 46) examples of Cornish Cassiterite or tinstone. The crystals from Cornwall are usually small, but some of exceptional size are here exhibited, and others will be found among the British ores in Wall-cases 7 and 8. Cassiterite crystallises in the tetragonal system, termed by some writers the pyramidal, dimetric or quadratic system. f The specimen No. 1 shows short four- sided prisms, each terminated by a four-faced pyramid ; but crystals of such simple type are not common. Many, if not most, of the crystals exhibited in this case are twinned, or macled, sometimes exhibiting geniculate or knee-shaped structures. Small paper arrows on No. 6 point to the re-entrant angles so characteristic of twinned crystals, and many similar, if less conspicuous, angles may be observed on other specimens. J Nearly a century ago, a large series of fine crystals of Cornish tin- stone was examined by William Phillips, and described and figured by him in an early volume of the " Transactions of the Geological Society of London. " His observations enabled him to trace a local distribution of particular types of crystals. The colour of cassiterite, as shown by the specimens in this case, is frequently a rich chestnut-brown, passing into a brilliant black. It is generally said that the dark colour is due to the presence of ferric oxide. Zonal colouration is sometimes seen in microscopic sections of crystals of cassiterite. In Nos. 19 and 20 the crystals are trans- lucent and of a red colour, rather like some kinds of ferruginous quartz; but such crystals are rare. A yellowish brown tinstone, somewhat * Geol. Surv. Summary of Progress for 1902 (1903), p. 154. t Crystals are classified, according to their geometrical and physical char- acters, in large groups called systems. Within thesa systems there are smaller groups, based on certain types of symmetry, called classes. Six natural systems are recognised, and thirty-two classes are possible. For modern views on crystals the student may consult Prof. N. Story-Maskelyne's " Crystallo- graphy " (Oxford: 1895), and Prof. W. J. Lewis's "Treatise on Crystallo- graphy " (Cambridge: 1899). See also Prof. Miers's "Mineralogy'^ (London: 1902), J A re-entrant angle is one exceeding 180, or greater than two right angles. uv A Description of the Oxyd of Tin." By William Phillips, Trans. Geol. Soc., vol. ii. (1814), 336. Cornish cassiterite has since been the subject of crystallographh study by Prof. Becke (Min. Mit., 1877, p. 243), Dr. Kohlmann (ZeUs. /. Kryst., vol. xxiv., 1895, p. 350), and others. 16 MINERALS OP CORNWALL AND DKVON. translucent, is called rosin-tin. In connection with the colour of cassiterite, attention may be directed to some white tinstone from the Malay Peninsula presented by Cecil Wray, Esq., and exhibited in Wall-case 40 ; whilst among the Australian minerals in Wall-case 38 will be found some yellow, brown, and red cassiterite, so trans- parent as to be cut into gem-stones, which display diamond-like brilliancy. The adamantine lustre of cassiterite is rather character- istic, and the eye will be attracted by the splendent faces of many of the Cornish crystals. The variety of cassiterite known as sparable tin is represented by Nos. 21 to 32. This variety occurs in sharply-pointed crystals due to a large development of the ditetragonal, or eight-sided pyramid, associated with a slender prism striated vertically. According to Mr. K. H. Solly who has studied this type,* it occurs chiefly in the Camborne district, always in close proximity to an elvan, and invari- ably accompanied by chlorite or " peach." The common name is said to have been suggested by the resemblance of the sharp elongated crystals to the sparable nails used by cobblers, the term " sparable " itself being, perhaps, a corruption of " sparrow- bill," in allusion to the shape. Other trivial names are tooth-tin, referring to the acute pyramidal terminations (No. 23), and needle-tin, applied to the very slender crystals (Nos. 27, 31, etc.). The fibrous variety of cassiterite known as wood-tin is represented by a series of specimens (Nos. 33 to 40.) This mineral was originally found in the form of rolled fragments in the old Cornish workings for stream-tin, and for a long time was known only in this detrital form. Examples of such water-worn fragments, exhibited in the tray No. 34, show the characteristic fibrous structure, the hair- brown colour, and the dull lustre of this variety. Many of these pieces resemble, except in density, the fibrous oxide of iron called u wood-iron ore " ; and old writers, struck with the resemblance of the wood-tin to fibrous hrematite, termed it tin-hcematite. The small pebbles of concretionary tinstone t No. 43, present a zonal structure, similar to that of an agate, and suggest gradual formation by a sequence of deposits. The agatiform appearance is well seen in the large pebble with a dimpled surface, each pit here representing the position of a former nucleus surrounded by successive rings. Some of the small pebbles in No. 44 show the botryoidal shape of the concretions. In the large water-worn fragment, No. 41, the wood-tin is associated with vein-quartz, suggesting the source of the mineral. Wood-tin in the matrix is of exceptional occurrence, but several fine examples are here shown. The specimens in Tray No. 33, from the Prideaux Wood mine, near Liskeard, exhibit wedge-shaped segments of globular concretions, composed of radiating fibres with concentric bands of pale and dark brown tints. The mineral is extremely brittle, breaking in the direction of the fibres. These * " Cassiterite, ' Sparable Tin,' from Cornwall." By R. H. Solly, M.A. Mineralogical Magazine, vol. ix. (1891), p. 199. CA.SSITER1TE. 17 specimens were obtained from a lode of copper-ore, and are loosely embedded in a brecciated matrix composed of quartz, chlorite, iron- pyrites, copper pyrites, and brown oxide of iron.* In the specimen No. 37, from Fowey Consols, small fibrous con- cretions of pale brown wood-tin are embedded in a " peachy " vein- stone. No. 38 shows a mass of cassiterite enclosing numerous small globular concretions of wood-tin. Each globule exhibits on the fractured surface a pale brown nucleus, surrounded by an inner ring and an outer zone of dark divergent fibres. In this specimen the cassiterite is associated with lamellar carbonate of lime, or Schiefer spar, an association which is quite exceptional in Cornwall. The specimen probably came from the Garth Mine, near Penzance, and bears Heuland's label, dated 1839, describing it as unique. Pebbles showing the small rings of wood-tin, in varying shades of brown, as seen in some of the pieces in the Tray No. 44, are known as toads' -eye tin. In the interesting specimens Nos. 35 and 36, believed to be from the Sancreed Mine, the wood-tin occurs in brown zones investing quartz. The fracture of No. 35 has disclosed a hexagonal pyramid of quartz, with pitted surface, completely surrounded by dark brown fibrous tinstone, crystallised on the outside of the deposit. The botryoidal form of the free surface of the wood-tin is well seen on No. 36. The matrix seems to be an altered granitic rock, with quartz, pink orthoclase and much cassiterite. No 40 is an example of the nodular masses of tinstone with fibrous structure, which occurred rather plentifully at one time at Great Wheal Vor Mine, near Helston.f At this mine wood-tin was found as isolated masses, as scattered grains and as small veins, at a depth of about 200 fathoms. The specimen exhibited is not ordinary wood-tin, but fibrous cassiterite of nearly black colour, some of the fibres, however, being brown, slightly translucent and resinous. It has been pointed out by Mr. J. H. Collins, that ancient ingots of metallic tin, such as those known in Cornwall as "Jews' House Tin," may become coated naturally with an incrustation of tin dioxide, having microscopically a fibro -radiate and concentric structure, very similar to that of wood-tin. J By the disintegration of tin-lodes and other stanniferous deposits, the cassiterite may be set free, and after transport by running water be deposited as pebbles, gravel or even fine sand. This is the stream-tin, which was formerly found in superficial deposits in many * The varieties of wood-tin are fully described by Mr. J. H. Collins, F.G.S., in the second part of his paper " On Cornish Tin-stones and Tin-capels." Miner alogical Magazine, vol. iv. (1882) p. 1 (first paper), p. 103 (second paper), and vol. v. (1884), p. 121 (third paper). Reprinted, with additions and cor- rections, and with separate pagination. Truro : 1888. t " On the occurrence of wood -tin at the Great Wheal Vor Mines." By G. M. Henty. Rep. Miners' Assoc. Cornwall find Devon, 1867, p. 55. " On the occurrence of wood-tin ore in the Wheal Metal Lode at Wheal Vor ia Breage." By William Argall. Journ. E. Inst. Cornwall, vol. iv. p. 255. + Min. Mag., vol. iv. (1882), p. Ill, 7882. C 18 MINERALS OF CORNWALL AND DE^ON. parts of Cornwall.* Several examples of this detrital tin ore are here exhibited (Nos. 41 to 45). No. 41 is a large water- worn fragment from a tin lode, showing the cassiterite attached to vein quartz ; No. 42 is a tray of rather large well-rounded pebbles ; Nos. 43 and 44 are trays of small fragments of stream-tin including pebbles of agatiform cassiterite and toad's-eye tin ; No. 45 is an example of the fine sandy alluvial tin. In the sand the cassiterite is associated with other hard and dense minerals, such as magnetite, ilmenite and native gold, derived from the disintegration of the tin- bearing rocks. Probably the alluvial deposits of tin-ore in Cornwall attracted attention in prehistoric times, and were worked as a source of the metal before the veins themselves had been attacked by the miner. All the old tin stream-works are now practically exhausted, though certain patches of " tin-ground " continued to be worked until quite a recent period. The tin-streaming carried on at the present time along the Red River, between the parishes of Camborne and Illogan, is confined to washing the tailings, or slimes, allowed to run to waste from the dressing-floors of modern mines. Borings made a few years ago in the lower part of the Red River valley, in quest of true tin- gravels which might have been neglected by the old workers in the district, proved the existence of undisturbed stanniferous alluvium, though no payable patches were detected.f Gold was found in most of the old stream-works, and the tinners were in the habit of collecting the glittering grains and preserving them in quills. Occasionally, though very rarely, a comparatively large nugget was discovered. One of these exceptional pieces is here exhibited (No. 46). This specimen, from the old stream-works of the Carnon Valley, in the parish of Feock, near Falmouth a locality famous, for its large nuggets weighs 15*96 grams, or 10 dwts. 6 grains ; but the mass is not exclusively gold, the metal being associated with a little vein-quartz, J It is known that gold occurs in situ in a large number of localities in Cornwall, though it is not generally recognised in tin -lodes. Many years ago Arthur Dean found it in the Great Dowgas Mine, near St. Austell, and in several lead and copper-lodes near Falmouth ; Mr. John Garby obtained it from a cross -course at Wheal Sparnon, near * On Cornish stream-tin consult Kenwood " On the Detrital Tin-ore of Cornwall,"- Journ. R. Inst. Cornwall, vol. iv., p. 191 ; and Collins, ibid., vol. xii., p. 64. t " Alluvial Deposits in the Lower Portion of the Red River Valley, near Camborne." By F. J. Stephens, F.G.S. Trans. Geol. Soc. Cornwall., vol. xii. (1900) p. 324. J Borlase states that the largest piece of Cornish gold known to him was a specimen found in 1756, weighing 15 dwts/16 grs. Greg and Lettsom cite a Cornish specimen weighing 2 ozs. 3 dwts. For British Gold, see Wall- case "No. 14. " Gold in Cornwall," Rep. Miners* Assoc. Cornwall, 1865. ASSOCIATES OF CASSITERITE. 19 Redruth ; 'and the late Mr. S. R. Pattison recorded it from David- stowe in North Cornwall.* Many other localities have been cited, and Mr. J. H. Collins remarks that few ores and gozzans are quite free from gold.f In recent years gold has been discovered by Capt. Hambly in the sands of the Menaccan River and in certain gozzans in the Gwennap district ; whilst Mr. F. J. Stephens has indicated several localities in which he has detected gold.J In Devonshire gold has been found at North Molton, especially in the gozzans of the old Poltimore copper-mine. Probably in many cases the gold has been set free on the decomposition of auriferous pyrites. An interesting group of specimens, numbered 50 to 67, is intended to illustrate the natural association of cassiterite with other minerals. This relationship, frequently so suggestive in discussing the origin of mineral deposits, is conveniently designated as paragenesis a term introduced more than half a century ago by the Saxon mineral- ogist Breithaupt. The general subject receives copious illustration in the series of veinstones arranged in the Wall-cases 27 to 30, but the small group of specimens immediately under review is limited to the associates of tinstone. The very common association of cassiterite with quartz is seen in many of the specimens, notably in Nos. 50 to 52. In No. 51 the tin-ore is attached to quartz which exhibits in places a beautiful amethystine tint. No. 54 shows the tinstone in company with quartz and apatite the latter a fluo-phosphate of calcium. Tourmaline, a very constant attendant on cassiterite, is seen with the tin-ore in No. 55 ; fluor-spar accompanies the cassiterite in No. 56 ; and topaz, in distinct crystals, may be seen alongside the tinstone in Nos. 57 to 59. The cassiterite is associated with chalybite, or carbonate of iron, in No. 52 ; with mispickel, or arsenical pyrites, in Nos. 61 and 62 ; with copper-pyrites in Nos. 63 and 64 ; with copper-pyrites and zinc- blende in No. 67 ; and with iron-pyrites and blende in No. 60. An interesting relationship is seen in No. 39, where wood-tin is seated on delicate needle-like crystals of bismuthite, or sulphide of bismuth. The study of the various associates of tin-ore will be resumed in sub- sequent pages (see especially p. 21). * " On Auriferous Quartz-rock in North Cornwall." By S. R. Pattison, F.G.S. Quart. Journ. Geol. Soc., vol. x. (1854), p. 247. -j- " On the Origin and Development of Ore-Deposits." By J. H. Collins, F.G.S. Journ. Roy. Inst. Cornwall, vol. xii. (1894), p. 49. J " The Conglomerates of Cornwall." By Captain Hambly. Rep. Corn., Polyt. Soc., 1897. " Recent Discoveries of Gold in West Cornwall." By Francis'J. Stephens F.G.S. Trans. Roy. Geol. Soc. Cornwall, vol. xii. (1898) p. 241. For other references to the gold of Cornwall and. Devon see De la Beche's Report, p. 613 ; Greg and Lettsom's Mineralogy, p. 237 ; and Collins* Minera- logy of Cornwall and Devon, p. 52. See his work, " Die Paragenesis der Mineralien." Freiberg : 1849. 7882. c 2 20 MINEBALS OF CORNWALL AND DEVON. Stannite. (No. 68.) No. 68 is a typical specimen of the mineral known as stannite or stannine, in which tin occurs to the extent of between 20 and 30 per cent, in the rare form of a sulphide. The mineral also contains copper and iron, frequently with zinc, and may be regarded as a com- plex sulphide, or probably rather as a sulpho-stannate, not without some chemical kinship to the mineral known as tetrahedrite (p. 64).* Stannite is known also as tin-pyrites, the term " pyrites " being a general name applied to many metallic sulphides. By miners the mineral is termed bell-metal ore a term suggested by the colour which it usually presents, and which may be due to an intimate admixture of copper-pyrites. The colour of the purer varieties of stannite seems to be steel-grey or iron-black rather than yellowish. This mineral was originally discovered at Wheal Rock, near St. Agnes, and has since been recorded from a great number of Cornish localities. At one time it occurred at Carn Brae, near Camborne, in sufficient quantity to be raised as an ore. Granite impregnated with tin-ore, partly in the form of stannite, has been found at Stenna Gwyn, in the parish of St. Stephens. Crystallised stannite is very rare, and the crystals even when they do occur are often indistinct, so that their type of symmetry has been open to some doubt. It has, however, been shown by Mr. L. J. Spencer that the species belongs to the tetragonal system, and presents forms closely related to those of copper-pyrites.f The Cornish stannite is usually massive, though imperfect crystals, often regarded as cubic, are not unknown. By the decomposition of stannite the metals which it contains may become converted into oxides and hydroxides, giving rise to a product which has been described under the name of cupro-cassiterite. It has been said that in some tin lodes, the metal occurs as an oxide in the shallow workings and as sulphide in the deeper parts. If this really occurs, it must be quite exceptional, the normal condition of tin-ore even in the most profound parts of a lode being that of cassiterite. The tendency of tin to combine with oxygen rather than with sulphur is seen in the alteration which ancient Roman bronzes have suffered on prolonged exposure to thermal waters. Thus, at Bourbonne-les-Bains the bronze medals showed an incrustation of oxide of tin associated with copper sulphides the two metals of the alloy exposed to like conditions having yielded quite different types of alteration-products. It is to be regretted that the term stannite is ambiguous, inasmuch as it has also been sometimes applied to a mineral substance which seems to be a mechanical mixture of cassiterite and quartz. (See No. 80, p. 23). * " Tabellarische Uebersicht der Mineral! en nach ihren krystallographisch- chemischen Eeziehungen : Geordnet von P. Groth." 4 Aufl. 1898, p. 39. t " Crystallised Stannite from Bolivia." By L. J. Spencer, M.A. With Analyses by G. T. Prior, M.A. Min. Mag., vol. xiii. (1901), p. 54. QUARTZ. 21 DIVISION 2. MINERALS OF CORNWALL AND DEVON. MINERALS ASSOCIATED WITH CASSITERITE. (Not. 69 to 136.) Numerous examples of the minerals which, occur in company with the ores of tin are here grouped together, forming a much larger collection of such minerals than is exhibited in the opposite Division of the Case, and thus giving a wider view of their paragenetic relations. All the specimens here exhibited have been obtained from Cornwall and Devon, but it has not been deemed desirable to limit the collection to specimens actually found in tin-lodes, inasmuch as these may not in all cases fully illustrate the characters of the several species. Quartz. (Nos. 69 to 80.) This is by far the most common mineral of the tin-veins, forming in some cases the sole matrix of the ore. The vein-quartz is usually white and opaque, rather fatty in lustre,and either compact or cry- stalline in texture. When granular it is known to Cornish miners as sugary spar. Microscopic cavities with liquid inclusions usually abound. It is generally supposed that the vein-stuff must have been deposited from solution. Thermal waters, from deep-seated sources, circulating through the vein fissures, might carry silica in solution and deposit it on the walls of the cavities. In those lodes which are termed comby* and exhibit a succession of plates of mineral matter, more or less parallel, it is clear that the quartz, which is usually abundant in such lodes, must have been formed in successive deposits on the walls of the veins, inasmuch as the crystals have their apices directed from the walls inwards, and in certain cases the points of the crystals in opposite layers meet and engage each other, like the teeth of two combs. Many comby lodes prove, by their structure, that the same fissure must have been re-opened, perhaps several times, and fresh vein -stuff deposited. The deposition of mineral matter in parallel bands in a vein was termed by the late Professor Posepny crustificationj since the succes- sive deposits from a series of crusts, following each other in regular sequence. Beautiful examples of banded or " ribband veinstones" as well as of " comby lodes " are exhibited in Wall-cases 29 and 30. Although the quartz in these veinstones is probably due to hydro- thermal action, it is notable that deposits from hot springs rarely * For description and figures of comby lodes see De la Beche's " Report on the Geology of Cornwall, Devon, and West Somerset " (1839) pp. 339-342. f " The Genesis of Ore-deposits." By Prof. Franz Posepny. Trans. American Inst. Mining Engineers, vol. xxiii. (1894), p. 197. Reprinted, with other papers on the subject, in a separate volume. 1902. 22 MINERALS OF CORNWALL AND DEVON. contain quartz. In siliceous sinter the silica usually exists in the hydrated opaline condition ; but crystalline quartz has occasionally been found, as in the sinter of Furnas, in the Azores, and in deposits from the warm springs of Mauhourat near Oauterets. Temperature and time are no doubt important factors in the process of crystallisa- tion. As far back as 1845 Schafhautl obtained quartz in a crystallised condition by heating precipitated silica in a Papin's digester. In Daubree's classical experiments, crystals of quartz, beautifully formed, though minute, were obtained from the decomposition of glass by means of strongly superheated water.* It has been shown, however, by M. KroustchofE that crystallised quartz may be formed at a temperature less elevated than that employed by Daubree. In KroustchofPs experiments an aqueous solution of silica was kept for several months in a closed vessel, and exposed periodically to a temperature of 250C., when crystals of quartz were obtained, of a similar type to Daubree's, and of a very notable size, some of the prismatic crystals reaching a length of 8 mm.f W. Bruhns has shown that distinct crystals of quartz may be formed by exposing either amorphous silica or powdered glass to the action of water containing ammonium fluoride at a temperature of 300C. for a period of ten hours. J Here the fluorine seems to act as a mineralising agent, or agent in determining crystallisation. Much of the quartz of the tin-lodes must have been deposited during the early phases of their history, whilst the tin-bearing fluorine com- pounds were in activity. It has been suggested that some of the quartz may represent the silica set free on the decomposition of hydrofluosilicic acid by means of water. During the alteration of the felspathic minerals of granitic rocks into kaolin an alteration not uncommon in many parts of Corn- wall free silica must be eliminated. Whether the decomposition were effected by hydrofluoric acid from below or by carbonic acid from above, the silica of the alkaline or alkaline-earthy silicate of the felspar would, in either case, be parted from its base. The nascent silica probably assumed in most cases an opaline state, but it is con- ceivable that under certain conditions it might crystallise. Certain doubly-terminated crystals embedded in china-clay, and apparently destitute of basal attachment, have been tentatively referred to such an origin. The general characters of quartz will be fully considered when dealing with the sparry minerals of the lodes displayed in Case VI. (p. 90). In the Case under present review there is exhibited only a small series of specimens, yet sufficient to illustrate the crystalline * " Etudes synthetiques." Par A. Daubree. 1879, p. 164. f " Nouvelles syntheses du Quartz et de la Tridymite." Par M. K. de Kroustchoff. Bull, de la Soc. Fran. Min., tome x. (1887), p. 31.J $ *' Beitrage zur Mineralsyn these." Neues Jahrbuch. 1880, ii., p. 62. " Traite des Gites Mineraux et Metalliferes." Par Ed. Fuchs et L. de Launay, Tome ii., 1893, p. 109. APATITE. 23 characters and the varied colours ot the Cornish quartz. The beautiful tints of the purple amethyst are well seen in Nos. 77 to 79. (For amethyst see p. 92.) In the tray, No. 80, are two specimens of the mineral substance from St. Agnes unfortunately called stannite unfortunately, because the same name has been given to the tin-copper-iron sulphide known as bell metal ore, described on p. 20. The so-called stannite,.No. 80, seems to be a mechanical mixture of quartz and cassiterite, but has sometimes been described as a silicate of tin. One specimen hero exhibited is massive, and the other crystallised. The crystals are six-sided prisms resembling those of quartz, and have been regarded as imperfect pseudomorphs. Although stannite is not truly a silicate of tin it is interesting to note that a silicate containing tin and calcium from Cornwall has been described by Dr. A. Hutchinson, of Cambridge, who has named it Stokesite after the late Sir G. G. Stokes. The unique specimen on which the species was founded occurred on axinite, from St. Just, and in its appearance was suggestive of gypsum, but crystallised in the orthorhombic system.* Apatite. (Nos. 81 to 96.) Although apatite was recognised as a distinct mineral species by the Saxon mineralogist, Werner, at least as far back as 1786, and was soon afterwards found, by the analyses of Proust and of Klaproth, to be a phosphate of lime, yet it was not until 1827 that it became recognised, through the work of Gustav Rose, that the phos- phate in this mineral was associated with either a chloride or a fluoride of calcium, or with both. Hence two varieties came to be distinguished chlor-apatite and fluor-apatite, of which the latter is the more common. The mineral which accompanies the Cornish tin ore is a fluor-apatite a fact harmonising with the part which fluorine is believed to have played as a vehicle of tin. In the south of Norway veins of apatite are very numerous, and Prof. J. H. L. Vogt has instituted an interesting comparison and contrast between these veins and those which carry tin ore.f Both occur in plutonic rocks, but the cassiterite-veins in rocks of acid type, like granite ; the apatite-veins in basic rocks, like gabbro. Whilst fluorine was active in the extraction of tin from the acid magma, chlorine appears to have been the chief agent in extracting the minerals of the apatite veins from the basic magma. Hence the Norwegian phosphate is a chlor-apatite, and that of the tin-lodes a fluor-apatite. The apatite- veins carry titanium a metal having certain chemical relations with tin ; and both metals occur in the veins as dioxides the tin as cassiterite, the titanium as rutile. The * " On Stokesite, a new mineral containing tin, from Cornwall." By A. Hutchinson, M.A. Min. Mag., vol. xii. (1900), p. 274. t " Problems in the Geology of Ore-deposits." Trans. Amer. Inst. Min. Eng., vol. xxxi. (1902), p. 125. 24 MINERALS OF CORNWALL AND DEVON. pneumatolytic action concerned in the formation of the tin- veins has metamorphosed the neighbouring granite into greisen an acid felspar being partly converted into topaz, which is a mineral contain- ing fluorine ; whilst similar action in the case of the apatite -veins has converted a basic felspar into scapolite, a mineral containing chlorine. Dr. Vogt has estimated that in the tin-lodes there is at least 100 times, and perhaps 1,000 times, as much fluorine as chlorine, while in the apatite veins these proportions are reversed. Although apatite is a characteristic associate of tin-ore in Corn- wall, it is by no means common in well-defined crystals. Its direct association with cassiterite may be seen in No. 81, and again in No. 54. It is a mineral widely distributed through igneous rocks, especially those of basic type, but usually in only microscopic crystals. Apatite is characterised by much stability, and must have crystallised out of the magma at a high temperature. That it belongs to the first phase of consolidation is evident from its common occurrence as inclusions in all other essential minerals, even in magnetite, which itself is generally one of the earliest to separate. The specimen No. 88 shows the apatite in association with axinite, from the " greenstone " cliffs near Botallack. In No. 83 the apatite occurs in short six-sided prisms, of beautiful blue colour, associated with lithia mica, from St. Michael's Mount. The granite at this famous locality is traversed by miniature tin-lodes, the walls of some of the joints being studde3myth, F.R.S., at the Annual Excursion of the Mining Association and Institute of Cornwall." Proceedings of the Assoc., vol, i., part 3, 1887. t " On Francolite, a supposed New Mineral." By T. H. Henry, Esq., F.R.S. PUL Mag., vol. xxxvi. (1850), p. 134. J Journ. Chem. Soc., [2] vol. ix. (1871). p. 3. TOPAZ. 25 nature.* All the examples of francolite shown here were obtained by the late Mr. Tailing from Fowey Consols, near Lostwithiel. It will be seen that in some of these specimens the mineral occurs in the form of small white hexagonal plates, with curved faces. Franco- lite from deep workings at Levant Mine, St. Just, has been described by Mr. R. H. Solly.f Topaz. (Nos. 97 to 99.) Topaz occurs in certain granitic rocks, perhaps in some cases as an original constituent, and is not uncommon in the rocks of the West of England. Dr. Teall has described its occurrence in a variety of granite from Meldon, near Okehampton, in Devonshire.} In most cases topaz is a secondary mineral, resulting usually from the alteration of felspar. It is a characteristic constituent of the greisen, or altered granite which occurs in the neighbourhood of certain tin- lodes. In the process of kaolinisation, part of the silica and all the alkaline base are removed from orthoclase ; and a somewhat similar change, with addition of fluorine, might produce an aluminium fluo- silicate like topaz. In this mineral fluorine exists to the extent of 17 or 18 per cent. Prof. Penfield has shown that the fluorine may be partially replaced by hydroxyl. Such a medium as hydro- fluoric acid would probably be competent, under certain conditions, to effect the conversion of felspar into topaz. In the well-known synthetical experiments by Daubree, a substance analogous to topaz was formed by the action of fluoride of silicon on alumina at a white heat. 1 1 Topaz has been artificially prepared by MM. Friedel and Sarasin by the action of hydrofluo-silicic acid on silica and alumina, with water, at a temperature of 500C. Whilst topaz is in many cases a mineral of secondary origin, it tends itself to suffer alteration, and to pass into kaolin and micaceous minerals like sericite. The specimens of topaz here exhibited represent its occurrence at Cligga Head, (Nos. 97 and 98) and at St. Michael's Mount (No. 99). Other specimens from the latter locality will be found in the opposite division of the case (Nos. 57 to 59). The occurrence at Cligga Head, between St. Agnes and Perranporth on the north coast of Cornwall, has been studied by Mr. J. B. Scrivenor, whose paper on this subject has already been referred to.1" The topaz occurs on the face of the joints in the altered granite. The * " Note on Francolite." By F. H. Butler, M.A., A.R.S.M. Min. Mag., vol. vii. (1887), p. 164. t Min. Mag., vol. vii. (1887), p. 57. j " British Petrography." By J. J. Harris Teall, M.A. 1888, p. 316. "On the Chemical Composition and related physical properties of Topaz." By S. L. Penfield and J. C. Minor, jr. Am. Journ. Sc., vol. xlvii. (1894), p. 387. || " Etudes Synthetiques de Geologic experimentale." Par A. Daubree, 1879, p. 57. If Quart. Journ. Oeol. Soc. t vol. lix. (1903), p. 142. MINERALS OF CORNWALL AND DEVON. occurrence at St. Michael's Mount is similar. The crystals are colour- less or of pale blue tint, and some of the specimens, where not dis- tinctly crystallised, might be mistaken on a cursory inspection for quartz. Topaz, however, crystallises in the orthorhombic system, and the crystals usually present, as seen here, a prismatic habit, the prisms being striated longitudinally and presenting a perfect basal cleavage. In connection with the West of England topaz it may be men- tioned that the mineral occurs also in the granite of Lundy Island.* Fluorite. (Nos. 100 to 104.) Whilst fluorite, or fluor-spar, is the most widely distributed of all minerals which contain fluorine, it is not so common in the tin mines of Cornwall as might have been anticipated. Many tin -lodes, especi- ally in the West of Cornwall, seem destitute of fluor-spar, whilst many veins rich in fluor-spar carry no tin. Most of the crystallised speci- mens, such as the fine series exhibited in Case V., have been obtained from the copper-veins and lead -veins of Cornwall and Devon. The full description of the mineral will, therefore, be deferred until that Case comes under review (see p. 85). The specimen No. 100 shows the fluor-spar in direct association with cassiterite. The spar is known to Cornish miners as Cann. In the " china stone," or altered granitic rock worked in the neigh- bourhood of St. Austell, the walls of the joints are sometimes lined with deep purple fluorite. The mineral seems to be connected with the tin-carrying fluoric compounds, which were probably responsible for much of the alteration. Dr. Boase recorded fluor-spar from the Hensbarrow granite. Fluorite rarely occurs as a rock constituent, but it was found by the late Mr. R. N. Worth in a granitic rock on the north-western flank of Trowlesworthy Tor, on the skirts of Dart- moor, whence he called the rock Trowlesworthite.^ This is an aggregate of bright red orthoclase, deep violet fluorite, black acicular tourmaline, and a very little quartz. Prof. Bonney, who examined the rock microscopically, believes that trowlesworthite has been formed from the normal granite of the district by the replacement of quartz by fluor-spar. J Fludlite. (Nos. 105 to 109.) Several specimens of this extremely rare mineral are here exhibited. It was first detected eighty years ago by Levy, and examined by Wollaston, who found that it contained fluorine and aluminium. * " On the Occurrence of Topazes in Lundy Island." Letter by Mr. S. G. Perceval in Ged. Mag., vol. vii. (1870), p. 192. f Trans. Roy. Geolog. Soc., Cornwall, vol. x. (1887), p. 177. j Ibid., p. 180 ; also, Min. Mag., vol. vi. (1884), p. 48. " On a new Mineral Substance." Ann. Phil, [n.s.] vol. viii. (1824), p. *241. MICAS. 27 An analysis made by Dr. Brandl, at Prof. Groth's request, has con- firmed this determination, and proved that the mineral is a hydrated fluoride of aluminium.* Stenna Gwynn, near St, Austell, is the only known locality. Here it occurs in very small crystals, of pyramidal habit, belonging to the orthorhombic system. These are seated on a quartzpse matrix, and associated with cassiterite, fluorite, uranite, muscovite, and wavellite. Fluellite therefore takes its place in company with the other fluorine-bearing associates of tin-stone. Lithia Mica. (No. 110.) Lithium-bearing micas are rather characteristic of granites which carry tin -stone and tourmaline. The typical mica, called from its occurrence in scaly aggregates Lepidolite, usually presents a lilac or rose-colour, with a rather pearly lustre on the cleavage planes. The presence of a little manganese seems to be responsible for these tints. The amount of lithium may reach 5 per cent, and of fluorine 8 per cent. Boron is also usually present, as in several other minerals friendly to tin-stone. A lithium-iron mica, occurring characteristically in the stanniferous rocks of Zinnwald, in Bohemia, is known as zinnwaldite, and some of the Cornish micas in silvery hexagonal plates may be referable to this type. The Zinnwald mica has been found to contain rubidium, coesium and thallium. The presence of tin has also been recorded in certain lithia-micas, and in some cases it appears to be present in the form of microscopic inclusions of cassiterite. Gilbertite. (Nos. Ill, 112.) A yellowish or greenish micaceous mineral, observed originally at Stenna Gwynn and since found in several china- stone districts in Cornwall, as at St. Austell and Breage, has been distinguished by the name of Gilbertite a name given by Dr. Thomas Thomson, in compliment to Da vies Gilbert, the " Cornish philosopher," who was, at one time President of the Royal Society (b. 1767, d. 1839.) The specimens here exhibited show the mineral in stellate aggregates of pearly scales. Being rather unctuous to the touch, it has some- times been mistaken for talc. Gilbertite appears to be an alteration-product of felspar, and pseudomorphs of gilbertite in the form of orthoclase are known. It is probable, as Mr. F. H. Butler remarked, that in some cases the gilbertite represents one of the stages in the gradual kaolinisation of orthoclase. f The specimen No. 112 shows an association of gilbertite with crystals of apatite. ^ * " Beitrage zur Kenntniss der natiirlichen Fluorverbindungen." Vorx P. Groth. Zeitsch. f. Krystattographie, vol. vii. (1883), p. 482. f Min. Mag., vol. vii., p. 79. 28 MINERALS OF CORNWALL AND DEVON. Tourmaline. (Nos. 113 to 120.) Tourmaline is perhaps, with, the exception of quartz, the most con- stant associate of tin-ore. Doubt has, however, been sometimes expressed as to such a relationship.* It is true that crystals of tourmaline are not commonly to be seen in the lodes, but the mineral is nevertheless present in microscopic crystals distributed through the rocks of most tin-districts. Rocks which are stanniferous, whether granite or killas, are almost invariably tourmaliniferous. The tin capds, which are bands of altered rock, adjacent to the veins, and generally found near the junction of the granite and the killas, are always rich in tourmaline. The mineral is chiefly developed near the margin of intrusive masses of granite, and in the zone of contact-metamorphism. It appears to have been formed by the action of vapours containing boron and fluorine, attacking the felspathic and micaceous constituents of the rocks. Tourmaline is a boro-silicate of complex and variable constitution, containing aluminium, iron, magnesium and the alkali-metals, with fluorine and hydroxyl. The proportion of boric oxide generally ranges between 8 and 10 per cent., but may rise higher. Free boric acid is not uncommon in the exhalations from fumaroles, notably in those of Tuscany. Mr. Donald MacAlister has suggested that the metaborate of sodium, formed by the action of boric acid on the felspars, might have been an active chemical agent in the transport of tin.f According to a striking calculation by Mr. J. H. Collins, the tourma- line-bearing rocks of the West of England contain something like 2,480,000 tons of fluorine for each yard in depth, t This result is based, however, on the liberal estimate that the tourmaline contains an average of 2 per cent, of fluorine, and that the mineral constitutes 10 per cent, of the rock. Most of the tourmaline of Cornwall and Devon, though coloured in thin sections, appears black when viewed in mass by reflected light. This black, ferriferous tourmaline is known as schorl.^ It frequently occurs in acicular crystals or in fibrous masses (No. 119). In No. 118 the slender crystals are grouped in stellate aggregates. Tourmaline belongs to the hexagonal system, and commonly assumes the form of three -sided prisms, striated longitudinally, giving on transverse section characteristic triangular figures, and carrying * " La Tourmaline, loin d'accompagner re'gulierement 1'oxyde d'etain, semble exercer sur lui une action repulsive." " Note sur la Constitution des gites stanniferes de la Villeder (Morbihan)." Par M. Lodin. Bull. Gtolog. Soc. Fr. [3 serie], t. xii. (1884), p. 645. M. Lodin holds that the views of Daubree are not applicable to the tin-deposits described in this memoir. t " Tin and Tourmaline."- By Donald A. MacAlister, Esq. Quart. Journ. Geol. Soc., vol. lix. (1903), p. 53. J " On the Origin and Development of Ore-deposits in the West of Eng- land." By J. H. Collins, Cap. Ill, Journ. Roy. Inst., Cornwall, vol. xi. (1893), p. 371. The word schorl is said to be derived from the old German miners, and tourmaline from the Sinhalese. TOURMALINE. 29 rhomb ohedral faces at their extremities. The mineral is remarkable for its hemimorphism, * for its pyroelectric properties and for its optical characters. A fine series of specimens, mostly from foreign localities, and including many gem stones, will be found in the Horse- shoe Case, Section R. Magnificent crystals of black tourmaline were obtained many years ago from a small quarry of red granite not far from Bovey Tracey in Devonshire. f Examples of these bold crystals are here exhibited as Nos. 113 to 116. They were embedded in a matrix of ochreous clay in a cavity of the granite, and were associated, as will be seen in these specimens, with crystals of quartz and apatite. The crystals of tourmaline are mostly short stout prisms, with rhombohedral ter- minations ; and it is notable that whilst some of the faces are smooth and brilliant others are rough and dull. In No. 115, and in some of the other specimens, the apatite appears to have been formed after the tourmaline. The beautiful rock described by Professor Bonney under the name of Luxullianite is rich in tourmaline. { This rock consists of pink orthoclase, in large twin crystals, embedded in a dark matrix of schorl and quartz. Boulders of the rock are found at Luxullian, near Lostwithiel, and the largest known mass was used for the sarcophagus of the Duke of Wellington in St. Paul's. Specimens may be seen in the Rock Collection, and some beautiful polished examples will be found among the ornamental stones in the Hall. In many of the Cornish granites, tourmaline displaces, to a greater or less extent, the micaceous and felspathic constituents, having probably been formed at their expense, and when the replacement is complete the resulting aggregate of quartz and tourmaline is known as schorl-rock. Such a rock is associated, in several localities, with the occurrence of tin- stone. Spheroidal masses of schorl-rock may occur as enclosures in the normal granite. Whilst tourmaline may be formed by the alteration of micaceous minerals, there are circumstances under which it seems to be itself changed to mica. Topaz may likewise be an alteration-product of tourmaline. As a rule, however, the mineral is characterised by much stability, and when set free by the disintegration of a rock it may survive in the form of rolled fragments and be ground down as sand. Mr. A. Dick found that about one-tenth per cent, of the Lower Bagshot sands of Hampstead Heath, north of London, con- sisted of grains and crystals of tourmaline. * Crystals are said to be hemimorphic when their opposite extremities are dissimilarly developed, or, technically, when they possess axes of symmetry which are polar. Hemimorphism is often correlated with pyro-electric properties. t " On the Mineral Localities of Devonshire." By Townshend M. Hall. Trans. Devon. Assoc., vol. ii. (1868), p. 332. J Min. Mag., vol. i. (1877), p. 215. Nature, vol. xxxvi. (1887), p. 91. 30 MINERALS OF CORNWALL AND DEVON. Axinite. (Nos. 121 to 124.) Axirdte is a boro-silicate of complex composition, rather like tourmaline, and originally regarded as a kind of schorl. It differs, however, from tourmaline in occurring usually in basic eruptive rocks rather than in those of acid type, though not altogether un- known in the latter. If the Cornish specimens are not comparable for beauty with the fine crystals of axinite from Dauphiny they yet illustrate sufficiently the general characters of the species. They occur as clove- brown brilliant crystals, belonging to the anorthic system, with the sharp axe -like edges that suggested to Haiiy the specific name. The Dauphiny crystals, of which specimens may be seen in the Horse-shoe Case (Section 9) occur in a zone of amphibolite and chlorite schists.* Those of Cornwall are typically developed in the greenstones and hornblende schists displayed in the cliffs north of Botallack Head, at Wheal Cock and at Trewellard, north of St. Just. Some of the specimens here shown are from Terrace Hill, Lost- withiel. Pseudomorphs of chlorite after axinite are recorded from Dartmoor and from St. Just. The Cornish axinite has been analysed by Mr. J. E. Whitfield.f Wolframite. (Nos. 125 to 130.) Wolfram, or Wolframite, is a mineral which in Cornwall, as in so many other parts of the world, follows close in the train of the tin-ore. In some of the Cornish tin-lodes it has been found " inconveniently plentiful," inasmuch as it is not easy to separate it from the tin stuff by mechanical dressing, the specific gravity of the wolfram standing very near to that of cassiterite (about 7). Magnetic separation has recently been used. Wolfram occurs usually in opaque brownish -black cleavable masses, with a lustre so brilliant as to be almost adamantine. Occasionally it occurs in crystals, as seen in these specimens, which show the crystallised wolfram associated with quartz. Formerly the crystals, were regarded as orthorhombic, but they are now claimed by the monoclinic system. Wolfram is an iron and manganese tungstate, containing when pure about 60 per cent, of the metal tungsten or wolframium. It is used in the preparation of tungsten- steel, a small proportion of tungsten being found to increase the hardness and tenacity of the metal. Wolfram is raised to a limited extent from several mines in Corn- wall Cam Brea, Tin Croft, East Pool and Agar United Mines. The quantity raised in the year 1901 was, according to official statistics, 21 tons, valued at 408. * " Mineralogie de la France et de ses Colonies." By A. Lacroix, vol. i., p. 277. Paris, 1893. t Amer. Journ. Sc. [3], xxxiv. (1887), p. 286. SCHEELITE I MISPICKEL. 31 By exposure to influences which, remove the iron and manganese, wolfram becomes encrusted with a yellowish earthy coating of Wolframine or wolfram ochre, known also as tungstite. This mineral, consisting of tungsten trioxide, is seen on specimen No. 132, from East Pool Mine. Scheelite. (No. 131.) Scheelite is a calcium tungstate not common in Cornwall, but occasionally occurring as an alteration-product of wolfram. The two isolated crystals of this species shown here are little bipyramids, which, notwithstanding their resemblance to regular octahedra, belong to the tetragonal system. The other specimen in the tray, No. 131, is an example of scheelite, in a chloritic matrix, from Wheal Friendship, near Tavistock in Devonshire. The species will be again referred to in connection with the much finer specimens which occur in Cumberland (p. 153). Mispickel. (Nos. 133 to 13(5.) The solfatanc emanations which appear, from so many lines of evidence, to have arisen from an acid magma and to have been active in the formation of the deposits of tin ore in the West of England, must have been laden not only with fluorine and boron but likewise with sulphur and arsenic. The latter elements combined with iron constitute the mineral called Mispickel one of the most constant associates of tinstone.* In Case V there is a series of metallic sulphides, headed by the commonest species known as iron-pyrites. The name pyrites has come to be used as the designation of a group of related minerals, all sulphides with a metallic aspect, and in this group mispickel is included. It is, therefore, known, from its composition, as arsenical pyrites, or, since pyrites is called by Cornish miners " mundic," the mispickel is known also as arsenical mundic. The term " mispickel" itself comes from an old German name for this, or a similar mineral. Mispickel is an arseno-sulphide of iron, generally showing, when freshly fractured, a white colour and metallic lustre. It crystallises in the orthorhombic system, frequently in twin crystals. Further description of the species will be found in connection with the section dealing with pyrites (p. 62). * A solfatara ought literally to exhale vapours containing sulphur (Italian solfo). Vapour-vents emitting, at a higher temperature, chlorine compounds are often termed fumaroles ; but the nomenclature is lax. Pneumatolytic emanations were evolved from the deep-seated magma, under pressure. Probably the fluorine -bearing vapours concerned in the production of tin- ore came from the hottest subterranean fumaroles ; and it has been supposed that the sulphur-carrying vapours represented a rather cooler phase of emission. On the genesis of ore-deposits see Prof. J. F. Kemp's paper on " The Role of the Igneous Rocks in the Formation of Veins.'' Trans. Am. Inst. Min. Eng., vol. xxxi. (1902), p. 169. 32 MINERALS OF CORNWALL AND DEVON. Although mispickel occurs in both tin-lodes and copper -lodes in the West of England, it seems to be more common in the former. It is generally found in veins running through killas near to granite, but is not common in the granite itself. In some Cornish mines it seeins to have great vertical persistence, increasing in quantity down- wards, and thus leading to the inference that it may be a vein mineral of very early formation. Arsenical pyrites is still raised in Cornwall and Devon, though to a less extent than formerly. During the year 1901 the quantity of the mineral raised in Cornwall was 2,334 tons, and in Devonshire 244 tons. This arsenic ore is roasted for the production of arsenious anhydride, or " white arsenic." According to the official statistics, the amount of arsenic, partly as " soot " and partly as " white arsenic," refined at the mines, and obtained principally from the arsenical pyrites of the tin and copper mines, was 1,258 tons in Corn- wall and 2,103 tons in Devonshire. COPPER-ORES. 33 CASE II. DIVISION 1. MINERALS OF CORNWALL AND DEVON. COPPER SULPHIDES AND SULPHO-FERRITES. (Nos. 137 to 204.) The ores of copper, next to those of tin, are the most important metal- bearing minerals yielded by the mines of the Damnonian Peninsula. In the early days of Cornish tin mining the copper-ores, which were not infrequently found in association with those of tin, were altogether neglected. Carew, writing in the beginning of the seventeenth century, says : " Copper is found in sundry places, but with what gain to the searchers I have not been curious to enquire nor they hasty to reveal."* After Carew's time a hundred years had to pass before the copper-ores of Cornwall came to be systematically worked. At one time it was believed that the ores of copper in Cornwall were restricted to the western part of the peninsula a belief which found expression in the saying " No copper east of Truro Bridge." That idea was dispelled, however, long ago ; and mines of great value have been worked far beyond the old restricted limit. Never- theless, the most important workings for copper at the present time are in the extreme west. During the year 1902 Levant Mine in St. Just turned out not less than 3,056 tons of dressed copper ore. No sharp line of separation can be drawn between the deposits of copper-ore and those of tin. The lodes run in the same general direction, and in many cases the same vein may carry both tin and copper. The specimen, No. 137, shows the association of copper pyrites with crystals of cassiterite. Some mines have been worked at one time for tin, at another for copper ; and it has not infrequently happened that copper-lodes have carried more or less tinstone in their upper or gozzany part. Certain mines which were worked originally for tin ore have yielded copper ore at lower levels, and then at yet greater depths the copper has given way to tin. It has been said that in many cases the copper minerals seem to have been of later introduction than the tin ore, but it is doubtful whether such a conclusion admits of wide application. Mr. J. B. Hill believes that the copper and tin are of " approximately identical age,"f * Survey of Cornwall. Ed. 1811., p. 21. t Trans. R. Geol. Soc. Corn., vol. xii., part vii. (1902), p. 593. 7882, 34 MINERALS OF CORNWALL AND DEVON. whilst Mr. D. MacAlister thinks, with, reference to the Camborne district, that " probably the copper arrived either before the tin, or at the same time."* It has been observed that in mixed deposits the copper generally occurs where the vein traverses killas, whilst in granite it may be dis- placed by tin. Some of the lodes, for instance, near Tavistock, in Devonshire, produced copper while in killas, but only tin after pass- ing into the Dartmoor granite. At the junction of the two rocks, rich bunches of copper-ore have sometimes been found, and they have also occurred in the killas far from any visible granite. The primary condition of the copper in the veins of Cornwall and Devon, as in many other copper-mining localities, appears to be that of copper-pyrites a sulphide of copper and iron, containing theoretic- ally about 34 per cent, of metallic copper. In the higher part of the vein the pyrites may be associated with, or even replaced by, the richer copper sulphides known as purple ore and copper glance. The sulphides thus become progressively richer in copper as the} approach the surface an enrichment probably due, at least in part, to the removal of the iron sulphide in the copper-pyrites, by means of solution. The succession of minerals may be represented in descend- ing sequence as follows, though the order may be subject to much local irregularity. Copper glance (Chcdcorite), with 80 per cent, of copper. Purple copper ore (Erubescite), ,,55 . Copper pyrites (Chalcopyrite), ,,34 ,, It is worth noting that at the famous copper mines of Monte Catini, in Tuscany, there are nodules of ore which show a succession of minerals arranged in zones following the same order. The central part of the nodule is copper pyrites, which passes into purple ore, and this gives way towards the exterior to copper glance, whilst even native copper may appear on the surface. It seems fair, however, to point out that successive changes of precisely the inverse order may be traced on metallic copper after prolonged exposure to the action of thermal waters. Roman bronze coins, for example, found in the spring of Bourbon-l'Archambault, in Central France, have exhibited a central core of unaltered metal, followed from within outwards by successive zones of copper glance, purple ore and copper pyrites.f Mr. S. F. Emmons has observed that as the tendency to establish a condition of chemical equilibrium in a reaction may be modified by varying conditions of temperature, pressure and strength of the reacting solutions, it is conceivable that the reaction may proceed in the reverse direction under altered con- ditions. The concentration of copper in the region of rich sulphides may be due, not only to the removal of the iron from copper-iron sulphides, but also to the direct deposition of copper sulphide from circulating * Trans. E. GeoL Soc., Corn., vol. xii., part viii. (1903), p. 773. f Comptes Rendus, vol. Ixxx. (1875), p. 1297. CHALCOPYRITE. 35 solutions. This secondary enrichment has been ably discussed by such geologists as Prof. S. F. Emmons* and Mr. W. H. Weed.f Near the surface copper-pyrites would be prone to oxidation, and the copper sulphate so formed and carried downwards in solution might suffer reduction not only by organic matter but by such metallic sulphides as iron pyrites, and thus a precipitate of fresh sulphide of copper might be produced. In the copper- veins of Cornwall, as pointed out by the late Mr. Arthur Collins, three zones may be roughly recognised, though in many cases they are by no means sharply separated : 1. Zone of oxidation or weathering, which will be described under the head of gozzans (p. 41). 2. Zone of sulphide enrichment, in which the secondary sulphur- etted ores have been produced. 3. Zone of primary sulphide, which may be copper-pyrites, or poor cupriferous iron pyrites. In the West of England the rich ore-belts have in many cases been passed through, and a region of impoverished ore has been reached. " Copper mining," wrote Sir C. Le Neve Foster^ " is an industry which is rapidly decreasing in importance in Britain." During the year 1902, the mines of Cornwall produced 4,547 tons of dressed copper ore, valued at 12,374 ; whilst in Devonshire only 350 tons were raised, having a value of 637. Chalcopyrite. (Nos. 137 to 164.) The most^common ore of copper in the mines of the West of Eng- land, as in so many other localities, is a combination of copper, iron and sulphur, constituting the mineral usually known as Copper- pyrites. By mineralogists it is now generally designated by Beudant's name Chalcopyrite. A suggestion made long ago by Brooke and Miller that the mineral should be termed Towanite, after Wheal Towan, a mine near St. Agnes, which yielded fine crystals of this species, is a suggestion which was never widely adopted. By miners the mineral is generally known as yellow ore. When the tinstone of a lode is replaced by a deposit of this ore, the miner would say that " The yellows cut out the tin." Chalcopyrite crystallises in the tetragonal system, usually in hemihedral forms. The crystals present a sphenoidal habit, with the faces in many cases curved and striated. Twin crystals are * " The Secondary Enrichment of Ore -deposits." Trans. Am. Inst. Mining Eng., vol. xxx. (1901), p. 177. f " The Enrichment of Gold and Silver Veins." By Walter Harvey Weed, Ibid., p. 424. J Home Office Report (part III., Output). 1903, p 200. A Hemihedral form is one in which only half the number of faces required by the full symmetry of its system are developed. It may be re- garded as formed from a holohedral form by the synynetrical suppression of half the faces. 7882. D 2 36 MINERALS OF CORNWALL AND DEVON. common. The angles of the sphenoid are so close to those of the regular tetrahedron that the species was referred to the cubic system until the measurements of William Phillips, aided by Levy, in 1822, showed that " pyritous copper " was not cubic.* At the same time the mineral was carefully analysed by his brother Richard Phillips. Crystals of Cornish chalcopyrite have been studied by Mr. L. Fletcherf and by Professor J. W. LewisJ, not to mention continental crystallographers. For good crystals, see Nos. 138 to 153. Although crystals of chalcopyrite are common enough in collec- tions, the mineral usually occurs in the Cornish lodes in compact or amorphous masses. In some cases it presents mammillary and botryoidal forms, which are known as Blister ore. Such forms are seen in Nos. 161 to 164. Chalcopyrite presents a rich golden yellow colour, but tends to tarnish on exposure. The tarnish is sometimes brilliantly iridescent, when the mineral becomes known as peacock ore (Nos. 154, 155). Iron-pyrites may be associated with copper-pyrites as an intimate mechanical mixture, and in this way the latter loses its character- istic colour, becoming much paler. The two kinds of pyrites are distinguished not only by colour but by hardness, the copper-pyrites yielding readily to a knife whilst the iron-pyrites is too hard to be scratched by a steel point. In chalcopyrite the three constituent elements are present in nearly equal proportions. The formula for chalcopyrite, CuFeS 2 , yields : copper 34*6 per cent., iron 30'5, and sulphur 34" 9 ; but analyses often show an excess of iron, probably due to admixture with iron-pyrites. It is usual to regard chalcopyrite as a double sulphide of copper and iron, and since it yields, by alteration, copper glance (Cu 2 S) it is supposed to contain a molecule of cuprous sulphide, whence its formula is often written Cu^Fe^S^ . But chalcopyrite may also be viewed as a sulpho-ferrite ; that is to say, it may be regarded as a derivative from a sulpho-acid, FeS 2 H, by replacement of the hydrogen by univalent copper. The recent formation of copper^pyrites has been illustrated by the action of thermal waters on objects containing copper. Thus, at Bourbonne-les-Bains and at Bourbon-l'Archambault, in Central France, copper-pyrites has been formed on old Roman bronze coins. The sulphur in such cases is supplied by the sulphates which the * " On the Crystalline Form of Yellow Copper Ore." By William Phillips. Annals Phil, [n.s.], vol. iii., p. 296. f " Crystallographic Notes." By L. Fletcher, M.A. Proc. Crystal- lological Soc., part ii. (1882), p. 114. Also Groth's Zettsch. Kryst., Bd. vii. (1883), p. 321. J " On some remarkable Composite Crystals of Copper Pyrites from Cornwall." By Prof. W. J. Lewis, M.A., and A. L. Hall, B.A. Min. Mag., - vol. xii. (1890), p. 324. " Tabellarioche Uebersicht der Mineralien nach ihren krystallographisch- chemischen Beziehungen. Geordnet von P. Groth." 4 Auf., 1898, p. 29. CHALCOCITE. 37 waters contain, and which are reduced to sulphides by the decom- position of organic matter. Crystals of copper-pyrites have also been formed inside the copper tubes used for conveying thermal waters near Pest.* The paragenetic relations of copper -pyrites are well illustrated by the specimens in the Case under review. No. 137 shows chalco- pyrite and cassiterite side by side. The common association with quartz is seen in many of the specimens, notably in Nos. 139, 140, 149, 150, and 153. With calcite the Cornish chalcopyrite occurs much less frequently, but examples are shown from the Caradon mines in No. 147. Chalybite, or carbonate of iron, is a frequent com- panion of copper-pyrites, as seen in Nos. 142 and 145. In No. 158 chalcopyrite is associated with, fluor-spar ; in Nos. 140, 156, and 157, with fluor-spar and quartz ; and in No. 160 with francolite, a variety of apatite. Copper-pyrites also occurs, rather exceptionally, with boro-silicates like tourmaline and axinite, as at the Belstone mines, in Devonshire, whence was obtained the specimen No. 159, which exhibits the interesting association of chalcopyrite with garnet and axinite. f Chalcocite. (Nos. 165 to 192.) Next to chalcopyrite, copper glance is the most abundant ore of copper. This is a native cuprous sulphide, known to mineralogists under a variety of names, such as Chalcocite, Redruthite, and vitreous copper ore. It occurs usually in the upper part of the lodes, above the copper-pyrites, though in some cases the two sulphides are inter- mingled. Probably much of the chalcocite may be regarded as a secondary sulphide, produced by the alteration of copper-pyrites. A large series of Cornish specimens of chalcocite, exceptional for their beauty, is exhibited in this Case. The mineral crystallises in the orthorhombic system, and some typical examples illustrating its prismatic habit are here shown (Nos. 170, 171). The name redruth- ite, sometimes applied to this species, recalls the fact that many of the finest crystals have been brought to light from mines in the neigh- bourhood of Redruth. In many cases the crystals assume a hexa- gonal habit which led some of the early mineralogists to refer the species to the hexagonal system. Many fine examples of these pseudo-hexagonal crystals, principally from St. Ives, will be recog- nised here, notably Nos. 172 to 175. Twin crystals and triplets are not infrequent, giving rise to star-shaped structures. It is easy to understand from the shape of some of the crystals how the miners have been led to call them " nail -headed copper ore." Chalcocite is usually of a dark lead-grey colour, but many of the crystals when fresh present a brilliant steel-grey appearance. On exposure, the mineral is apt to suffer alteration, and acquire a dull * " Lehrbuch der Miner alogie." Von Dr. Gustav Tschermak, 4 Auf., 1894, p. 354. f " Notes on Minerals from Cornwall and Devon." Py R. H. Solly, M.A., F.G.S. Min. Mag., vol. vi. (1886), p. 202. s 11 ^****^^ f or THE ' \ I UNIVERSITY ) 38 MINERALS OF CORNWALL AND DEVON. black surface. In other cases the surface becomes encrusted with the blue copper sulphide, called covellite. It may also become coated, under the influence of meteoric agencies, with copper carbonates and other epigenic minerals, as is illustrated by No. 189 a beautiful specimen of copper glance in which malachite is creeping over the crystals. Chalcocite is remarkably soft, sectile and fusible : so soft as to be readily cut with a knife, like a piece of horn, and so fusible as to melt in the flame of a candle. When massive as an ore it is some- times called " black copper ore " and " grey copper ; " but these names are ambiguous, inasmuch as the former is applied also to the oxide called melanconite, and the latter to fahlerz or tetrahedrite. Some forms of chalcocite are pulverulent and sooty. Copper glance usually, though not invariably, occurs near the out- crop of an ore-deposit, and gives way in depth to the yellow and purple ores. Pseudomorphs of chalcocite after chalcopyrke are known, and von Jeremeeff described their occurrence in quartz veins near GeorgeifE, in the Altai, where every stage from copper-pyrites to copper glance may be traced.* It should be noted, however, that the converse change likewise occurs, pseudomorphs being known in which copper-pyrites has replaced copper glance. Chalcocite may be produced by the reaction of sulphate of copper on copper-pyrites or even on iron-pyrites. It is known as a pseudo- morph replacing organic structures, and some specimens of wood mineralised with chalcocite are shown in the Case of specimens illustrating Fossilisation. Roman bronze coins, and other objects containing copper, after exposure to the prolonged action of certain thermal waters, have yielded crystallised chalcocite. Some of Daubree's well known examples from Bourbonne-les-Bains exhibited crystals of cuprous sulphide which strongly reminded the mineralogist of the natural crystals of Redruth, on a small scale. Covellite. (Nos. 191, 192.) Whilst cuprous sulphide constitutes the mineral described above as chalcocite or copper glance, the cupric sulphide (CuS) also occurs native and forms a mineral known as Covellite. This name was given to it as a compliment to Covelli, an Italian mineralogist who showed that cupric sulphide occurs among the erupted products of Vesuvius. It is easy to understand how such a substance may be formed, by the reaction of sulphuretted hydrogen on cupric chloride, which is a volatile body found among certain volcanic exhalations. Whilst the Vesuvian covellite is crystallised in forms belonging to the hexagonal system, the covellite in copper- veins is usually found as a blue incrustation on other copper sulphides, from which it has evidently been derived. It is not uncommon as an alteration-pro- duct on chalcocite, chalcopyrite and erubescite ; witness such * Zeit. f. Kryst., vol. xxxi. (1899), p. 508. ERUBESCITE. 39 specimens as are shown here. By Breithaupt it was called Kupfer- indig, or indigo copper, since it bears some resemblance to indigo not only in colour but in general appearance. It has been shown experimentally by A. Knop that covellite may be formed by the action of hydrochloric acid on copper glance or on purple copper-ore in the former case rapidly, in the latter slowly. Some of the copper is removed as chloride, and the cuprous sulphide (Cu S) by this loss of copper passes into the condition of cupric sulphide (CuS).* Hochstetter recorded the occurrence of covellite as a thick dark blue incrustation on an axe-head of bronze and on metallic copper from a prehistoric site near Hallstatt, in Austria.f Erubescite. (Nos. 193 to 204.) Cornwall is remarkable, among mineral localities, for its fine crystals of chalcocite already described, and not less for its crystals of Erubescite. These crystals have been obtained chiefly from the mines of Cam Brea, Tincroft, and Cook's Kitchen three typical localities near Redruth. Erubescite crystallises in the cubic system, and many of the specimens here exhibited show characteristic forms, such as inter- penetrating cubes. It will be noted that some of the faces are slightly curved, and in many cases the crystals instead of being distinctly developed are confusedly aggregated, whilst in some cases the groups of crystals take a marked linear extension. When freshly fractured the mineral presents a bronzy or coppery appearance, but it rapidly suffers tarnish, especially in moist air, and frequently becomes iridescent. The name erubescite, given by Dana, is suggestive of the reddish tint which the mineral sometimes assumes. In most cases, however, the superficial colour tends towards purple, probably due to the formation of covellite, whence the common name purple copper-ore. The tarnished surface is often vivid in lustre and varied in tint so varied that the German miners call it Buntkupjererz, or variegated copper-ore. In consequence of the bluish red appearance of the mineral, the Cornish miner com- monly terms it horse flesh ore. Erubescite was regarded by the early mineralogists as a form of copper-pyrites, and it was not definitely separated from this species until its crystalline characters and chemical composition came to be understood. William Phillips first showed that the mineral was cubic, and in his honour Beudant named it Phillipsite, a name which is unfortunately ambiguous, since it is applied also to a certain zeolitic mineral. Among the many designations of this copper-ore is included the name Bornite, applied to it in compliment to Ignatius von Born, a mineralogist who had charge of the mineral collection in Vienna in the latter part of the eighteenth century. This name, * Neues Jahrluch, 1861, p. 533. f Sitzungsber. Ak. Wiss. Wien. Bd. Ixxix., Abth. I. (1879), p. 122. 40 MINERALS OF CORNWALL AND DEVON. given as far back as 1845, seems in truth to have priority over Dana's erube.cite, but the word bornite is apt to be confused by rr.iners with bournonite. Purple copper-ore is generally regarded as a double sulphide of copper and iron, chemically akin to yellow copper-ore. Pure speci- mens conform to the formula Cu 3 Fe S 3 , but the massive ore exhibits considerable variation in composition, probably due to mechanical mixture with copper glance or with copper-pyrites. According to Rammelsberg, erubescite maybe viewed as a combination, in varying proportions, of the three sulphides Cu 2 S and Cu S and Fe S. Groth's view regards it as a sulpho-ferrite of copper, derived from the normal sulpho-acid Fe (SH) 3 by replacement of its hydrogen by copper : Fe (S Cu) 3 . The specimen No. 204 is notable for showing the erubescite in the form of lenticular chalcocite, and in association with calcite. The psaudomorphs after chalcocite suggest one way in which it may have been formed. It is probable, however, that in many cases it has resulted from the alteration of copper-pyrites, and perhaps even of iron-pyrites, by the action of waters containing copper sulphate. Illustrations of the neogenic formation of erubescite are furnished by the Roman coins and other bronze objects, which were thrown as votive offerings into certain thermal springs, as at the famous waters of Bourbonne-les-Bains, described long ago by Daubree. After exposure to the action of these waters for some sixteen centuries, the metal objects have become partially converted into various copper-bearing sulphides, such as chalcocite, chalcopyrite and erubescite. The subject will be referred to again, in connection with the mineral called tetrahedrite, which has also been formed, and is perhaps the most interesting of all these epigenic formations. DIVISION 2. MINERALS OF CORNWALL AND DEVON. COPPER-BEARING MINERALS OF THE GOZZANS. (Nos. 205 to 272.; In a mineral- vein which carries pyrites in any form, it is usual to find that the upper part of the deposit contains much brown oxide of iron, or ferric hydrate. This rusty ore has resulted from the alteration of the pyritic constituent of the lode under the influence of oxidising agencies, and is therefore practically confined to the zone of weathering. It usually marks the " back " or outcrop of the lode. A tin-lode fairly free from pyrites is not likely to carry a ferruginous capping of great extent, but most tin -lodes contain more or less iron pyrites or mispickel, which may yield on decomposition hydrated oxide of iron. In copper-lodes, however, this ferruginous mass is GOZZANS. 41 usually present in conspicuous amount, the iron of the copper-pyrites yielding the brown hydrate ; and its characteristics are held by ex- perienced miners to bear some relation to the nature of the underlying ore-body. The oxide of iron is generally associated with much of the quartzose veinstone, which is apt to present a cavernous or honey- combed aspect, due to removal of the pyritic minerals. This cellular mass of ferruginous matter is known in Corn wall as gozzan, in France as the chapeau de fer, and in Germany as the eiserner Hut. The connection between gozzan above and ore below has been regarded as so well established that it has given rise among German miners to an old adage, which has appeared in several English variants : " A Lode that wears no iron hat, Is never likely to be fat." Since the formation of the gozzan is generally due to the alteration of pyrites, or in some cases to the alteration of carbonate of iron, it may be assumed that it will be found only in the shallow part of a mine, in the upper zone above the water level of the country, or in what the late Prof. Posepny termed the vadose region. * Below the plane of saturation, whither the influences that effect oxidation fail to penetrate, the metallic sulphides may retain their original character with but little alteration. It may happen, however, that these agencies, operating along deep fissures, make themselves felt at con- siderable depths. Thus in Cornwall the gozzan has extended to as great a depth as 100 fathoms below the adit level at Fowey Consols : in Ting Tang Mine the gozzan went down to 150 fathoms ; whilst at Dolcoath oxidised products have been found as deep as the 197 fathom level. | In the weathering of iron-pyrites the sulphide is oxidised to the condition of ferrous sulphate, with formation of free sulphuric acid. This sulphate, perhaps after passing to the condition of ferric sulphate, is ultimately converted into ferric hydrate, or, as it is sometimes called, hydrate of iron. The reactions in the oxidation and hydration of pyrites have been studied by Mr. W. H. Weed and by Mr. R. A. F. Penrose.J It is probable that the alteration of pyrites to limonite is often effected through the intermediate formation of ferrous carbonate, a rather unstable compound easily decomposed in the presence of air and water, with production of ferric hydrate. Dr. J. W. Evans has called attention to the action of carbonates in promoting the limonitisation of pyrites. His experiments showed that metallic sulphides exposed to water free from carbonates are usually con- verted into sulphates, but that the presence of carbonates determined * On the circulation of subterranean water, see Prof, van Hise's papers : " Principles controlling the Deposition of Ores." Journ. Geol., vol. viii. (1900), p. 730. Trans. Am. Inst. Min. Eng., vol. xxx. (1901), p. 27. t On Cornish Gozzan, often spelt Gossan, see W. Argall in Rep. Min. Assoc., 1872, p. 37. Also J. H. Collins in Journ. R. Inst. Corn., vol. ix., p. 471. J Journal of Geology, vol. ii. (1894), p. 288. 42 MINERALS OF CORNWALL AND DE\ON, the formation of oxides, hydrates and carbonates. In the case of iron-pyrites, the first product of alteration in the presence of carbonates is usually the hydra ted oxide.* The specimen No. 205 is a sample of gozzan from a copper-lode at Devon Great Consols. A large series of examples will be found among the vein-stones in Wall-case 35. They are not showy speci- mens, but are of much significance to the miner, since the character of the gozzan usually bears some relation to that of the ore-body, though sometimes it happens that a rich gozzan may cap a lean lode. To the mineralogist the gozzany part of a vein is often of supreme interest, for many of the finely crystallised specimens of oxides, carbonates, phosphates, arsenates and other oxysalts, have had their birthplace in the region of the gozzan. An extensive series of such specimens, including many of great beauty, is exhibited in the Case under description and in some of the succeeding Cases. Cuprite. (Nos. 206 to 226.) Two oxides of copper occur in a native condition the red or cuprous oxide (Cu 2 0) and the Hack or cupric oxide (CuO), forming the minerals known respectively as cuprite and melaconite. In the mines of Cornwall and Devon these copper oxides have usually been derived from the alteration of copper sulphides. Cuprite, or red copper ore, not unfrequently occurs in sharply defined crystals, of the cubic system, rich in colour and brilliant in lustre. The crystals, as shown here, are usually octahedra, or less commonly cubes and rhombic dodecahedra. Some of the specimens (such as Nos. 210, 214, 215) present a colour, lustre and translucency which justify the name of ruby copper ore, sometimes applied to this specif ;S. As the mineral is apt to become dull and opaque by pro- longed exposure to light the finest specimens are not exhibited in this Case. Wheal Phoenix, near Liskeard, yielded at one time crystals of cuprite, which in beauty and brilliancy rivalled gem stones ; and many of these specimens are preserved in japanned tin cases in the Ludlam cabinets, where they may be seen by students, on application to the curator. A remarkable variety of cuprite is furnished by the capillary forms known as Chalcotrichite or plush copper (Nos. 225, 226). These delicate filaments, of carmine colour and silky lustre, are acicular crystals, the system of which was formerly a matter of dispute ; but they are now known to be cubes greatly elongated, usually in the direction of a diagonal. In many of the specimens, such as Nos. 206 and 207, the associa- tion of cuprite with limonite reveals its origin from copper-pyrites, the sulphides of the two metals, copper and iron, being here repre- sented by the oxides. An intimate mixture of cuprite and limonite is sometimes found as an earthy substance, brick red or reddish brown in colour, and is known to miners as tile ore. * " The Alteration of Pyrite by Underground Water." By John W. Evans, LL.B., D.Sc. Min. Mag., vol. xii. (1900), p. 371. CUPRITE AND MELACONITE. 43 At the beginning of the nineteenth century, great discoveries of red copper- ore were made in Cornwall, where it had previously been a very rare mineral. Mr. W. Phillips described and figured the fine crystals from Wheal Gorland, near St. Day in Gwennap.* Here there were three lodes, but most of the cuprite was yielded by the gozzany part of the Muttrell Lode, " one to which no other lode hitherto discovered in the county of Cornwall bears any analogy." The gozzan extended to a considerable depth, and yielded a great deposit of cuprite, associated with native copper, copper glance, black oxide and arsenate of copper, mispickel, quartz and fluorspar. It is believed that many of the specimens of cuprite here exhibited were obtained from this deposit. Cuprite is not unfrequently found in a crystalline condition on ancient objects of copper or bronze, which have lain long in damp ground. Bronze celts sometimes show this alteration. The surface of the object is coated with green carbonate of copper, beneath which is a crust of red oxide, enveloping a nucleus of the original alloy. In certain cases bronze coins show a similar change. Mr. L. Fletcher has described an interesting case of the occurrence of piles of Roman coins at Chester, which had been buried for fifteen centuries, where the cavities between the piles were lined with crystals of red oxide and with blue and green carbonates of copper, associated with yellow carbonate of lead.f Professor Lacroix has described in like manner the alteration of old Roman coins from Algeria, where the metal has yielded cuprite, malachite and cerus- site.J In the thermal waters of Bourbonne-les-Bains, and at some other localities, crystals of cuprite have been found on some of the bronze objects which have been exposed for centuries to the action of the waters. The artificial production of cuprite was effected by Mitscherlich, by the slow reduction of a solution of copper sulphate through the agency of organic matter. It is believed that a similar de-oxidation may be effected by means of ferrous compounds, and a simple ex- planation is thus afforded of the possible formation, in certain cases, of the natural oxide. Melaconite. (Nos. 227, 228.) Cupric oxide in its native condition i^ known as Melaconite, and occurs usually as a dull earthy pulverulent substance, coating other copper-ores from which it may have been derived. In No. 228 it encrusts chalcosite. Crystals are extremely rare, and the crystal- lised specimen No. 227 is interesting as having been obtained from * " A Description of the Red Oxyd of Copper, the Production of Cornwall and of the Varieties in the form of its Crystal, with Observations on the Lodes which principally produced it ; and on the Crystallization of the arseniated Iron." By William Phillips. Trans. Geolog. Soc., vol. i. (1811), p. 23. f " On Crystals of Cuprite and Cerussite resulting from the slow alteration of Buried Coins." By L. Fletcher, M.A. Min. Mag. y vol. vii. (1887), p. 187. J Bull. Soc. Min. Fr., tome vi. (1883), p. 175. 44 MINERALS OP CORNWALL AND DE^ON. Mr. Tailing, and being the counterpart of the material studied by Prof. Maskelyne, who described the crystals forty years ago.* They belong to the monoclinic system. These crystals were analysed by Professor Church, who was the first to call attention to their occurrence.")* The substance termed Hack copper ore, which occurs in the gozzan of many copper lodes, is a more or less impure form of melaconite. This black ore was known to old Cornish miners as poder a word which De la Beche suggests may be a corruption of the word " powder," applied to the ore in consequence of its pulverulent character. J The value of this substance, so unattractive to the eye, was for a long time ill understood, and according to Pryce a quantity representing several thousand pounds in value was washed into the sea from Old Pool Mine. Crystalline scales of cupric oxide occur on Vesuvian lavas, and are known mineralogically as Tenorite. There they are no doubt formed by sublimation, whilst in copper-lodes the mineral results from the alteration of copper-ores, such as chalcosite, with which it is often associated. Native Copper. (Nos. 229 to 244.) Native copper, known to miners as virgin copper or malleable copper, occurs to a greater or less extent in almost all the copper mines of Cornwall. It is usually found in the upper or gozzany part of the lode, where it has evidently been formed as a secondary product by the reduction of certain cupriferous compounds. Rarely, if ever, in well defined crystals, it often assumes dendritic and arborescent forms, spreading out in picturesque branches, or expanding in thin laminae, or shooting out in delicate filaments like moss. Some of the branches are aggregates of small distorted crystals. The character- istic association of native copper with cuprite is illustrated by Nos. 221-224. Copper is reduced with such facility from solutions of its salts, especially the sulphate, that the formation of native copper presents no difficulty. In old mine workings, metallic copper may be readily precipitated from cupreous waters by means of metallic iron ; and in this way such objects as iron chains, bolts and nails will readily throw down cement copper. Decomposing organic matter is also an agent of reduction, and hence decaying wood frequently determines the local precipitation of the metal. Mr. W. H. Baker has described the occurrence of crystals of native copper on mine timber at the Kawan Mine, in New Zealand, found on re-opening the workings after they had been closed for twenty years. Some instructive examples of metallic copper formed around wood and iron objects, in old mines, will be found in Wall-case 35. * " On Crystals of Melaconite, and on Tenorite." By Prof. Maskeljne, M.A. Brit. Assoc. Rep., 1865, p. 33. f Chem. News, Mar. 17, 1865. p. 122. J Rep. Oeol. Cornwall, p. 591. NATIVE COPPER, ETC. 45 Native copper may also be reduced from cupreous solutions by natural electrolytic action, or by the influence of deoxidising media, like metallic sulphides, or even magnetite. Probably ferrous sul- phate has been in many cases the reducing agent. It has been shown that the conditions under which ferrous salts may be oxidised with deposition of metallic copper are precisely those which obtain in the circulation of underground waters.* Pseudomorphs of native copper having the form of octahedral crystals of cuprite are well known. The copper is in a spongy con- dition, through loss of matter, and has probably been formed by the action of weak sulphuric acid, which would give rise to cupric sul- phate and free copper.f A similar reaction may have been respon- sible for the origin of large masses of native copper. On the contrary, native copper may give rise to cuprite and other oxidised compounds, by exposure to meteoric influences. Metallic copper, in its natural condition is, however, very slowly affected by oxidising agencies. The specimen No. 248 shows native copper embedded in the serpentine of the Lizard district, in south-western Cornwall. In the Hall of the Museum are some very large masses of native copper from a mine at the Ghostcroft, Mullion, where it occurred near the junction of the serpentine with hornblende schist. These were exhibited, with some still larger specimens, in the Great Exhibition of 1851. f In the well-known copper-deposits of Monte Catini, near Florence, the ore occurs in connection with masses of serpentine and gabbro. The commonest mineral is copper-pyrites, but this in some parts passes superficially into erubescite, chalcosite and native copper. The Tuscan serpentine has been regarded as an altered cupriferous peridotite. According to B. Lotti^ the ores may have resulted from the differentiation of a strongly basic eruptive magma, rich in mag- nesium a view supported by Vogt.JI Copper is a metal much more widely distributed in nature than tin. Its ores occur not only in igneous rocks of acid type, like those which carry tin ore, but also and perhaps more frequently in basic eruptive rocks. Malachite and Chessylite. (Nos. 245 to 252.) Any body of copper ore, on exposure to meteoric activities, is apt to become more or less altered to the condition of carbonate. The * " The Deposition of Copper by solutions of Ferrous Salts." By H. C. Biddle. Journ. Geol. (Chicago), vol. ix. (1901), p. 430. t Cu. 2 O + H 2 S 4 = Cu + CuS 4 + H. 2 O. With respect to precipitation in the zone of weathering, see W. H. Weed : " The Enrichment of Gold and Silver Veins." Trans. Amer. Inst. Min. Eng., vol. xxx. (1901), p. 424. J On the Lizard copper, see F. J. Stephens. Trans. R. Geol. Soc. Corn., vol. xi. (1895), p. 680. " Sulla genesi dei giacimenti metalliferi nelle roccie eruttive basiche." BM. d. R. Com. Geolog. d' Italia, vol. xxiv. (1893), p. 343. 1 1 " Beitrage zur genetischen Classificationen der durch magmatisehe Differcntiationsprocesse und den durch Pneumatolyse entstandenen Erzvor- kornmen.'' Ze.it. f. prakt. Geol., Oct. 1894, p. 381. 46 MINEEALS OF CORNWALL AND DEVON. brilliant colours of the carbonates of copper render them conspicuous on the back of the lode. Specimens are here shown of the green carbonate or Malachite (Nos. 246 to 248) and of the blue carbonate or Chessylite, known also from its colour, as Azurite (Nos. 250-252). These related minerals are often associated, as in No. 250. The Cornish specimens usually occur as encrustations, sometimes fibrous but rarely crystallised. The delicate green fibrous malachite in No. 218 comes from South Caradon, near Liskeard. The crystals on No. 251 show chessylite in a pseudomorphous form, replacing crystals of the arsenate called clinoclase. The recent formation of carbonate of copper is illustrated by No'. 245, which is a sample of a material raised at one time as an ore at Wheal Leisure, near Perranzabuloe. This consists of grains of sand, with pebbles and recent shells, cemented by copper- ore, chiefly green carbonate, which is known to have been formed in the course of fifteen years by the action of rain-water percolating through the waste heaps of an old mine. This specimen was presented, with others, by the late Sir Warington Smyth, F.E.S. Of a somewhat similar character is the specimen, No. 246, re- cently obtained by Mr. J. B. Hill, of the Geological Survey, in which green carbonate of copper of recent formation is associated with shelly sand from Carbis Bay. Malachite and chessylite are usually described as hydrated carbon- ates, but as the water is not expelled until the minerals are exposed to a high temperature it may be assumed that the water is consti- tutional, the hydroxyl acting as a base ; hence the minerals are really basic carbonates. Chrysocolla. (Nos. 253, 254.) Copper may appear as a silicate wherever copper ores are exposed to the action of siliceous solutions. The copper silicate known as Chrysocolla presents a bluish green colour, with an opaline lustre, and is usually found in botryoidal or encrusting masses. The speci- mens here shown are well-defined crystals of cuprite, converted superficially into chrysocolla, with retention of perfect form. Chrysocolla seems in all cases to -be an amorphous product of the alteration of other copper ores, and the form presented by these specimens is of course pseudomorphous. Chdcanthite. (Nos. 255, 256.) Although sulphate of copper must be a very common product of the oxidation of copper sulphides, its ready solubility in water renders it unfit to survive, as a mineral, amid the damp surround- ings of a mine. It is, therefore, only under rather exceptional con- ditions that the solid salt is found in nature. As a mineral, the cupric sulphate is known as Chalcanthite or cyanosite. The specimens here exhibited show the beautiful blue colour which has led to the common name blue vitriol. In one of the specimens the salt exhibits LANGITE, WOODWARDITE, ETC. 47 a fibrous structure, whilst another shows the mineral in small sharply- defined anorthic crystals, seated on killas. The burrows, or heaps of old mine-refuse occasionally contain chalcanthite. A solution of sulphate of copper draining through a mineral vein furnishes a ready means for migration of the copper. It is probable that such cupreous solutions, descending to lower levels, may effect the secondary enrichment of many copper lodes by furnishing material from which copper sulphides may be precipitated, as pointed out by Mr. S. F. Emmons and Mr. W. H. Weed in the papers already cited (p. 35). Langite, Woodwardite, etc. (Nos. 257 to 266.) The beautiful mineral Langite is a basic cupric sulphate, described in 1864 by Prof. N. S. Maskelyne, who detected it on specimens sent to the British Museum by the late Mr. Tailing.* It occurs on killas and on a quartzose veinstone, in the form of minute blue crystals belonging to the orthorhombic system : it is found also as an in- crustation and as a cementing medium in a breccia of killas. Mr. Collins gives its localities as Copper Hill Mine and Wheal Bassett, Redruth ; and East Pool, Dolcoath and other mines near Cam- borne, f Langite was so named by Prof. Maskelyne in compliment to Prof. Viktor von Lang, of Vienna, who was at one time an officer in the mineralogical department of the British Museum. Lydlite is Maskelyne's name for a somewhat similar mineral, which Pisani called DevUline (No. 262)4 It was pointed out by Maskelyne and Flight that solutions of sulphate of lime or magnesia reacting on malachite might give rise to a basic cupric sulphate like langite. Closely associated with langite is another mineral which Prof. Maskelyne described at the same time under the name of Wariny- tonite a name given in honour of the late Sir Warington W. Smyth, who was for many years lecturer on mineralogy and mining at the Royal School of Mines, and in that capacity had charge of the mineral collections in this Museum (6. 1817, d. 1890). Under the name of Woodwardite Professor Church described, in 1866, a Cornish mineral which he found to be a hydrated cupric- aluminium sulphate.|| The specimen shown here presents the mineral in the form of a thin crust having a peculiarly rippled * " Anew British Mineral." Phil. Mag., vol. xxvii. (1864), p. 316. f " A Handbook to the Mineralogy of Cornwall and Devon," 1871, p. 61. J Comptes Rendus, vol. lix.(1864), p. 813. Journ. Chem. Soc., [2] vol. ix. (1871), p. 2. Chemical News, vol. xxii., (1870) p. 259. |! " Chemical Researches on New and Rare Cornish Minerals, iv. A New Hydrated Cupric -aluminum Sulphate." Journ. Chem. Soc., [2] vol. iv. (1866), p. 130. 48 MINERALS OF CORNWALL AND DEVON. surface and a beautiful turquoise blue colour. The name was given in memory of Dr. S. P. Woodward, of the British Museum, the author of the well-known "Manual of the Mollusca " (b. 1821, d. 1865). The mineral has close relations to langite. No. 265 is a specimen of a stalagmitic mineral of recent formation, found by Sir C. Le Neve Foster at St. Agnes, and described as Enysite by Mr. J. H. Collins, who found it to be a basic sulphate of copper and aluminium.* Conndlite. (Nos. 267, 268.) The extremely rare mineral Conndlite is a hydrous sulphate- chloride of copper, which was first examined chemically by Prof. Connell,t after whom it was named by Dana. It occurs in delicate diverging fibres, of a fine Prussian blue colour, belonging to the hexagonal system. The crystallographic characters of the species have been described by Prof. Maskelyne, and the chemical by Prof. Penfield.J No. 268 is the specimen referred to by Greg and Lettsom, when they say : "In Mr. Turner's collection there is a specimen stated in the catalogue to be from Carharrack in St. Day." In Levy's catalogue of 1837 it is described as cuivre vdoute, without any reference to its composition. || The mineral is associated in this specimen with cuprite and a little mispickel, on a matrix of quartz. In the catalogue of the Rashleigh collection a collection recently acquired by the Royal Institute of Cornwall, through the generosity of Mr. Enys and others, and now exhibited in the museum at Truro there is a figure of connellite, described as " copper ore of an azure blue colour composed of needle crystals."^ About twenty years ago the mineral was found in the Camborne district and in Marke Valley, and its occurrence was described by Mr. W. Semmons.** It occurred in copper veins traversing killas, and was associated with cuprite, malachite, brochantite, etc. The crystals were described by Prof. Miersff and by Dr. C. 0. Trechmann.|J The somewhat similar mineral, termed by Prof.Penfield Spangolite, has been detected on Cornish specimens by Prof. Miers. * Min. Mag., vol. i. (1877), p. 14. f " On Sulphato -chloride oi Copper anew mineral." Brit. Assoc. Rep., 1847, part ii., p. 49. % " On Connellite from Cornwall, England."- Amer. Journ. Sc., [3] vol. ad. (1890), p. 82. Manual of the Mineralogy of Great Britain, etc., p. 347. j| Vol. iii., p. 100, No. 4. *|j " Specimens of British Minerals selected from the Cabinet of Philip Rashleigh." Part ii., 1802, p. 13, PI. xii., fig. 1. ** " Notes on a recent Discovery of Connellite." By W. Senimons. Min. Mag., vol. vi. (1886), p. 160. tt Ibid., p. 167. 1+ Ibid., p. 171. '*" Spangolite." By H. A. Miers, M.A. Min. Mag. vol. x. (1894), p. 273. ATACAMITE. 49 Atacamite, etc. (Nos. 269 to 272.) In certain parts of the world the chlorides of copper have played at times an important part in the production of copper, but in Corn- wall they occur only as great rarities. Atacamite, the oxychloride, which is the best known member of the group, finds no place among the British minerals described in Greg and Lettsom's standard work. Indeed, it was not recognised as a British species until recorded by Prof. Church in 1865. The specimens show the mineral in minute crystals (No. 270), as an incrustation and in the form of tubular stalactites (No. 269). In some places atacamite may have been formed by the action of salt-water on oxides of copper, as pointed out by Mr. Cloud with reference to the famous occurrence at Wallaroo in South Australia.* The specimens here shown are from Botallack Mine, close to the sea ; but chlorides may also be formed inland, since rain water usually contains more or less salt. The infiltration of sea-water into a part of Botallack Mine was no doubt responsible for the formation of the cupric oxychloride which Prof. Church described as Botallackite, of which a specimen is seen in No. 271.f Tallingite (No. 272) is another mineral closely related to atacamite described by Prof. Church. J The name recalls the services of an observant collector, the late Mr. R. Tailing, who brought to light several new minerals from the West of England, and from whom a large number of the specimens here exhibited were originally obtained. * " Note on Atacamite." By T. C. Cloud, A.R.S.M. Chem. News, vol. xxxiv. (1876), p. 254. t " Notes on a Cornish Mineral of the Atacamite Group." Journ. Chem. Soc [2], vol. iii. (1865), p. 212. | " On some Hydrated Cupric Oxychlorides from Cornwall." Journ. Chem. Soc. [2], vol. iii. (1865), p. 77. 7882. E 50 MINERALS OP CORNWALL AND DEVON. CASE III. DIVISION 1. MINERALS OF CORNWALL AND DEVON. ARSENATES AND PHOSPHATES PROM THE COPPER GOZZANS. (Nos. 273 to 340.) The series of secondary minerals found in the gozzans of the copper lodes is continued in this Case by an extensive group of the arsenates and phosphates of copper. Many of the old mines of Cornwall were famous for these minerals, and the beautiful speci- mens here exhibited fully justify their reputation. Other examples as fine, or even finer, will be found in that part of the Ludlam collec- tion which is exhibited in the Hall. In the Cornish veinstones, arsenic seems to be more common than phosphorus, and it will consequently be observed that in this Case the arsenates form a grander show than the phosphates. The arsenic seems to have been originally brought up, in association with iron and sulphur, as arsenical pyrites. The species called mispickd has already been noticed (p. 31) and will again be referred to in connection with pyrites (p. 62). Mispickel contains theoreti- cally nearly half its weight of arsenic ; but even in ordinary pyrites, arsenic may be present in small proportion. The alteration which arsenical pyrites suffers in the oxidation-zone of a vein has no doubt furnished material for the formation of various arsenates. The mine -waters in Cornwall are known to be frequently arsenical. The original source of the phosphorus in the phosphatic minerals of the veinstone is perhaps not quite so obvious. It has, however, been probably derived, directly or indirectly, from apatite. This mineral, as already remarked (p. 24), is widely distributed in eruptive rocks, both acid and basic, but especially the latter. At a very early stage in the consolidation of the magma, the phosphorus separated as calcium phosphate, and the minerals which subsequently crystal- lised had to mould themselves around the pre-existing crystals of apatite. Hence the apatite usually appears as inclusions enveloped in the other rock constituents. It is true that in some cases, the apatite appears to offer much resistance to agents of alteration, and its crystals may remain fresh even when the surrounding matter has suffered more or less decompo- sition. But, on the other hand, apatite is known to be readily attacked by acids, even by water containing carbonic acid, and it has undoubtedly furnished phosphatic matter to the circulating waters, which would help to form metallic phosphates in the vein. Sulphuric OLIVENITE, LIBETHENITE, ETC. 51 acid, from decomposing pyrites in a vein, will readily attack apatite. Again, all surface water contains more or less calcium phosphate, probably derived, for the most part, from organic sources ; and, hence, surface drainage may carry phosphates into the shallow parts of a lode, and so give rise to reactions resulting in the formation of secondary phosphates as minerals of the gozzan. The chemical composition of the arsenates and phosphates has been the subject of prolonged researches by Prof. A. H. Church* ; and the subject has been taken up in recent years by Mr. G. J. Hartley.f Olivenite, Libethenite, etc. (Nos. 273 to 302.) It will be seen from the rather large series of specimens of olivenite (Nos. 273 to 296) that the olive green colour, which led Werner to name the species, is subject to much variation. Nos. 273 and 274 show brilliant crystals, belonging to the orthorhombic system, seated on brown iron- ore, so as to show their relation to the gozzan, and presenting a very dark green colour, inclining to black. Wood copper, or wood arsenate, is the name applied to the fibrous varieties, which often appear in delicate filaments, with a silky lustre, fre- quently of pale colour passing into ash grey or even white, and sometimes disposed in masses which present a velvet-like surface. Examples of the fibrous olivenite are exhibited in Nos. 290 to 296. Most of the olivenite here shown, as well as some of the other copper arsenates in this Case, came from Wheal Unity, in the parish of Grwinear. Mr. W. Semmons has remarked that " Wheal Unity was a perfect storehouse of copper minerals, no less than fourteen com- binations of that metal being found there. "J Olivenite is generally described as a hydrated arsenate, but the water is probably represented by hydroxyl, and the mineral may, therefore, be regarded as a basic arsenate of copper. Its formula, Cu ? (OH)As0 4 suggests its derivation from ortho-arsenic acid. The series of arsenates and phosphates are isomorphous||, and part of the arsenic in olivenite is consequently replaced in' many cases by phosphorus, without disturbance of crystalline character. When the replacement is complete, the resulting compound has the formula Cu 2 (OH)P0 4 . This constitutes the mineral known as Libethenite a mineral which owes its name to a locality in Hungary. In Corn- wall this phosphate is even more rare than olivenite. Specimens are shown as Nos. 297 to 302. In some of these examples the libethenite is crystallised on gozzany ironstone, and in others on malachite associations which in both cases recall the formation of the phosphate as a secondary mineral. * Journ. Ghem. Soc., various volumes from 1865. t " On the Constitution of the Mineral Arsenates and Phosphates." Min. Mag., vol. xii. (1900), pp. 120, 152, 223. J Min. Mag., vol. vi., p. 160. Se- Groth, op. cit., p. 89. i| Issmorphou,? substances are those which possess anilojy of chemical composition with close resemblance, or even identity of crystalline form. 7882. E 2 52 MINERALS OF CORNWALL AND DEVON. The rare phosphate of copper called Lunnite, or pseudo-malachite, is represented by Nos. 301, 302. Specimens from Botallack were analysed by Prof. Church.* Clinodase and Cornwallite. (Nos. 303 to 311). Clinoclase is a basic copper arsenate corresponding among the arsenates to pseudo-malachite among the phosphates. It occurs in dark greenish-blue crystals, referable to the monoclinic system, the name expressing the fact that the basal cleavage is inclined to the faces of the oblique prism. No. 304 shows the mineral in the form of a spherical mass, with curved cleavage-planes ; whilst Nos. 305 to 307 illustrate its characteristic occurrence in dark blue fibres aggregated in diverging and stellate groups. The very rare mineral, Cornwallite is a hydrated basic arsenate of copper, occurring in small botryoidal masses. Its composition has been determined by Prof. Church. "j" and the specimen here exhibited as No. 309 is interesting as being a portion of the specimen which he analysed. Other examples of cornwallite are shewn in Nos. 310, 311. The Cornish arsenates of copper were studied in the beginning of the last century by the Comte de Bournon, who was led to remark that " Nature has established very remarkable differences between the arseniates of copper.''^ The justice of this remark will be admitted by the visitor who, sweeping his eye over the minerals in this Case, contrasts the superficial characters of such species as olivenite, clinoclase, liroconite and chalcophyllite. Liroconite. (Nos. 312 to 321.) From all other copper arsenates the species termed liroconite is usually distinguished by its beautiful sky-blue colour. The mineral occurs in sharply defined crystals, belonging to the monoclinic system, and the old name octahedral arseniate of copper was intended to indicate their general shape. This species differs from the arsenates previously noticed, inasmuch as it contains aluminium as an essential constituent : it may be regarded in fact as a hydrated basic arsenate of copper and aluminium. It seems to have been found only in Wheals Unity, Gorland and Muttrell, in Gwennap ; and, as some of the specimens here show, it was found with other oxidised products in the gozzany part of the veinstone. Some exceptional specimens of this species are included in the Rashleigh collection now in the museum of the Royal Institution of Cornwall at Truro. * Journ. Chem. Soc. [2], vol. iii. (1865), p. 2. t Journ. Chqrn. Soc., [2] vol. vi. (1868), p. 276. J "Description of the Arseniates of Copper and of Iron, from the county of Cornwall." By the Count de Bournon. Phil. Trans., vol. xci. (1801), p. 169. CHALCOPHYLLITE, ETC. 53 Chalcophyllite. (Nos. 322 to 328.) The rare and beautiful mineral called Chalcophyllite, known also as Tamarite from its occurrence at Wheal Tamar, is represented by a series of excellent specimens. It crystallises in the hexagonal system, and the crystals usually assume a tabular habit, as well seen in most of the examples here exhibited. The six-sided plates present perfect basal cleavage, whence the name copper mica, sometimes applied to this species. The shape and the fine emerald green colour give the mineral in some cases a certain resemblance to " uranium mica," or torbernite (p. 82). Chalcophyllite has generally been regarded as a hydrated basic arsenate of copper and aluminium, but the analysis of a Cornish specimen, carefully separated from foreign matter, by Mr. E. G. J. Hartley, has revealed the presence of a sulphate.* Some of the specimens here exhibited show the Chalcophyllite associated with chalcopyrite, and others with decomposing mis- pickel, thus betraying the origin of the mineral. In No. 328 the substance seems partially altered to chrysocolla. Bayldonite, etc. (Nos. 329-331.) Under the name Bayldonite, in honour of Dr. John Bayldon, at one time Professor in the Royal Agricultural College at Cirencester, Prof. Church described, some forty years ago, a new species, which occurs as a concretionary mineral of green colour, seen in Nos. 329 and 330, where it coats a gozzany quartzose veinstone. This species is a hydrated basic arsenate of copper and lead.f No. 331 is a specimen of Chenevixite, which is a hydrated basic arsenate of copper and iron, occurring as a dull greenish amorphous substance on a quartzose matrix. Andrewsite, Chalcosiderite, etc. (Nos. 332 to 340.) Andrewsite is a mineral described in 1871 by Prof. Maskelyne, and named after the late Dr. T. Andrews of Belfast. J It occurs in small bluisi -green globular masses, with a radiate structure, as shown in No. 332. Sir C. Le Neve Foster described its occurrence at Wheal Phrenix Mine, near Liskeard, where it is found in a tin-lode in granite, carrying much limonite and a little copper glance and cuprite. $ A bright green mineral occurring with the Andrewsite of Wheal Phoenix was referred by Prof. Maskelyne to Ullmann's species * " Communications from the Oxford Mineralogical Laboratory." Min. Mag., vol. xii. (1900), p. 120. See also Prof. Church in Journ. Chem. Soc. [2] vol. viii. (1870), p. 168. f Journ. Chem. Soc. [2], vol. iii. (1865), p. 265. J " On Andrewsite." Brit. Ass. Rept. for 1871, p. 75. Journ. Chem. Soc. [2] vol. xiii. (1875), p. 586. " On Andrewsite." Trans. R. Oeol. Soc. Corn., vol. ix. (1875), p. 163, 54 MINERALS OF CORNWALL AND DEVON. Chalcosiderite* It crystallises in the anorthic system, and the speci- mens Nos. 333 to 336 show crystals seated on a gozzany matrix. Both chalcosiderite and andrewsite are hydrated phosphates of iron a'nd copper. A trace of uranium has been found in chalcosiderite. Henwoodite, from the same mine, is a mineral named by Mr. J. H. Collins after Mr. W. Jory Kenwood (6. 1805, d. 1875). It occurred in small globular masses of a turquoise blue colour on limonite, and seems to be a hydrous phosphate of copper and aluminium.f Its characters are well seen in Nos. 337 to 340. DIVISION S, MINERALS OF CORNWALL AND DEVON. ORES OF LEAD, ZINC, ANTIMONY, ETC. (Nos. 341 to 408.) Whilst the tin- and copper-lodes of Cornwall and Devon generally run in a direction which may be roughly set down as nearly E. and W. or N.E. and S.W., those veins which carry lead often take a course nearly at right angles to this direction. Such veins are therefore known as " cross-courses." Many of these cross veins are quite unproductive of ore, whilst others are richly plumbiferous. The N. and S. veins are usually of later date than those which hold an E. and W. course, as attested by the fact that the former may in some cases be seen to cut across and dislocate the latter. The intro duction of the lead-ore, probably by means of thermal waters, seems to have been effected subsequently to the deposition of the minerals of the tin-copper lodes. Lead-ore is not confined, however, to the cross-courses, but is sometimes found in the veins which have a bearing more or less approximately east and west. The ore of lead is not infrequently associated with copper-ore, but very rarely indeed with tin-ore. The typical lead-lodes are in killas, and in certain cases at a considerable distance from granite ; some of the most productive mines having been in the eastern and northern divisions of Cornwall and the adjacent part of Devonshire, and some even in North Devon. The ore is normally galena, or lead sulphide, and the matrix fre- quently contains fluor-spar. At the present time but little lead-ore is being raised in Cornwall and none in Devon ; and a similar remark applies to zinc-ore, though some of the old burrows, or waste-heaps, may be worked over for sake of the blende. Ores of zinc frequently accompany those of lead. The zinc usually occurs as sulphide, or zinc blende, and in Cornwall this mineral is rather widely diffused, often in association with lead-ore and not infrequently with copper-ore, though only occasionally with tin. * " On Andrewsite and Chalkosiderite," Journ. Chem. Soc., [2j vol. xiii. (1875), p. 586. t Min. Mag., vol. i. (1877), p. 11. LEAD-ORES. 55 Antimony has been yielded from time to time by many Cornish mines, especially in the northern part of the county, where the killas is remote from granite, but associated in places with greenstone. Up to a recent date small quantities were obtained from this district, but at the present time none is being worked. Galena, Cerussite, and Pyromorphite (Nos. 341 to 380). In Cornwall and Devon, as in most other lead districts, the common ore of lead is the sulphide, known as Galena, a mineral which crys- tallises in the cubic system, and admits of perfect cubic cleavage. Some excellent examples of crystallised galena are here exhibited, the cubo-octahedra* of Nos. 343 and 346 being characteristic crystals of this species. But as a larger series of specimens of galena crystals will be found among the minerals from the lead districts of the North of England (pp. 137, 102) no detailed notice is needed in this place. Many of the specimens here exhibited illustrate the paragenetic relations of galena in the S.W. of England. Chalybite, or ferrouscar- bonate, is a characteristic companion of galena, and the two minerals may be seen together in Nos. 343 and 345 ; blende, or zinc sulphide, is another common associate, as shown in No. 348 ; whilst pyrite, or iron sulphide, is very widely distributed in the lead veins as in the other lodes, and its relation to galena is seen in Nos. 348, 349, 359. With regard to the sparry minerals of the lead veins, the specimens show quartz (345, 349, 354, 359), calcite (349, 357), fluor-spar (351 to 386) and pearl-spar (354). Many of the fine specimens of fluor and galena are from the old silver-lead mines of Beer Alston, in South Devon, which were worked on two great cross courses, or north and south veins, and were once the centre of great mining activity. The specimen, No. 360, from Wheal Hope, near Truro, shows the well-known pseudomorphous galena sometimes called blue lead ore Here the lead sulphide has gradually taken the place of six-sided prismatic crystals of pyromorphite, or lead phosphate. Such pseudomorphs are, in some cases, hollow, the outer portion of the crystals having been converted into galena, and the enclosed pyro- morphite having then been removed in solution. The formation of a sulphide after a phosphate suggests rather exceptional reactions inasmuch as the sulphides are generally of earlier formation than the oxidised compounds of the metal. Galena readily suffers alteration in the shallow part of an ore- deposit, where the sulphide is exposed to oxygen and carbonic acid, and the most common product of alteration is the carbonate of lead, called Cerussite. Examples of this mineral are shown in Nos. 361 to 369. Most of the specimens still retain sufficient of the gozzany matrix to attest the superficial origin of the mineral. The * A cubo -octahedron is a combination of the two simple forms, the cube and the regular octahedron. 56 MINERALS OF CORNWALL AND DEVON. cerussite occurs chiefly in long slender crystals, often acicular and sometimes of great delicacy, and these by their snow-white colour contrast strikingly with the dark brown limonite on which they are displayed. Many of the finest examples are from the old Pentire Glaze Mine, in the parish of St. Minver, in North Cornwall. A splendid specimen of cerussite from Frank Mill's Mine, Christow, near Exeter presented many years ago by C. Wescombe, Esq., is exhibited in a neighbouring pedestal-case opposite Wall-case No. 18. The isomorphous series of phosphates, arseno -phosphates and arsenates of lead, constituting the minerals known as Pyromorphite and Mimetite, receive ample illustration here (Nos. 370 to 380). Cornwall formerly yielded remarkably fine specimens of these species, and many of the examples in this case came from the old mine of Wheal Alfred, in the parish of Phillack, in West Cornwall a mine which in its day had great reputation for such specimens. The crystals belong to the hexagonal system, and usually affect a prismatic habit. They exhibit green, yellow and brown colours with a lustre which, in some cases, is rather resinous, and in others almost adamantine, as is so often the case with minerals containing lead. The phosphate or arsenate is associated in pyromorphite and mimetite with lead chloride. The origin of these species is probably to be sought in the alteration of mispickel and apatite, which has furnished, directly or indirectly, the acid radicles to the lead of the galena. Like the phosphates and arsenates of copper shown in the opposite division of this Case, these lead salts are essentially the products of chemical reactions carried on in the laboratory of the gozzan. Silver ores (Nos. 381 to 390). Most of the galena of Cornwall and Devon is more or less argenti- ferous, and some of it extremely rich. According to Pryce the ore raised at one time at Garras, near Truro, yielded lead which gave as much as 100 ounces of silver to the ton. The rich argentiferous galena of Beer Alston, in Devonshire, contained from 80 to 120 ounces of silver to the ton of lead, the proportion in one case rising to 140 ounces. It is probable that the silver in galena occurs as a sulphide, and since the two sulphides, Ag^SandPbS, possess similar crystallographic symmetry they may be associated as isomorphous growths. In some cases, however, they seem to occur rather in the state of mere mechanical mixture, for it has sometimes been found that the galena becomes much less argentiferous after the ore has been well washed.* Sulphide of silver, forming the mineral known as Argentite, has been found, though rarely, in Cornwall. The mineral crystallises in the cubic system, and the finest British specimens occurred at Wheal Ludcott, an abandoned mine near Liskeard, where the cross course yielded cubo-octahedra measuring half an inch along the edge. * J. A. Phillips in Journ. Soc. Arts, April 27, 1859 r SILVER-ORES. 57 ifc is from this mine that No. 381 was obtained. No. 382 is a specimen of Pyrargyrite, or dark red silver-ore, a sulphantimonite of silver, of rare occurrence in Britain. This specimen came also from Wheal Ludcott. The late Mr. Thomas Davies of the British Museum, described the occurrence of Stephanite at this mine the first recorded occurrence of crystals of this species in Britain.* This mineral is likewise a sulphantimonite of silver, and was found at Wheal Ludcott, associated with argentite and native silver. Far finer specimens, however, were afterwards obtained from Wheal Newton, near Callington a mine which yielded the magnificent crystal preserved under a glass shade in Wall-case No. 14. This specimen was the subject of a memoir by Prof. W. J. Lewis. | In the early part of the last century, silver-ore was discovered in quantity in a cross-course at Wheal Herland, near Gwinear.J About 108 tons were extracted from a depth of between 110 and 142 fathoms. The minerals included galena, argentite and native silver, with bismuth and cobalt ore. Small veins, rich in argentiferous galena and occasionally carrying true silver-ores, have been worked at Duchy Peru in Perranzabuloe. The veins are cross-courses, running north and south, and inter- secting the great iron- lode, most of the silver- ore being found near the intersection.^ According to Mr. Joseph Game, the first discovery of silver in Cornwall was made about 1788, in a mine in the parish of Perran- zabuloe, " which was in consequence dignified with the name of Huel Mexico."|| Dolcoath and Wheal Duchy, near Callington, are other mines which have yielded silver-ore in commercial quantity, the latter mine having produced native silver, argentite and red silver ore, or pyrargyrite. Silver in a free or native condition has not infrequently been found in Cornish mines, but usually in only very small amount. Several examples of Native Silver are here shown (Nos. 383 to 386). The silver is mostly in a capillary form, in thin hairs or stiff wire, often twisted, and occasionally like " moss copper." It is invariably a secondary mineral, and may have been reduced from the state of sulphide or deposited from silver salts in solution. Prof. Vogt, who has carefully studied the occurrence of native silver at the famous mines of Kongsberg in Norway,^f believes that direct crystallisation * Geol. Mag., vol. iii. (1866), p. 432. t " On a Crystal of Stephanite from Wheal Newton." Proc. Camb. Phil. Soc., vol. iv. (1883), p. 240. + " Account of the Discovery of Silver in Herland Copper Mine." By the Rev. Malachy Hit-chins. Phil. Trans., vol. xci. (1801), p. 159. " The Duchy Peru Lode, Perranzabuloe." By Warington Smyth, M.A., F.R.S. Trans. E. Geol Soc. Corn., vol. x. (1887), p. 120. || Trans. R. Geol. Soc. Corn., vol. i. (1818), p. 121. ^| " Ueb^r die Bildung des gediegenen Silbers, besoncbrs dos Kongsberger Silbcrs durch Secundarprocesse aus Silberglanz und anderen Silbererzen." J. prakt. Geol, April, 1899, p. 113. 58 MINERALS OF CORNWALL AND DEVON. from solution is not common, and that the metal has usually passed through the condition of sulphide. Much of the capillary silver in the Cornish veins may possibly have been derived, like the similar forms of native copper, from circulating solutions, through the reducing action of ferrous salts or perhaps metallic sulphides. Haloid combinations of silver are often found native, and in Corn- wall the chloride has been recorded from a number of localities. This compound is known commonly as horn silver, and technically as Cerargyrite names suggested by the soft and sectile character of the substance, which can be cut as readily as a piece of horn. It crystallises in the cubic system, and is usually found as an incrusta- tion on other minerals. In most of the specimens shown here (Nos. 387 to 390) the cerargyrite is spread over an ochreous matrix, thus testifying to its superficial formation as a mineral of the gozzan. Although rather unattractive to the eye, the mineral is one of the first importance among silver ores, inasmuch as it contains when pure three-quarters of its weight of silver. In Cornwall, however, it occurs generally in only small quantity, but at the present time (1904) a deposit of silver ore, chiefly cerargyrite, is being worked, in a north and south vein, at the Perran Mines, Marazion. No. 387 is a sample of this ore, presented by G. D. McGrigor, Esq. Zinc-ores : Blende and Calamine (Nos. 391 to 403). As " blende " is a name of rather general significance applied to several minerals, the sulphide of zinc, which is the commonest of all blendes, is termed for distinction's sake zinc blende. The name Sphalerite, given to it half a century ago by Haidinger, has been revived in recent years, and is now frequently used in place of " blende." By miners in Cornwall, as elsewhere, it is often known as Black Jack. As the number of Cornish specimens of blende shown here is not large, and as the mineral will come prominently forward in con- nection with the products of the North of England, but little need be said in this place with reference to its characters. It crystallises in the cubic system, has usually a dark brown colour, and presents a brilliant lustre. All these characters are illustrated by Nos. 391 to 399. In No. 392 the black blende is crystallised around slender prismatic crystals of white quartz. Chalybite is associated with the zinc ore in No. 400. The iron-bearing variety of blende from St. Agnes, called Marmatite^ is seen in No. 402. Instead of being crystallised, the blende of Nos. 397 and 401 is in mammillary forms ; whilst No. 401 is also exceptional in presenting a white colour. By exposure to meteoric agencies the sulphide of zinc may become altered to carbonate thus forming a substance sometimes known to mineralogists as Calamine. No. 403 is an example of Cornish calamine. It is not, however, a common mineral in Cornwall and Devon ; but the visitor will find it prominent among the ores of the Mendip Hills and of Derbyshire, and further description may, therefore, be deferred until these ores fall under notice (pp. 10<), 141). ANTIMONY-ORES. 59 Antimony ores (Nos. 404 to 408). Antimony a metal which forms with arsenic and bismuth an alliance of brittle metals occurs in nature usually as a sulphide, forming a mineral known variously as Stibnite, antimonite, grey antimony ore or antimony glance. In some of the cross veins which course in a north and south direction through the killas of north- eastern Cornwall, especially near Padstow and Tintagel, this mineral was at one time not by any means infrequent. The specimen No. 404 is from Endellion. The Cornish stibnite is either massive, fibrous, or in inconspicuous crystals. From such specimens it is refreshing to turn to the noble crystals of this species, which startled mineralogists when they were first brought some years ago from Japan. Of these Japanese crystals a fine example is exhibited in a neighbouring Case, sufficiently illustrating their remarkable size, form and lustre. In the antimony-bearing veins of Cornwall the metal occurs not only combined with sulphur as stibnite, but associated also with sulphide of lead. The mineral so formed was named by Haidinger, Jamesonite, after Robert Jameson who was for so many years pro- fessor of mineralogy in Edinburgh (6. 1774, d. 1854). The specimens 405 to 407 show this species as a fibrous substance of steel -grey or iron-black colour and metallic lustre, not altogether unlike fibrous stibnite. It may be regarded as a sulph-antimonite of lead, or as a double sulphide containing, according to Rammelsberg, 2PbS. Sb L S .,, having therefore the formula of galena and stibnite.* The yellow amorphous mineral in No. 408 is a hydrous lead anti- nionite, known as Bindheimite or Bleinierite. It is evidently an oxidation product resulting from the alteration of Jamesonite, with which it is often associated, as seen in Nos. 400 and 407, where the metallic mineral is partially encrusted with the yellow antimonate. * Ses. however, a paper by Mr. L. J. Spencer and Mr. G. T. Prior, in Min. Mag., vol. xii. (1900), p. 58. 60 MINERALS OF CORNWALL AND DEVON. CASE IV. DIVISION I, , MINERALS OF CORNWALL AND DEVON. SULPHIDES AND SULPHO -SALTS. (Nos. 409 to 475). Several metallic sulphides including those of tin, copper, lead, zinc and antimony have been already noticed in the descriptions of Cases I. to TIL, in which they are exhibited. A few other sulphides, such as iron pyrites, with certain sulpho-salts, are grouped together in the Case now under description. Iron-pyrites, the most widely diffused of all metallic sulphides, is not peculiar to any particular type of ore deposit, and has therefore been left without special notice in the preceding pages. The sulpho-salts here exhibited include bournonite, tetrahedrite, and tennantite and as these species are found usually in lead -veins, and contain antimony and arsenic, they stand in close relationship to the minerals exhibited in the Case immediately preceding (No. III.). Pyrite (Nos. 409 to 428). Pyrite is the name now frequently employed by mineralogists to designate the mineral which is commonly known as iron-pyrites. This species consists of iron disulphide, crystallising in the cubic system, and some very bold examples of the crystals are shown in this Case. In the mineral-veins of the West of England, pyrite is one of the commonest constituents, and is termed by the miners mundic. According to Borlase " the Cornish name is Mundic, from the cleanly shining appearance both of its surface and struc- ture."* Pyrite is a mineral widely distributed through most rocks, whether eruptive or sedimentary, in some cases as an original mineral, in others as a secondary product. As a vein-mineral its formation appears to have extended from the earliest to the latest stages in the history of the lode. In some cases the pyrite may be of primary origin ; in others it has been introduced at a later date, evidently deposited from solution on other minerals, encrusting or replacing them, as witnessed by such pseudomorphs as Nos. 426 and 427 ; and in yet other cases the pyrite may be of comparatively recent * " The Natural History of Cornwall." Oxford : 1758, p. 131. PYRITE. origin, due to the reduction of solution of a sulphate, though probably this mode of origin is not so common in veinstones as in sedimentary rocks. Stalactitic pyrite has occurred at East Pool. Nos. 414 and 415 show the pyrite crystallised on quartz, whilst in No. 410 the quartz has crystallised on the pyrite. In No. 425 pyrite has been deposited on large cubes of fluorspar, forming a brass-like coating with a drusy surface. No. 426 is a hollow epimorph of pyrite after calcite, and No. 427 one of pyrite after baryte ; the mineral originally invested having in both cases been completely removed, leaving a pyritous shell. * Pyrite commonly crystallises in cubes, as shown in Nos. 410, 415 and 416. In No. 410 the cubes measure more than an inch along the edge. The fine specimen No. 409 shows the regular octahedron in combina- tion with the cube. No. 413 is an excellent example of sharply defined crystals in form of the pentagonal dodecahedron, which is a hemihedral form of the four-faced cube, so characteristic of pyrite that it was called by Haidinger the pyritoliedron. A hemihedral form of the six-faced octahedron is known as the dyakis-dodeca- hedron, or diplohedron ; this is also characteristic of pyrite, but though occasionally occurring as an independent form it is usually found in combination. The " Pyrites group " consists of a few closely allied minerals, assuming these hemihedral forms ; and since each face of the pentagonal and the dyakis- dodecahedron has an opposite parallel face the group is said to present " parallel faced hemihedrism."f Most of the specimens exhibited in this Case show the brass-yellow colour of the pyrite, but in No. 419 the colour is steely grey. The metallic lustre is illustrated by most of the speci- mens, and in No. 414, where the pyrite is crystallised on quartz, the lustre is exceptionally brilliant. Occasionally the surface becomes coated with a brown tarnish due to superficial alteration into limonite. Such alteration may penetrate to a considerable depth, and ultimately the entire crystal may be converted into the brown iron oxide. This change one of the most common chemical changes which pyrite suffers is well illustrated by the specimen No. 428, in which an aggregate of cubes has been transformed more or less com- pletely into ferric hydrate with retention of the pyrite shape. The limonitisation of pyrite contributes largely to the formation of gozzan. Still more unstable than pyrite is the ortho -rhombic species of iron disulphide, known as Marcasite (No. 428). This mineral occurs occasionally in the Cornish veinstones, but is not usually abundant, and further reference to it is therefore deferred until the marcasite of the sedimentary rocks has to be described (p. 198). * An epimorph is a pseudomorph formed by the deposition of one mineral upon another ; and is therefore simply a mechanical encrustation. Epimorphs are known also as perimorphs. f See Prof Miers's " Mineralogy " (p. 49) for technical definition of the class of crystals known as the " Pyrite class," characterised by " tesseral centre -symmetry." 62 MINERALS OF CORNWALL AND DEVOV. A fine series of specimens of pyrite will be found in Case II. of the Ludlam Collection in the Hall of the Museum, and others in the Wall- case No. 46 on the Principal Floor. Mispickel (Nos. 429-436). Although Mispickd has already been noticed as an associate of tinstone (p. 31), it demands further reference in this place, as being an important member of the group of metallic sulphides known sometimes as the Pyritoids. In a pure state it is an arseno- sulphide of iron, conforming to the simple formula Fe As S, and therefore con- taining theoretically about 46 per cent, of arsenic. Hence it is known as arseno-pyrite or arsenical pyrite. Struck with the pick it emits the characteristic garlic -like odour of arsenic, and is recognised by miners as arsenical mundic or arsenical iron, or merely as " arsenic." Mispickel belongs to the orthorhombic system, like marcasite, with which it seems to be isomorphous. Many specimens, as Nos. 429, 430, show the rhombic prisms sharply denned, and some illustrate the characteristic twinning, similar to that of marcasite. The curvature of some of the faces is very marked in No. 429. The silver white and steel-grey colours of mispickel are fairly illustrated by Nos. 430, 434 ; but after exposure, though less prone to alteration than marcasite, the colour is apt to suffer. The bold crystals in No. 433 show a brilliant reddish tarnish : this specimen is from Wheal Kitty, St. Agnes, and the mineral is here associated with copper pyrites, coated with green carbonate, whilst chalybite, in globular aggregates of lenticular crystals, has been deposited on certain faces of the mispickel. Many of the specimens show the mispickel in association with quartz, in some cases well crystallised. The quartzose veinstone of certain specimens, as seen here, is of cavernous structure, with pseudomorphic hollows ; in other cases it is " peachy," that is to say, it is associated with chlorite. Copper-pyrites may be detected on several specimens. By the alteration of mispickel, through the action of oxidising agencies in the shallow parts of a lode, iron arsenates, like scorodite, may be formed (p. 73). When the arsenide is associated with copper ores, as is so often the case, as just mentioned, the resulting products of oxidation may be copper arsenates, or copper-iron arsenates, such as are illustrated by the fine display in Case III. The importance of mispickel as an "arsenic ore," or source of white arsenic, in the copper and tin mines of the West of England, has already been referred to, and statistics of production given, at p. 32. Bournonite (Nos. 437 to 456). More than a century ago, the beautiful mineral now called Bour- nonite was figured by Mr. Rashleigh in his work on the Menabilly Col- lection * a collection recently added to the Museum of the r * * Rashleigh's " Specimens of British Minerals," 179" PI. xix. figs. 1 and 2, p. 34. BOURNONITE. O.I Royal Institution of Cornwall at Truro. His specimens were obtained from Wheal Boys, in the parish of Endellion, in the killas country of North-east Cornwall. It was from this locality that the specimens here shown as Nos. 437 and 438 were derived. The mineral occurred there in association with zinc blende, jamesonite, chalybite, etc. Described by Rashleigh as "an ore of antimony" it was recognised as a distinct species by the Comte de Bournon, a French refugee living in this country in the early part of the eighteenth century.* By de Bournon it was called from its locality endettione, whence the name Endellionite, sometimes applied to this species. This name, however, has generally given place to Jameson's name bournonite, in recognition of the mineralogist who first described it with accuracy. The original specimens from Endellion were eclipsed by the much finer examples raised many years ago at Herodsfoot Mine, about seven miles S.W. of Caradon in East Cornwall. In this silver- lead mine, the lode ran through killas, with a bearing about 20 E. of north, and the argentiferous galena for which the mine was worked occurred in a quartz veinstone, where it was associated with pyrite, blende, occasional bunches of rich copper ore, and certain antimonial minerals. The antimony ore occurred just below the gozzan, and being detrimental to the lead was regarded as a nuisance.f An analysis of the Herodsfoot bournonite by Mr. C. E. Waitf showed that it conformed to the recognised formula Cu 2 Pb^Sb 2 S 6 , the antimony being replaced to a small extent by arsenic. It may be regarded as a sulphantimonite of lead and copper. Bournonite crystallises in the orthorhombic system ; and some noble crystals, remarkable not only for size but for complexity of form and brilliancy of certain faces, are exhibited in this Case. The crystallography of the Cornish bournonite has been exhaustively studied by Professor Miers.H Twin groups are very common, giving rise in some cases to cruciform, stellate and circular discs, which are known as cog-wheel-ore, as illustrated by Nos. 441, 442, 445 and 446. A hint as to the possible genesis of bournonite may be obtained from certain pseudomorphs having the form of tetrahedrite but the composition of bournonite, thus suggesting that under certain cir- cumstances bournonite may have been derived from the alteration of tetrahedrite. ^ ,* " Description of a triple sulphuret of Lead, Antimony and Copper from Cornwall." By the Count de Bournon, F.R.S. Phil. Trans., vol. xciv. (1804), p. 30. Also Analyses by Hatchett, Ibid., p. 63. f " On the Metalliferous Associations of the Liskeard Rocks." By Mr. John Giles. Trans. Roy. Geol. Soc. Corn., vol. vii. (1865), p. 198. % " Analysis of Bournonite." Cham. News, vol. xxviii. (1873), p. 271. This is equivalent to 2 PbS. Cu 2 S.Sb 2 S 3 . || " The Crystallography of Bournonite." By H. A. Miers, M.A., Min. Mag., vol. vi. (1884), p. 59. 64 MINERALS OF CORNWALL AND DEVON. Tetrahedrite and Tennantite (Nos. 457 to 475). Tetrahedrite is known sometimes as grey copper ore, but this term is ambiguous since it is also occasionally applied to copper glance. The name tetrahedrite refers to the regular tetrahedral form which the crystals usually present. Grand examples were obtained at one time from Herodsfoot Mine, where the mineral occurred in associa- tion with the bournonite just described. A fine suite of the Lis- keard tetrahedrites is here exhibited (Nos. 457 to 468). The regular tetrahedron is usually bevelled on the edges by planes of the three- faced tetrahedron. It will be noted that the crystals are coated in most cases with minute crystals of chalcopyrite, producing a rough drusy surface ; and that the chalcopyrite frequently displays a brilliant iridescence, due to superficial conversion into " peacock copper." When the mineral was first raisfed the colours were often gorgeous, but the effect became impaired by exposure. The encrusting copper- pyrites seems to have been derived from the alteration of the tetrahedrite. The chemical composition of tetrahedrite is very complicated, and the crystals are often wanting in homogeneity ; but it may be regarded as essentially a sulphantimonite of copper, in which the copper is partially replaced by iron, zinc or even silver, whilst the antimony is more or less replaced by arsenic. Recent analyses by Mr. G. T. Prior* have led to a new formula, which admits of simplest expression in the form Cu. Sb S. ; . Tetrahedrite is likewise known under the name of fahl ore a name borrowed from the German Fahlerz, which is now regarded as a general term applied not only to the copper sulphantimonite but also to the corresponding sulpharsenite. When arsenic is substituted for antimony, the mineral is called Tennantite. The old name fahl-ore consaquently includes both tetrahedrite and tennantite, with isomorphou^ mixtures of the two. In some tennantite bismuth is present. Tennantite received its name from a famous English chemist, Smithson Tennant (/>. 1761, d. 1815). The specimens Nos. 469 to 475, from Wheal Jewel in Gwennap, illustrate the characters of this mineral, and show its association with quartz and copper pyrites. Excellent crystals of tetrahedrite, having all the characteristics of the Cornish mineral, were found on the ancient Roman bronze coins which Daubree described, from the thermal springs of Bourbonne- les-Bains (Haute Marne). The alteration of the bronze yielded not only tetrahedrite, but also chalcosite, chalcopyrite and erubescite. No.476 is a specimen of Condurrite, a mineral described by Faraday, from the Condurrow Mine, Camborne. It is a black amorphous mineral, so soft as to soil the fingers. Chemically it is chiefly a copper arsenide, but seems to be a mixture rather than a definite species, and has been regarded as an alteration-product derived perhaps from tennantite. * " The Identity of Binnite with Tennantite ; and the Chemical Composi- tion of Fahlerz." By G. T. Prior, M.A., and L. J. Spencer, M.A. Min. Mag., vol. xii. (1900), p. 184 (Fahlerz, p. 193). ORES OF IRON. 65 DIVISION 2. MINERALS OF CORNWALL AND DEVON. ORES OF IRON, ETC. (Nos. 477 to 544.) Ores of iron enjoy a wider distribution than the ores of any other metal. They occur both in eruptive and in sedimentary rocks and are not restricted in the latter to any special horizon. Never- theless, in Cornwall and Devon, the accumulation of suitable minerals in the form of workable ore-bodies is rather limited ; and at the present time no iron ore is being raised in Cornwall, and only an insignificant quantity in Devonshire. Most of the fine specimens exhibited in this Case were obtained many years ago from the famous mine near Lostwithiel, which was known, after Queen Victoria's visit in 1846, as the Restormel Royal Iron Mine. The great iron lode, generally in two branches, is a cross course in killas, bearing about 15 W. of N., and having a dip to the east of between 70 to 85.* The branches formed practically two parallel veins, the principal lode being in some parts more than 20 feet wide. The ore was carried in a quartzose veinstone, which abounded in vugs or drusy chambers, often lined with beautiful crystals.f It was from the walls of such cavities that the specimens here exhibited were taken. The ore was chiefly ha-matite, with gothite and limonite, accompanied occasionally by black oxide of manganese and lithomarge, in small pockets. Extensive workings for iron-ore were also made in Cornwall on the Great Perran Lode, or the Duchy Peru lode, in Perranzabuloe. This vein extends for several miles in a direction which is approxi- mately W.N.W. and E.S.E., and has in some parts a width of as much as 120 feet. The lode courses through killas, and consists principally of a brecciated quartzose veinstone holding much chalybite, or carbonate of iron, which passes into brown iron-ore in the upper part and is associated with large quantities of zinc blende and a little copper-ore. J Both in this lode, and in the Restormel iron-lode, pseudomorphous quartz is abundant, testifying to the chemical changes which must have been rife since the original formation of the veins. Magnetite (No. 477). Two anhydrous oxides of iron occur native one called magnetite (Fe 3 4 ), comparatively rare in this country ; the other termed haematite (Fe 2 3 ), fairly abundant, and in the North of England largely worked as an ore. * Henwood, Trans. R. Geol. Soc. Corn., vol. v. (1843), p. 128. f A drusy surface is one coated with small crystals. A cavity lined with crystals is known as a druse ; or if rounded it is often termed a geode. See Sir W. W. Smyth's papers, " On the Iron Mines of Perran." Trans. R. Geol. Soc. Corn., vol. vii. (1865), p. 332 ; and " The Duchy Peru Lode, Per- ranzabuloe." Ibid. vol. x. (1887), p 120. 7882. F 66 MINERALS OF CORNWALL AND DEVON. Magnetite occurs as a constituent of nearly all eruptive rocks and is especially notable in the dark-coloured dense rocks of basic type. It must have separated from the molten magma in most cases, at an early phase in the consolidation, for it occurs as enclosures in nearly all the other rock constituents. This priority of crystallisa- tion, however, was not invariable ; and Dr. Teall has shown, for example, that in some of the basaltic rocks of Franz Josef Land the magnetite was the last mineral to crystallise.* Whilst magnetite is thus abundant in microscopic crystals and grains, it is by no means common, in this country, in macroscopic crystals. No. 477 shows, rather exceptionally, some bright little octahedra of Cornish magnetite. Strings of magnetic iron -ore occasionally seam the rocks of the south-western counties, and declare their presence by disturbing the compass of a passing tourist. In South Devon such ore is sometimes found in quantity sufficient to invite exploration. Sir C. Le Neve Foster has described the iron-ore of Haytor, on the eastern border of Dartmoor, as occurring in the form of thick beds of magnetite, inters tratified with altered shales and sandstones of Carboniferous age.f The formation of the magne- tite by metamorphism of other ores may be connected with the intrusion of a mass of granite. The surrounding rocks are much silicified and contain hornblende, garnet, axinite and some other minerals. There are three beds of ore, with an aggregate thickness of 26 feet. In describing the bedded deposits of iron ore at Smallacombe, in Devonshire, Mr. J. H. Collins has expressed his opinion that the ore was originally a carbonate of iron which has become altered to magnetite by the action of circulating waters. } It is well known that iron ore carrying the metal as carbonate, such as spathic ore or even clay ironstone, becomes magnetic on calcination ; and it is not unlikely that magnetite may in some cases be formed from chalybite by contact with basalt or other rocks at even moderate temperature. Magnetite may likewise result from the deoxidation of haematite by means of ferrous compounds or other reducing media. Pure haematite contains 30 and magnetite 28 per cent, of oxygen ; so that the transformation does not necessitate a great amount of deoxida- tion. On the other hand, pseudomorphs of haematite after magne- tite show that the converse change may take place. Martite, which is a red oxide of iron in crystals like those of magnetite, has probably such an origin. If not a pseudomorph, Fe.,0y must be dimorphous. On the disintegration of the crystalline rocks, the magnetite which they contain tends, by its density and comparative stability, to accumulate locally in the detritus. Hence the origin of the black * " Notes on a Collection of Rooks and Fossils from Franz Josef Land." QjLirt. Journ. G&ol. Soc., vol. liii. (1897), p. 477. f " Notes on Haytor Iron-mine." Quart. Journ. Geol. Soc., vol. xxxi. (1875), p. 623. t Rzp. Mln. Aisx. Corn., 1872. HEMATITE. G7 magnetic sand found on the Cornish coast, as near Botallack. Such sands may contain also titanic iron ore or Iserine. A. similar mineral called Menaccanite takes its name from Menaccan, near Helston in Cornwall, where it was found as sand in a stream at Tregonwell Mill. Haematite (Nos. 478 to 481). Under the name of Hcematite are included all the varieties of native ferric oxide, which are either crystallised in the hexagonal system or are merely massive. The crystals have often the brilliancy of burnished steel, whence the name specular iron, iron glance or looking glass ore. This splendent lustre may be seen on the small crystals here exhibited (Nos. 478 to 480). Most of these are from Botallack Mine, and show the specular mineral implanted, as in many other localities, on quartz. In No. 479 the mineral is associated with fine bisphenoids of chalcopyrite on hexagonal prisms of quartz. The mines of Cumberland yield crystallised specimens of this mineral so much finer than anything found in the Cornish mines that fuller description of the substance may be fairly deferred until the North of England minerals are noticed (p. 144). A variety of specular haematite occurring in very fine scales is known as micaceous iron ore. Such a mineral occurs in Devonshire, near Bovey Tracey, and it is recorded that large quantities were sent to London, " in the days of pounce,"* and sold as Devonshire sand. In recent times considerable quantities have been raised in Devon- shire under the name of *' shining ore?' and exported to Germany. The specimen No. 481 shows the character of the substance. It is rather like finely divided plumbago, and may be used as a lubricat- ing agent, but it is probably employed mostly as a pigment for iron- work. It occurs in narrow lodes in granite. t Of massive haematite or red iron ore, specimens from Restor- mel may be seen in Nos. 493 to 495, which show the mineral associated with the hydra ted oxides gothite and limonite. In some cases haematite may have been derived from such hydrates by natural removal of water ; but the converse change, the hydration of red ore, is also frequent. Mr. Solly has described pseudomorphs of haematite after pyrite from Torquay. J The conversion of the sulphide into limonite is common enough, but its alteration to haematite is exceptional, and it is suggested that the haematite was there formed by the reaction of limestone on ferric chloride, due to the alteration of the pyrites by sea water. * "The Economic Geology of Devon," By R. N. Worfch. Trans. Devon Assoc., vol. vii. (1875), p. 225. De la Beche's Report on Cornwall, p. 617. f " Micaceous Iron-ore, near Boyey Tracey." By Mr. Joseph S. Martin. Trais. Maich. Geol. OC)O)>, skorodon, garlic). In No. 537 the two arsenates, pharmacosiderite and scorodite, are seated together on the gozzan of Wheal Gorland. The two minerals, though allied chemically, present marked physical differences ; for whilst the one occurs in dark green cubes the other forms pale bluish-green trans- lucent crystals, belonging to the orthorhombic system, and usually aggregated in small globular groups, with a diverging structure. Scorodite was regarded by the older mineralogists as an arsenate of copper a pardonable enough error, due to its colour and to its occurrence, with copper arsenates in the St. Day district. Cornish specimens sometimes show the scorodite on a matrix containing mis- pickel, and this association at once discloses the genesis of the mineral. Simple oxidation and hydra tion of the arsenide might readily result in the formation of scorodite. Scorodite occurs as a deposit from several of the hot springs and geysers of the Yellowstone Park, forming in some cases a brilliant green incrustation on the siliceous sinter. In this form the scorodite is a very unstable substance, readily undergoing decomposition and leaving an ochreous residue which contains more or less arsenic acid.| The rare species Liskeardite, from near Liskeard, described by Prof. N. S. Maskelyne, J is representedby a single specimen No. 541 . The mineral is a hydrated arsenate of aluminium and iron, and occurs at Marke Valley as an incrustation, associated with scorodite and mispickel two minerals which suggest its origin and relation- ship. Cronstedtite (Nos. 542 to 544). Several examples of the rare mineral Cronstedtite are here ex- hibited from Wheal Jane, near Truro, where the conditions of its occurrence, judging from the specimens, are similar to those under which the vivianite and ludlamite occur (p. 70). * Min. Mag., vol. xii. (1900), p. 152. f " Notes on the . Deposition of Scorodite from Arsenical Waters in the Yellowstone National Park." By Arnold Hague. Am. Journ. Sc., [3] vol. xxxiv. (1887), p. 171. Journ. Chem, Soc., vol. liv. (1888), p. 122. J Nature, vol. xviii. (1878), p. 426. Journ. Chem. Soc., vol xliii. (1883), p. HO. 74 MINERALS OF CORNWALL AND DEVON. Cronstedtite a mineral which borrows its name from a Swedish chemist, Axel Frederic Cronstedt (6. 1722, d. 1765) may be re- garded as a hydrous f err oso -ferric silicate. It occurs in small black lustrous crystals, referable to the hexagonal system, and remark- able for the hemimorphism which they frequently present the two extremities of the crystals having dissimilar terminations. In the specimens here shown, the mineral is mostly in radiating groups of acicular crystals, rather suggestive of schorl, but the substance is much softer. In No. 542 the little slender crystals are disposed in stellate aggregates, after the fashion of some schorl, and these repose on chalybite, which itself is spread over pyrite, at the expense of which it has evidently been formed. In No. 543 the stellate cronstedtite is associated with chalybite and a little limonite on pyrite. No. 544 shows a veinstone with copper pyrites and zinc blende ; and in a vug or cavity in this stone minerals have crystallised in the following succession (1) quartz, (2) chalybite, (3) cronstedtite.* * On the chemical and crystallographic characters of croustedtite, see " Mineralogical Notices." By Prof. N. Story-Maskelyne and Dr. Walter Flight. Journ. Chem. Soc., [2] vol. ix. (1871), p. 9. NICKEL AND COBALT-ORES. 75 CASE V. DIVISION 1. MINERALS OF CORNWALL AND DEVON. MINERALS OF THE RARER METALS. (Nos. 545 to 012.) The group of specimens exhibited in the first division of Case V. consists of minerals which contain some of the rarer metals of Corn- wall and Devon. It is true that the minerals containing silver and antimony, which might fairly take a place here, are exhibited in Case III. by side of the lead-ores, but this is an arrangement due chiefly to convenience of space, though at the same time it is an arrangement which does no violence to the natural relationship of these minerals. On the other hand, manganese, which is con- veniently represented in the case now under description, is perhaps hardly entitled to be regarded as a rare metal ; yet the ores of manganese are by no means common among Cornish minerals. An easy transition is effected from the iron-bearing minerals in the last case (No. IV.) to the rarer minerals, now to be described, through the group of nickel and cobalt ores, inasmuch as the two metals which they contain bear very close relationship to iron. Nickel and Cobalt Minerals (Nos. 545 to 548). The metals nickel and cobalt are found chiefly in the natural condition of arsenides and sulphides, but such minerals are far from common in the West of England. They occur occasionally in the copper- and tin lodes, especially the former, and also in cross-courses, usually near their intersection with the east-and-west veins. Nickel and cobalt are so closely related that they are often associated in the same ore, and the respective minerals are not always readily distinguished from each other by cursory inspection. On weather- ing, however, the arsenides give rise to arsenates, and are then readily distinguished, since the alteration-product, or " bloom," of the cobalt ore is pink, or peach-blossom tinted, whilst that of the nickel ore presents a peculiar green colour. Pentlandite (No. 545) is an iron-nickel sulphide, or nickeliferous pyrites, which was found at one time in some quantity at Wheal Jane, a lead mine near Truro. Niccolite (No. 546), often known by its old German name Kupfernickel, is a nickel arsenide, distinguished by its pale coppery red colour. It was formerly raised at the Pen- gelly Mine, in St. Ewe. CUoanthite is an arsenide of nickel with 76 MINERALS OF CORNWALL AND DEVON. cobalt, whilst smaltine, or smaltite, is an arsenide of cobalt with nickel, iron being usually present in both minerals. The specimen of smaltine (No. 547) is from Wheal Sparnon, near Redruth. Among these cobalt and nickel-bearing minerals the most attrac- tive to the eye is the Erythrite (No. 548), which is a hydrated arsenate of cobalt, resulting from the alteration of arsenical cobalt ores, on which it usually appears as an incrustation of a peach- blossom colour, deepening in some specimens into crimson. Crystals belonging to the monoclinic system, are not unknown, but most erythyrite is found as an earthy or pulverulent material, often termed cobalt-bloom. Manganese Minerals (Nos. 549 to 568). Manganese is a metal closely related to iron, and rather widely distributed in nature, though deposits of its ores are not commonly of great magnitude in the West of England. They occur chiefly in lenticular masses and irregular pockets in Devonian and Carboni- ferous strata, but not usually in persistent veins. At the Restormel Royal Iron Mine, near Lostwithiel, manganese minerals occurred in association with the iron-ores, but only in very subordinate quantity. Most of the ore-bodies containing manganese are found on the north coast of Cornwall and in the, eastern part of the county, especially near Launceston ; or in the adjacent part of Devonshire, near Tavistock, and again on the eastern side of Dart- moor, north of Exeter. One of the finest deposits was that formerly worked at Upton Pyne, where the ore was first raised about the year 1770. The same vein was also extensively worked at Newton St. Cyres, but the workings at both places were discontinued about 1810 or soon afterwards.* Manganese occurs generally in the form of an oxide, which appears to have been deposited from solution, in some cases as a direct precipitate, in others through the intermediate stage of carbonate. The original source of the metal is probably to be sought in the crystalline rocks, where it occurs in many of the constituent min- erals, like augite and hornblende, though usually in only small pro- portion. If the manganese be present as silicate, it may be readily dissolved by water containing carbonic acid, and be then held in solution as bi-carbonate. On exposure to oxidising influences, the neutral carbonate tends to pass into the state of a hydrated oxide. Manganous carbonate is, however, more stable than ferrous carbonate, and consequently in a mixture containing the two car- bonates and they often occur in association the iron will oxidise first. It has frequently been observed that in deposits containing ores of both manganese and iron, the manganese diminishes in depth while the iron increases. This is explicable on the assumption that a solution containing carbonates of both metals, rising from * De la Beche's Report on Cornwall, etc., p. 609. MANGANESE ORES. 77 below, suffered oxidation as it approached the surface. From the experiments of M. Chamussy, of the manganese mines of Rom- aneche, it appears that from an acid solution of the salts of mangan- ese and iron the effect of a base is to precipitate ferric oxide at first, and that manganese dioxide is not thrown down until long after- wards. Hence the upper part of a deposit of mixed ore is likely to be the richest in manganese.* Indeed if the oxidising influences are not very powerful, the manganese may remain as carbonate whilst the iron forms a hydrate. Manganite and other Oxides (Nos. 549 to 564). The characters of manganite, or grey oxide of manganese, are well illustrated by the specimens Nos. 549 to 562. The mineral is seen in dark steel-grey crystals, belonging to the orthorhombic system, usually in prisms with deep vertical striations. It is a hydrated sesquioxide, related in composition and crystallisation to the corre- sponding iron-mineral gothite. Pyrolusite, or black oxide of manganese (Nos. 553 to 556), is a very soft mineral, soiling the fingers, and usually occurring in compact or reniform masses, sometimes with fibrous structure. It is gener- ally a secondary mineral, resulting from the dehydration of man- ganite or from the alteration of the carbonate. When in crystals, which seem generally to be pseudomorphs after manganite, the manganese dioxide is termed polianite.^ Psilomelane is a compact black mineral, never crystallised, but usually occurring in botryoidal masses, like Nos. 557 and 560, or in stalactitic forms, as shown in Nos. 561 to 564. The surface is smooth with sub-metallic lustre, or sometimes velvety. Restormel Royal Iron Mine yielded most of the specimens exhibited herr. Psilomelane is a hydrated oxide of manganese, of variable composi- tion, frequently impure, and containing barium, etc. Manganese Carbonate and Silicate (Nos. 565 to 568). Dialogite, or native manganous carbonate, is here represented by a Cornish specimen, showing the beautiful rose-red colour which has earned for this species the name of Rhodochrosite a name now frequently employed. The crystalline structure is also well illustrated by this specimen, and from this sparry character it -is known as rose spar or manganese spar. The mineral crystallises in the rhombohedral system, and is isomorphous with calcite and chalybite. In No. 566 the dialogite appears in globular masses of a dark reddish brown colour, with a velvety surface. The colour here may be referred to the presence of iron. Another manganese mineral of pink or rose-red colour, something like the carbonate but much harder, is the silicate known as * " Traite des Gites mineraux et metalliferes." Par Ed. Fuchs et L. d3 Launay. Paris, 1893, vol. ii, p. 8. t See Laeroix's " Min^ralogie de la France" vol. Hi, 1901, pp. 235, 354. 78 MINERALS OF CORNWALL AND DEVON. Rhodonite (No. 567). The specimen here shown is from Black Down, near Tavistock, in Devonshire. The pink silicate is associ- ated with black oxide, a not infrequent occurrence, since all man- ganous compounds are prone to pass into a higher state of oxidation, with production of black oxides. In Siberia, the rhodonite is some- times cut and polished as an ornamental stone, and in this case the black alteration-products contrast strikingly with the original red mineral. No. 568 is a specimen of Penwithite, described by Mr. J. H. Collins as a hydrated silicate of manganese.* The mineral was found at Wheal Owles, in St. Just-in-Penwith, whence the specific name. The ores of manganese, chiefly pyrolusite, have considerable economic interest, being used in the production of certain alloys of iron, and in the preparation of bleaching-powder, etc. Pyrolusite is also employed as a source of oxygen, whence its value as a decolourising agent in glass-making. Bismuth minerals (Nos. 569 to 584). Minerals containing bismuth are by no means common in the West of England, but are occasionally found in tin-lodes, and especially in association with ores of cobalt and nickel. Borlase statesf that in 1755 it was found by a certain Dr. Schlosser that ores containing bismuth, with cobalt, were being thrown away at a mine in Gwennap, and he consequently devised means for saving and separating them. Native bismuth was at one time rather plentiful at Botallack. According to the late Mr. Garby, " masses of some pounds weight have been found in the soil, in the vicinity of Redruth."{ The metal crystallises in the rhombohedral system, and is often found in crystalline masses, with a platy structure, due to perfect basal cleavage. Lamellar masses of notable size have been found at the Consolidated Mines, St. Ives. The metal presents a tin- white colour, with a suspicion of red, as shown in Nos. 569 to 572. It is extremely fusible, so that miners roughly test an ore for bismuth by observing whether it fuses when placed on a heated shovel. Bismuth is one of the small group of brittle metals, including arsenic and antimony, and it is notable that the native bismuth frequently contains traces of both these metals. Native bismuth is probably a mineral of secondary origin ; and it has been suggested by von Fritsch that it may in some cases have been deposited from solutions by electrolytic action.il * Min. Mag., vol. ii. (1879), p. 91 ; vol. iii. (1880), p. 89. \ " The Natural History of Cornwall." By William Borlase, Oxford, 1758, p. 131. Trews. R. Geol. Soc. Corn., vol. vii. (1865), p. 86. Collins's " Mineralogy of Cornwall," p. 16. || " Ueber die Mitwirkung elektrischer Strome bei der Bildung einiger Mineralien." K. von Fritsche. Dissert. Gottingen, 1862. PITCHBLENDE. 79 The trisulphide of bismuth occurs native, forming the mineral known as Bismuth glance, or bismuthite or bismuthinite (Nos. 573 to 581). Like stibnite, to which it is chemically related, it crystal- lises in the orthorhombic system, and is usually found in acicular crystals. These needles, well seen in most of the specimens exhibited here, have a tin -white or lead-grey colour, with metallic lustre ; but the surface is often obscured by a tarnish, sometimes slightly iridescent. In some specimens, the mineral assumes a filamentous or capillary form, and some beautifully delicate tufts of brown fibres are seen in Nos. 578 and 579. In No. 578 these hair-like crystals are associated with cubes of almost colourless fluor-spar. The association with this spar is also seen in No. 581. It is probable that the sulphide represents the original form in which the bismuth was introduced into the vein ; and the frequent presence of fluorite as a companion suggests that fluorine may have been active at the same time. Bismite, or bismuth ochre, is a yellow or brown earthy oxide, result- ing from the alteration of native bismuth and bismuth glance, as seen on specimens Nos. 582 to 584. Pitchblende (Nos. 585 to 587). Occurring usually as a black massive substance, without any strik- ing individuality, this mineral was mistaken by the early mineral- ogists for other substances, such as certain ores of zinc and iron. Its pitch-like appearance and its deceptive characters led to the trivial name of pitchblende a name which still clings to the mineral, even in scientific writings. In 1789 Klaproth showed that pitchblende contained a distinctive metal, previously unrecognised ; and as Herschel had just then discovered the planet Uranus, the new metal was rather fancifully named Uranium. From the presence of this metal, the pitchblende was called by Haidinger Uranin a word which was modified by J. D. Dana as uraninite. Uraninite, or pitchblende, was formerly regarded as an impure oxide of uranium, and it does indeed contain a large proportion, exceeding in some cases 80 per cent., of U 5 8 . This may be present as uranous and uranic oxides (respectively containing U0 2 and U0 8 ), whence the mineral was considered at one time to be a proto-peroxide of uranium. It is sometimes described as a uranate of uranyl. JVfodern research, however, has shown that it is a substance of great complexity, containing lead, bismuth, barium and various rare elements. Most varieties of pitchblende contain thorium or zirconium, and certain metals of the lanthanum and yttrium groups. The chemical composition of uraninite has been elaborately investigated by Dr. Hillebrand, of the Geological Survey of the United States. In the course of his analysis he obtained, by boiling the mineral with weak sulphuric acid, a gas which was regarded as nitrogen.* After the discovery of argon by Lord Rayleigh and Sir * " On the occurrence of nitrogen in Uraninite." Butt. U.S. Geolog. Surv. No. 78, 1889. 80 MINERALS OF CORNWALL ANT) DEVON. W. Ramsay, it was suggested by Prof. Miers that the pitchblende gas should be examined. This examination led Ramsay to the discovery of terrestrial helium. He found that the gas evolved from cleveite, a Norwegian variety of pitchblende, when examined spectroscopic- ally, yielded a characteristic line which had been observed in the solar chromosphere by Sir Norman Lockyer as far back as 1868, and referred to a hypothetical element provisionally termed helium.* The Cornish pitchblende yields only a very small amount of this gaseous body. Great interest has attached to pitchblende in recent years by reason of it> remarkable radio-activity. The property of emitting what are called Becquerel rays was known to be possessed by the metals uranium and thorium, but the investigations of Madame Curie, of Paris, showed that pitchblende was more active than either of these metals. In order to explain this unexpected behaviour she assumed that the mineral must contain some other element of intense radio-activity an assumption which was confirmed, after a long course of laborious and delicate research, by the discovery of Radium. It is interesting to note that the three elements which have the highest atomic weights are the three radio-active bodies which occur associated, with others, in pitchblende, namely : Uranium, atomic weightf - - ... 238.5 Thorium, - 232.5 Radium, - 225 Evidence has been obtained by M. and Mme. Curie, working with M. Bemont, of the existence of another substance of high radio- activity, described as a new ' element ' under the name of polonium ; whilst a third new element has been announced by M. Debierne under the name of actinium. In preparing compounds of these bodies from pitchblende, it is found that the radium associates itself with barium, the polonium with bismuth, and the actinium with the rare earths. Yet another substance of great radio-activity has been obtained from pitchblende by M. Marckwald, who has described it as radio-tellurium ; but it is suggested that this may be a form of polonium. None of these newly-discovered substances occurs in pitchblende in more than infinitesimal proportion. Of radium, which is the best known and probably the most abundant, it is estimated that only about three grains are contained in a ton of the richest pitchblende. The occurrence of pitchblende has been recorded from a number of Cornish localities, but it is rarely found in large quantity. Dr. Richard Pearce, in describing its discovery some years ago at Wheal * " On a gas showing the spectrum of Helium." By William Ramsay. Proc. Roy. Soc., vol. Iviii. (1895), p. 65 ; also p. 81, and vol. lix., p. 325. '" On the new gas obtained from Uraninite." By J. Norman Lockyer, C.B. Ibid., vol. Iviii., p. 67 ; also pp. 113, 116, 192, 193 ; and vol. lix., p. 342. f International Atomic Weights (0 = 16.) Journ. Chem. Soc., vol. Ixxlxii. (1902.) URANIUM-ORES. 81 Owles, in St. Just, pointed out that the Cornish pitchblende usually occurs in association with other rare minerals at St. Austell Consols with nickel- and cobalt- ores ; at Dolcoath with native bismuth and arsenical cobalt ; at South Tresavean with kupfernickel, native silver and rich argentiferous gozzan. The uranium minerals seem to occur mostly in small cross-veins.* In recent years uranium- ores have been successfully worked at Grampound Road, in the parish of St. Stephens, in West Cornwall at a mine formerly worked for tin, under the name of South Terras. An abundant development of gozzan near the surface yielded a mixture of earthy minerals, variable in composition, containing uranium chiefly in the form of cupro-uranite and calco-uranite. These ores gave way below the 10-fathom level to pitchblende the mineral from which they had evidently been derived. The pitch- blende occurred in a quartz veinstone, associated with much oxide of iron and with occasional bunches of copper ore and argentiferous galena. According to Mr. B. Kitto the uranium ores occurred in a vein about three feet wide, coursing through killas in a north and south direction. The ores were formerly treated by him, and converted into ' orange ' and ' yellow oxide,' most of which was sent to Germany. Uranium compounds are used in porcelain painting, in photography, and in the manufacture of the greenish yellow uranium glass, well known for its fluorescence. It has also been proposed to employ uranium in steel manufacture. In 1901 the mines at Grampound produced seventy-nine tons of uranium ore, valued at the mine at 2,923.f The mines have since been closed, but will probably be re-opened with the view of supplying material as a source of radium. The uranium mines have been recently visited by Mr. Clement Reid, in the course of his official work on the Geological Survey. It appears that there are at least two parallel veins, representing cross-courses ; and the ore is found to be associated with much magnetite and garnet. Mr. Reid has observed that these veins carry a green garnet, which seems to be grossularia a mineral which it is believed has not been previously recorded from Cornwall . No. 588 is a specimen of Zippeite from Wheal Edward, St. Just. Evidently resulting from the direct or indirect alteration of pitch- blende, it appears as a delicate canary-yellow incrustation, with a fibre-scaly structure. With other products of the decomposition of uranium ores, both oxides and sulphates, the zippeite is some- times known as uranium-ochre. Uranite (Nos. 589 to 608). Two minerals have been included under the general name of Uranite. Both contain hydrated phosphate of uranium, but in the Note on Pitchblende in Cornwall." By Richard Pearce. Trans. Roy. Soc. Corn., vol. ix., p. 103. Mineral Statistics." Home Office Report for 1901 (1902), p. 271. 882. G 82 MINERALS OP CORNWALL AND DEVON. one case the uranium is associated with copper, in the other with calcium. Hence two species are recognised, known respectively as Cupro-uranite, or copper-uranite, and Calco-uranite, oilime-uranite. The former is a green mineral, the latter yellow. Although they eoem to agree in the character of their crystallisation, the copper- hearing mineral belongs to the tetragonal system, whilst the lime species is now known to be orthorhombic. Cornwall is famous for its fine specimens of cupro-uranite, of which many beautiful examples are here exhibited (Nos. 589 to 604). The vivid green colour, the brilliant lustre, the characteristic habit of the crystals and their associations are fully illustrated. The mineral ' is generally in thin plates, square or octagonal, sometimes curved, and always very fragile ; whilst occasionally it appears in rather stout, square, tabular crystals, bearing pyramidal faces at the edges, and exhibiting a perfect basal cleavage. This cleavage is apt to impart a micaceous structure to the mineral, whence it was formerly known as uranium mica. As far back as 1815 the Cornish uranite was examined by William Phillips, who figured a large series of crystals.* At that time the mineral was regarded as an oxide of uranium. Many of the fine old Cornish specimens were obtained from the copper-mine of Gunnislike, near Callington, where they occurred in gozzan at as great a depth as 90 fathoms from the surface. Nos. 589 and 590 show the curved platy crystalline masses from this locality, whilst No. 597, also from Gunnislake, shows them spread out in plumose form on a veinstone of quartz with oxide of iron associated with oxide of manganese. In other specimens, such as Nos. 601 and 602, the crystals are seated on a brown cavernous matrix of gossan. Uranite appears in some cases to be connected with the kaolinisation of felspar ; and in Nos. 594 and 595, from near Redruth, the uranium mineral is seen on altered granite, the brilliant emerald-green crystals forming a striking contrast with the dead white matrix. At Stenna Gwynn the mineral is associated with fluellite. According to Mr. J. H. Collins, uranite is so widely distributed m Cornwall that it occurs " in the shallow parts of almost every copper-mine in the county. "f In connection with the self-lumin- osity of radio-active bodies, it may be worth recalling the observa- tion of the late Mr. Garby that the specimens of uranite " when first discovered by the miners in Huel Buller and Huel Basset were very phosphorescent so much so that after the lights were ex- tinguished many of the crystals might be discovered in situ."l The observations of Madame Curie have shown, as might be expected, that both the copper- and the lime- uranites are radio - * " On the Oxyd of Uranium, the production of Cornwall, together with a description and series of its Crystalline forms." Trans. Oeol. Soc., vol. iii., p. 112. f Journ. Roy. Inst. Cornwall, vol. xii. (1895), p. 52. j Trans. Roy. Geolog. Soc., Corn., vol. vii. (1865), p. 86. UEANITE AND CHtJRCHITJE. 83 active ; and though not so active generally as most pitchblendes they are yet more powerful than metallic uranium.* Torberite, a name by which cupro-uranite is sometimes known, was given to the mineral by Werner, in honour of the Swedish chemist, Torber Bergmann. As his Christian name was latinised as Torbernus, the mineral name is preferably written Torbernite.f Chalcolite is another name given to the mineral, but it is apt to be confused with Chalcocite, a name frequently applied to copper glance. The lime-uranite, known also from a French locality as Autunite, is less common than the copper-uranite, and usually occurs in yellow or pale yellowish-green crystals, as seen in specimens Nos. 605 to 608. No. 605 shows the intimate association of torbernite and autunite. Some of the Cornish autunite has been analysed by Prof. Church.* It has been suggested by M. Bourgeois that if water charged with sulphuric acid from decomposing pyrites should flow over pitch- blende with copper phosphates or with apatite, it rnight give rise in the former case to torbernite, and in the latter to autunite a view supported by the synthetic researches of Debray and Winkler, which show the possibility of the required reactions. Churchite (Nos. 609 to 612). In 1865 Prof. A. H. Church announced the discovery of cerium for the first time in this country. He found it in a mineral investing quartz and killas, from a Cornish copper lode.|| The mineral jiroved to be essentially a hydrous phosphate of cerium ; and Mr. Greville Williams, who called attention to the presence of didy- mium, as indicated by means of the spectroscope, suggested that the mineral should be named after its discoverer Churchite.^ No. 612 is interesting as being part of the original specimen analysed by Prof. Church, by whom it was presented to the Museum. The presence of cerium has since been detected by Church in several Cornish apatites. * " Radio-active Substances," a Translation of Madame Curie's Thesis. Chem. News, vol. Ixxxviii. (1903), p. 99. f " On Mineralogical Nomenclature.'- By J. D. Dana. Am. Journ. Sc. [2], vol. xliv. (1867), p. 147. t " On the Composition of Autunite." Journ. Chem. Soc. [2], vol. xiii. (1875), p. 109. Bull. Min. Soc. Fr., vol. xxi. (1898), p. 32. || " Preliminary Note on a new British Mineral, containing cerium." Chem News, 15th Sept., 18(55, p. 121. Also Journ. Chem. Soc. [2], vol. iii. (1865), p. 259. If " On the presence of Didymium in Churchite/' Chem. News, 20th Oct., 1865, p. 183. 7882. G 2 84 MINERALS OF CORNWALL AND DEVON. DIVISION 2. MINERALS OF CORNWALL AND DEVON. THE SPARS OF THE MINERAL VEINS. (Nos. 613 to 690). All the crystalline minerals which occur in veins, -but contain either no metal or only some of the rarer and lighter metals, and which never present a metallic aspect, are conveniently, though rather loosely, grouped together under the popular name of " spars." It is true that the rhombohedral carbonates, which are typical spars, may contain some of the heavy metals and may even be used as ores, so that we speak of the sparry ores of iron, manganese and zinc. But apart from these carbonates, the term is restricted to such minerals as accompany the ores in the form of matrix, gangue, veinstone or lode-stuff, and which are generally regarded as non- metallic or earthy and almost useless.* Useless as they may be to the miner, they are of the first import- ance to the student of mineralogy, inasmuch as they frequently crystallise in forms of much beauty and great scientific interest, whilst their study tends in many cases to throw light on the nature and origin of vein-formations The principal sparry minerals in the mines of Cornwall and Devon are quartz and fluorspar, with calcite and barytes in subordinate quantity. In some cases these sparry minerals form small veins, or strings, unaccompanied by any metalliferous mineral, but in most cases they occur in association with more or less ore, the association being often so intimate as to lead to the inference that both matrix and ore must have been introduced into the vein under similar conditions. It is evident that in many cases the mineral matter has been deposited in the cracks of the rocks from a state of solution. Such fissures may be due partly perhaps to the contraction of eruptive rocks on cooling or of sedimentary rocks on consolidation, partly to disruption consequent on the intrusion of igneous matter, or in con- nection with wider earth movements which have affected large areas of the earth's crust. Mineral veins often run along fault planes. Whatever the origin of these rock fissures, they would form easy channels through which waters could circulate, bringing with them mineral matter in a state of solution. Solution is usually, though not in variably, facilitated by increase of temperature and of pressure, so that solvents will generally be more effective at great depths than near the surface. A solution, as it travels upwards, along the natural conduit, will be gradually reduced in temperature and relieved of pressure, so that it will become less competent to carry its freight * Against the use of the word " gangue " see Sir C. Le Neve Foster's remarks in his " Ore and Stone Mining," p. 1 1. The term " veinstone " is rather ambiguous, since itis employed by some writers to denote the whole contents of the vein, both matrix and ore ; whilst others restrict it to the gangue- minerals, or ' waste." FLUORITE. 85 of dissolved mineral matter, some of which may consequently be precipitated on the walls of the fissure. The circulating water may have come originally from surface-drainage, and if so will be simply on its return-path, but it is returning charged with more or less mineral matter which it has dissolved during its subterranean sojourn. Solution is more active below, precipitation more active above. There is not unreasonably a tendency to regard the warm springs, which are sometimes cut in a mine, as surviving representatives of such activities as may have been potent in the deposition of the mineral contents of a vein. It is true that Mr. Kenwood remarked that some of the warmest streams he had examined had been from very unproductive lodes. But this obviously does not exclude thermal waters from having been instrumental in depositing the non-metallic veinstuff , or even metallic minerals at former geological periods. Siliceous deposits containing to a limited extent certain metallic sulphides, and therefore representing true mineral veins, have been observed in course of formation from thermal waters at Steamboat Springs, Nevada ; at Sulphur Bank, California ; and at Boulder Hot Springs, Montana.* The minerals deposited from solution may be either compact or crystalline in texture ; and if the solution should stagnate in a sub- terranean cavity the dissolved matter may very slowly be precipi- tated, and thus form distinct crystals. Large and fine crystals are generally deposited with extreme slowness. Most of the beautiful crystals exhibited in this collection have been obtained from the walls of fissures, or cavities called vugs in the veinstone, where the conditions must have been exceptionally favourable for crystallisa- tion. A vein-fissure representing a plane of weakness in the rock may have opened again and again ; and, offering each time a ready conduit for the circulation of mineral solutions, may have received successive deposits in the course of the history of the lode. The second division of Case V. is devoted to a fine series of speci- mens of fluorspar, whilst the other principal spars quartz, calcite and barytes are grouped together in the first division of Case VI. Fluorite (Nos. 613 to 690). Since it is believed that the Cornish tinstone has been formed from a tin fluoride, it might reasonably be supposed that fluorspar, the commonest of all natural compounds of fluorine, would be frequently found in tin-lodes. Examples of the association of cassiterite and fluorite are shown in Case I. and have been noticed at p. 26. As a matter of fact, however, the Cornish tin-ore is not so commonly * See J. Arthur Phillips, Phil. Mag., vol. xxxvi. (1868), p. 321 ; and '' Ore Deposits," 2nd ed., p. 115. The Boulder Springs have been described by Mr. W. H. Weed. 86 MINERALS OF CORNWALL AND DEVONT. accompanied by fluorite, at any rate macroscopically, as might be assumed. This paucity of fluor, which is a calcium fluoride, may be connected with the general scarcity of calcareous matter in the tin districts of Western Cornwall. In the copper-lodes, however, and yet more notably in the lead-veins, fluorspar is common. This is especially marked in the lead district near Liskeard, where calcite is also a characteristic mineral. Many of the fine specimens of fluorite in this collection are from the lead-lodes of Eastern Cornwall and Western Devon. The mineral known as Fluorite, fluorspar, or simply fluor, and often termed by Cornish miners cann, is a fluoride of calcium, crystallising in the cubic or regular system. Sharply defined cubes, often of large size, are very common : witness such examples as Nos. 613, 618, 622, 678, and 681. A little to the left of this collection stands a Pedestal Case, opposite Wall Case 18, which contains some cubic crystals of fluorite, each measuring more than a foot along the edge. In this specimen, from Wheal Mary Ann at Menheniot, the cubes are of deep blue colour, and certain faces are partially coated with a deposit of pyrites. It is notable that these gigantic cubes are built up of an aggregation of smaller cubes, or sub -individuals. Octahedral crystals are rare in British fluors. No. 648 shows a combination of the octahedron and cube, whilst No. 668, from Beer Alston in Devon, has the general form of an octahedron, but is a polysynthetic structure made up of aggregated cubes. Yet whatever the external shape of the crystal, fluorite always presents a perfect cleavage parallel to planes of the regular octahedron. The direction of cleavage is so marked in No. 621, that although the cubic crystals maintain their integrity, it is evident that a very slight shock would detach from each three-faced solid angle, or quoin, a tetrahedron which would leave an equilateral triangle representing the face of an octahedron. In like manner the octa- hedral planes of cleavage are visible in the cracks which run across the translucent quoins of the huge blue cubes in the adjacent case opposite Wall Case 18. The four-faced cube, known technically as the tetrakis-hexa- hedron, a kind of cube which seems to carry upon each of its faces a four-sided pyramid, is so characteristic of fluorite that it has been called the fluoroid. Sometimes it occurs alone, as in the little violet crystals on No 647, but usually it is found in combination with the cube. Thus, in Nos. 638, 649, 650, 651, not to mention others, the twelve edges of the cube are in each specimen bevelled by the planes of the four-faced cube. Most of these specimens come from St. Agnes, and it is notable that the faces of the tetrakis- hexahedron are, in some cases, rough and corroded whilst the faces of the cube remain brilliant. It often happens that the faces of a cube of fluor, instead of being quite plane, show markings which represent a very low square pyra- mid, as may be distinctly seen on No. 621. These facets are known as vicinal faces, and possess much significance to the crystallo- grapher. l - FLUORITE. . 87 Another form not infrequently found on crystals of Cornish fluorite is the six-faced octahedron, or hexakis-octahedron. The faces of this form replace the solid angles of the cube, as is clearly shown in the fine specimens of yellow and blue fluor from Wheal Mary Ann, Menheniot, such as Nos. 615, 622, and 623. Thus, in No. 622, which is part of a large cube of blue fluor, the three-faced solid angle is replaced by six planes, which if repeated on all the cube-quoins would constitute the perfect forty-eight-sided form. It will be noted that these corner faces are rough, and this led to the suggestion when such crystals were discovered many years ago, near Liskeard, that the triangular faces might have been artificially filed, but it became evident, on close examination, that the modifica- tion was perfectly natural. Other forms are not common on Cornish fluor, but occasionally the rhombic dodecahedron is represented. On No. 654 the edges of the cube are truncated by rough, rather rounded, inconspicuous planes of this solid. Peculiar interest attaches to this specimen, inasmuch as it shows an internal cube which has been coated with pyrites, upon which more fluor has been deposited, and through this transparent envelope the brilliant brassy pyrite is clearly visible. Stages in the growth of a crystal may often be detected in fluor- spar, and many of the specimens, such as Nos. 622, 631, 632, and 633, show a zonal structure, due to a regular sequence of deposits. Bands of colour often mark successive episodes in the history of a crystal. Such colour-bands may be detected in many of these specimens ; No. 633, for example, is a polished slab which shows, with exceptional distinctness, a number of parallel stripes of vivid green colour. The purple fluors, numbered 631 and 632, are also remarkable for their colour-bands. In Nos. 622 and 623, deep blue zones are well seen in the interior of pale blue cubes. Fluorite is a mineral which displays great diversity of colour, as seen in the specimens in this Case ; but even a greater variety is seen in the Ludlam Collection in the Hall, where Case III. is en- tirely given up to this polychromatic species. As this series includes foreign specimens, it contains some which possess tints unknown among our British fluors, such, for instance, as the beautiful pink fluor-spar from Switzerland. Fluor destitute of colour is quite a rarity. No. 616, from Beei Alston, approaches the colourless condition. The dispersive power and refractive power of fluor render the pellucid colourless mineral of value for the construction of objectives for microscopes, as intro- duced by Prof. Abbe. A variety from Switzerland has been applied to this purpose. The lenses of fluor are used in conjunction with lenses of Jena glass, so as to produce an improved kind of achro- matic objective which is termed ' apochromatic.'^ * See Prof. Miers's " Mineralogy," 1902, p. 96. t"Jena Glass. 1 ' By Dr. H. Hovestadt. Translated and edited by J. D. Everett, M.A., F.R.S., and Alice Everett, M.A. 1902. P. 88. 88 MINERALS Ol CORNWALL AND DEVON. Many of the specimens exhibited in this Case show that the faces of crystals of fluor-spar are apt to be corroded and etched to a re- markable extent. Nos. 616, 618, 620, and 656, not to cite other instances, clearly show the etched figures due to the action of natural solvents. In some of the specimens from Beer Alston the edges and solid angles have been so roughened and rounded that the cubes show a tendency to become rather spherical, as seen in Nos. 660, 661. From the old mines of Beer Alston, between Tavistock and Plymouth, where argentiferous galena was formerly worked on an extensive scale, a fine suite of crystallized fluors is here exhibited, including certain specimens of rich smalt-blue colour, and others of pale sea-green tints, such as Nos. 657 to 668. It is notable that while the lead mines of South Devon have yielded such fine specimens of fluor, the old mines of silver-lead in North Devon, like Combe Martin, were not remarkable for this mineral. Some of the boldest crystals of fluorite shown in this case were obtained from the lead mines formerly worked at Menheniot near Liskeard, especially from Wheal Mary Ann. Many of these show characteristic associations of minerals. Thus in No. 653 the fine yellow cubes, implanted on crystalline quartz, are sprinkled over with brilliant cubo-octahedra of pyrite. No. 669 is an instructive specimen, showing large octahedra of pale green fluor coated with minutely crystallized quartz, giving a white druey surface to the crystals, and on this surface there has been formed a second deposit of fluor, this time in purple crystals, showing a combination of cube and four-faced cube, and finally on this purple fluor copper-pyrites has crystallized. In No. 674, from near Redruth, a base of copper-pyrites having a tarnished surface, due probably to a coating of covellite, carries prismatic crystals of dead white quartz, associated with fluorite in pale yellowish green cubes, having the quoins modified by planes of the six-faced octahedron and the interior zoned with blue bands. In No. 675, from Caradon, a matrix of green fluor is partly hidden beneath a crop of snow white crystals of quartz, on which occurs a second growth of green fluorite, bearing a final crystallization of copper-pyrites. Calcite is associated with several of the specimens of fluorite from Menheniot. Thus, the blue cubes of fluor in No. 670 are moulded on crystals of quartz, but carry on their surface calcite in white crystals, consisting of obtuse rhombohedra combined with the hexa- gonal prism. In No. 681, again, fine cubes of blue fluor are encrusted on certain faces with quartz in small crystals, producing a drusy surface, and on this quartz calcite has finally crystallized. It is notable that fluorite is often pyrophosphoric, that is to say, it becomes self-luminous on exposure to very moderate heat. The amorphous opaque white fluor, No. 686, is remarkable for its phos- phorescence. When slightly heated it emits a beautiful green glow, whence the name Chlorophane sometimes applied to such a variety of fluor whence also the term pyro-emerald. Since this white fluor FLUORITE. 89 exhibits a green light, the colour of the phosphorescent glow seems to bear no necessary relation to the colour of the mineral. Pseudomorphs after fluorite are well known to collectors. In Nos. 687 and 688 cubes of fluor are encrusted with a deposit of quartz, giving the crystals a drusy surface. In No. 689 the fluor has been removed by solution, leaving a cubic hollow, in which a little chaly- bite has crystallized. Other epimorphs, showing cube-shaped cavities, left probably by the removal of fluor-spar, are exhibited in Case IV. (see No. 515, p. 69). In No. 690 from Tavistock, octahedra of pale green fluorite are superficially replaced by opaque white chalcedonic silica, or horn- stone. In Case VI., the specimen No. 774 shows a fine octahedron, consisting of chalcedony which has entirely taken the place of fluorite. The ultimate source of much of the fluorite in the Cornish lodes is probably to be traced back to a very early phase in the history of the veins. Some of the fluor may indeed have been connected with the original formation of the tinstone. If it be admitted that the cassiterite has been formed by the reaction of tin-fluoride and water- vapour, it is evident that the formation of the stannic oxide would be accompanied by the production of hydrofluoric acid. This acid acting on lime-bearing minerals, such as certain felspathic constituents of the granite, might produce calcium fluoride. Hence the forma- tion of cassiterite would be accompanied or followed by the produc- tion of fluor-spar. It is known that fluorine, in the form of hydrofluoric acid and fluoride of silicon, occurs among the exhalations from fumaroles, whilst calcium fluoride and other solid substances containing fluorine are found among volcanic sublimates. There is no reason to doubt, however, that most of the fluorite from the mines of Corn- wall and Devon has been formed by deposition from solution, pro- bably in thermal waters. Fluorine is known to occur in certain natural waters, notably in some of the hot springs of Galicia. Whilst it is present in some waters as sodium fluoride, it exists in others as calcium fluoride. Small crystals of fluor have been found on mortar in the old Roman baths of Plombieres ; but here it was probably derived from the fluorite which existed in the granite through which the water passed. Glasses used at thermal springs often acquire a dull surface, but the popular notion that this is due to corrosion by hydrofluoric acid is not always correct. 90 MINERALS OF CORNWALL AND DEVON. CASE VI, DIVISION 1, MINERALS OF CORNWALL AND DEVON. THE SPARS OF THE MINERAL VEINS, CONTINUED. Quartz (Nos. 691 to 718). Of all the minerals which contribute to the formation of the vein- stones in the West of England, Quartz is by far the most abundant. * As it is so much harder than the other sparry minerals of the veins fluorite, calcite and barytes all yielding readily to the knife whilst quartz resists it is sometimes termed by the miners ' hard spar ' ; or it is referred to, in consequence of its abundance, as simply ' spar.' Some of its general characters have already been noticed (p. 21). Where cavities, or vugs, occur in the veinstone, the quartz will have opportunity for free crystallisation, and the walls of these hollows may consequently be lined with crystals. In like manner, the sides of fissures in granitic or slaty rocks, may be studded with crystals of quartz. It is from such situations that the fine speci- mens here exhibited have been derived. A crystal of quartz, when developed under favourable conditions, usually assumes the form of a six-sided prism, attached by its base to the veinstone or to the mother-rock, and terminated at the free end by a six-sided pyramid. Most of the crystals in this case exhibit such a combination of forms. In many of the specimens the prisms are elongated along the vertical axis, producing slender crystals, whilst in others the planes of the terminal pyramid pre- dominate, giving rise to groups of short sharp-pointed crystals : Nos. 695 and 696 illustrate the former, and No. 691 the latter habit. In the quartz-porphyry of many Cornish elvans bi-pyramids of quartz are not uncommon. In No. 693 the crystal of quartz appears to be flattened by the development of two opposite faces of the prisms at the expense of the others. The planes of the terminal pyramid may be equally developed, producing regular forms like those of No. 070 ; but it frequently happens that the pyramidal planes are alternately large and small, as seen in No. 096, thus suggesting that the faces are really those of two correlative rhombo- hedra. It is very characteristic of quartz that the prism faces are striated transversely, that is, in a direction perpendicular to the morpho- logical axis, as seen with great distinctness in Nos. 694 and 696. This is due to an oscillatory combination of the prism and a pyramid. * Quartz is probably the most widely distributed mineral in Nature " next to water." (Max Bauer's Lehrbuch der Mineralogie, Stuttgart : 1904.) QUARTZ. 91 Most of the crystals of quartz in the series, numbered 691 to 698, are more or less opaque, in some cases snow-white or dead- white. This character is common in crystals of quartz from veinstones, whereas quartz which crystallises in the fissures of granite and slate is often transparent, and sometimes quite pellucid. When clear and colourless quartz is known as Rock crystal, and crystals of this kind may be found in nests along the joints of slaty rocks in the cliffs at Tintagel and in the Delabole quarries. Small crystals are usually more perfect in shape and brilliant in lustre than large ones. The limpid colourless crystals are known as Cornish diamonds. In describing the old museum of the Royal Society, Grew wrote : " Of our bastard diamonds here in England the Cornish are the best."* Borlase, in his " History," describes and figures a number of Cornish crystals of quartz, referring especially to a very fine collection made by Mrs. Grace Percival, and preserved " in her Fossilary " at Pendarves for the " attentive inspection of every inquisitive Fossilist."f Quartz sometimes assumes a brown colour, more or less pro- nounced, and is then termed Smoky quartz. No. 707 is a beautifully sharp and clear crystal, from Tintagel, with a faint brown tinge. The colour of smoky quartz is often referred to the presence of organic matter, but in some cases it is said by Weinschenk to be due to the presence of a compound of titanium. This crystal en- closes delicate hair-brown needles, probably of rutile, or titanium dioxide. In the fine example of capped quartz, No. 700, a hexagonal pyra- mid of the mineral fits perfectly into a hollow envelope, which has formed its cap. Between the formation of the crystal and the cap, a thin coating of some foreign substance, like mica in some specimens or clay in others, has been deposited, so as to interrupt the continuity of growth and secure freedom between the original formation and its shell. No. 701 shows a curious form of yellowish quartz in globular masses composed of diverging columnar crystals, which give rise, on fracture, to a stellate appearance. Since fibrous quartz is occasionally found in the cross -courses in Cornwall, it is known to the miners as cross-course spar. The so-called hacked quartz, represented by No. 703, is crystalline quartz with apparent incisions, as though the mineral had been cut. These hollows have been left by the disappearance of thin tabular crystals, probably barytes, between which the quartz had been deposited. In No. 704 from Herodsfoot Mine the crystallised quartz forms an epimorph, having invested tabular barytes, which on removal would leave imprints like those of hacked quartz. The well-known Babel quartz is illustrated by No. 705, from Beer- alston in Devonshire. Here the white crystalline quartz has been * "Museum Regalis Societatis," London: 1681, p. 283. t " The Natural History of Cornwall," Oxford : 1758, p. 122. 92 MINERALS OF CORNWALL AND DEVON. developed in little step-faced turrets, rising from a broadly extended face of quartz, which seems to have been itself deposited on crystals of fluor-spar, now vanished. Amethyst, more or less pronounced in colour, is occasionally found in the mineral-veins of Cornwall, and notable specimens have been obtained from Wheal Uny and Wheal Tolgus, near Kedruth. In No. 708 the violet tint is pale, whilst in No. 709 it is a rich deep colour, and in No. 710 the pigment seems so dense as to render the crystal practically black. The colour of amethyst is commonly referred to the presence of manganese, in the state of oxide. It is notable that on exposure to a moderate heat the amethystine colour is lost, and the mineral becomes greenish yellow, like the variety of quartz known as Citrine. Much of the yellow quartz used as an ornamental stone is simply " burnt amethyst." Veins of amethys- tine quartz lose their colour at the outcrop, becoming first greenish and then colourless. Sulphur has been detected in certain kinds of amethyst, and the colouring agent has been regarded by A. Nabl as ferric thiocyanate.* Professor Judd has shown that amethyst usually exhibits a lamellar structure, due to mechanical stresses, and has suggested that quartz which has a tendency to undergo this molecular change should be distinguished as unstable quartz. f Such quartz presents, on fracture, a rippled surface ; and all quartz which displays this structure, whatever its colour, is sometimes termed, following Brewster, amethyst. The intersection of two systems of curved ripples or ' thumb-mark",' may produce on the fractured face a pattern not unlike that resulting from ' engine turning.' The un- stable quartz has a great tendency to assume purple colours, and, moreover, the colour is often concentrated along the lines between the lamella?. The optical properties of amethyst have been the subject of much study ; and it is notable that the component lamellae in the mineral are alternately right-handed and left-handed with regard to their action on polarised light. Red quartz, known frequently as Eisenkiesel, owes its colour in most cases to mechanically enclosed oxide of iron. Such iron quartz is well illustrated by the series Nos. 711 to 714, from the Restormel Royal Iron Mine, near Lostwithiel. In No. 713 the rich red quartz is associated with psilomelane, or oxide of manganese. Quartz crystals not infrequently enclose foreign substances, such as the specular iron-ore in No. 694. The interesting specimen No. 715, from Cook's Kitchen, near Camborne, shows large crystals of quartz bearing hollow epimorphs, which are thin crusts that have taken the form of lenticular crystals of chalybite and are themselves sprinkled over with red oxide of iron. * Journ. Chem. Soc., 1899 (Abstracts), p. 561. f " On the Development of a Lamellar Structure in Quartz -crystals by mechanical means." By Prof. John W. Judd, F.R.S. Min. Mag., ^ol. viii. (1889), p. 1. Also : " Additional Notes." Ibid, vol x. (1894), p. 123. CALCITE. 03 No. 716, from Botallack, is a specimen of quartz pseudomorphous after calcite in obtuse rhombohedra. Many interesting associations of quartz will be observed in this series. Some very fine bisphenoids of copper-pyrites are crystallised on the group of prismatic crystals of quartz in No. 696, from Red- ruth, whence also was obtained the next specimen (697) which shows a somewhat similar grouping of quartz and chalcopyrite. Excellent crystals of mispickel have seated themselves on the quartz in No. 695. The history recorded by the specimen, No. 698 is as follows : opaque white quartz has crystallised on a chloritic veinstone, with copper pyrites ; then chalcopyrite in bisphenoids, now tarnished, has been formed on the quartz ; and finally, chalybite has been developed, in aggregates of fish-scale crystals. In No. 691 sea-green fluorspar has crystallised in bold cubes on quartz in fine hexagonal prisms, with pyramidal terminations ; and then a secondary growth of quartz has taken place, this time in small crystals beautifully pellucid, and doubly terminated. In many other specimens it will be noticed that a second crop of quartz crystals, often of small size, has been formed on large pre-existing crystals of quartz. Calcite (Nos. 719 to 742). Carbonate of lime is rare in the veinstones of Cornwall, and is practically absent where the veins run through granite. In eastern Cornwall there is more calcareous matter than in the west, and Mr. Collins has suggested that this " perhaps points to a former westward extension of overlying Devonian limestones."* In the tin lodes of the west, carbonate of lime is quite an exceptional mineral. The specimen, No. 38 (Case I.), is interesting as showing wood- tin with the laminated variety of calcite known as S chief er spar or " slate spar." Most of the specimens in this Case have been obtained from the lead mines near Liskeard, especially from Herods- foot and Wheal Wrey. Calcite, or native carbonate of lime, crystallises in the hexagonal system, and presents perfect cleavage parallel to the fundamental rhombohedron. Greg and Lettsom remark that " in Cornwall and Devonshire low hexagonal prisms and tabular forms prevail." f This assertion is partly justified by No. 739 from Botallack, and No. 740 from Wheal Friendship, near Tavistock the crystals in both specimens having a tabular habit by predominance of the basal pinacoid and only slight development of the hexagonal prism. The beautiful white crystals from Wheal Wrey, associated in some cases with iron pyrites in brilliant cubes, are either slender prismatic crystals like those in Nos. 720 to 722, or stout prisms as in No. 724. Careful examination will show that what looks like a hexagonal prism is often a very acute rhombohedron, the faces not being * Journ. Roy. Inst. Corn., vol. xii. (1894), p. 54. t " Manual of the Mineralogy of Great Britair, etc.," p. 36. 94 MINERALS OF CORNWALL AND DEVON. parallel-sided. Two generations of calcite crystals may be noted in some of the specimens, as in No. 723, where the larger crystals are apparently impaled by the slender prisms, to which they are therefore subsequent. In Nos. 728, 729 the calcite appears in sheaf - like aggregates of crystals, on a base of red quartz with a thin coating of secondary quartz and a sprinkling of pyrite. The beautiful snow-white calcite of Herodsfoot (No. 732) in polysynthetic crystals is likewise associated with quartz and pyrites. In No. 741 the calcite is pink, in consequence of a little associated iron or manganese. Calcite, by reason of its ready solubility in carbonated waters, is a mineral of great mobility, being easily removed from one situa- tion and deposited in another. Waters containing sulphuric acid from decomposed mundic will remove the lime as sulphate, and tend to deposit it as gypsum. No. 742 is a specimen of finely crystallised selenite from a gypseous deposit in a boiler near Redruth, which was fed with water containing sulphate of lime in solution. Dolomite (Nos. 743 to 746). Calcite is subject to some variability in chemical composition by the replacement of its calcium to a greater or less extent by other divalent metals, notably by magnesium. When a considerable proportion of magnesium is present, the spar frequently displays a pearly lustre on the faces of the crystal, whence it is known as pearl spar. If the two carbonates be present in equal molecular proportion, the resulting compound is the double carbonate termed Dolomite. In specimen No. 743 the spar exhibits not only the nacreous lustre but the characteristic curvature of the faces, the curvature becoming so pronounced as to produce " saddle-shaped " crystals. Here the dolomite is seated on quartz, well crystallised and slightly amethystine in tint, and is itself sparsely sprinkled with pyrites. No. 744, from Menheniot, shows the following sequence of deposits viz. : (1) quartz; (2) fluorite; (3) second growth of quartz; (4) dolomite ; (5) pyrite. The fluor is in blue cubes ; the quartz of the second generation is in very small clear sharp crystals ; and the opaque white dolomite is in rhombohedra, which have their faces slightly curved and distinctly pearly, as seen also in Nos. 743 and 745. In No. 745, from Beer Alston, in Devon, the succession is simpler, being (1) fluorite, (2) chalybite, and (3) dolomite. No. 746 is note- worthy for its well-formed rhombohedra, different from the lenticular crystals on some of the previous specimens. Dolomite has been formed artificially in various ways : for example, by heating carbonate of lime with a magnesian solution, such as the bicarbonate or the chloride. Even at 100 C. dolomite may be so formed, but a higher temperature favours the reaction.* Dolomite * F. Hoppe-Seyler in Zeitsch, f. GeoL, vol. xxvii. (1875), p. 495. BARYTES. 95 has also been detected as a natural precipitate from certain mineral waters.* The subject will be again referred to. Barytes (Nos. 747 to 758.) Although Barytes, or sulphate of barium, is a very common mineral in the veinstones of the north of England, it is remarkably rare in Cornwall, even in the lead-lodes. Formerly one of the chief localities for Cornish barytes was the mine in Gwennap called Ale and Cakes, afterwards one of the " United Mines," and subsequently absorbed in the Consolidated Group. Here the mineral occurred in a copper lode, at a depth, according to Mr. Garby, of 170 fathoms from the surface.f Nos. 755 to 757, from this locality, show the characteristic greenish grey colour of the crystals, and their aggrega- tion in sheaf -like groups. The crystals tend to become darker in colour on long exposure to light. J Some of the silver-lead mines in the neighbourhood of Liskeard have yielded beautiful specimens of barytes in sharply denned crystals of yellow colour, brilliant lustre, and tabular habit ; witness the specimens Nos. 747 to 754, from Wheal Mary Ann, in Menheniot. Iron-pyrites occurs here in association with the barytes ; and its de- composition may have furnished sulphuric acid to the waters of the mine, so that on meeting a solution containing any barium salt, the almost insoluble sulphate would be precipitated. In No. 753 the following succession of minerals is shown : (1) fluor-spar in sea-green cubes ; (2) quartz in white prisms ; (3) barytes in pale brown tabular crystals. The pink barytes, No. 758, is from Babbicombe in Devon, where it occurs in the limestone. Further remarks concerning barytes may be conveniently deferred until the more typical examples from other localities come under review (pp. 168, 186). DIVISION 2. MINERALS OF CORNWALL AND DEVON. MISCELLANEOUS MINERALS. (Nos. 759 to 826). A number of Cornish and Devon minerals which could not, with regard to scientific propriety, be placed in any of the foregoing classes are here grouped together as a miscellaneous assemblage, brought into association only by their local occurrence. They form a group with no pretence to homogeneity, either chemical or geo- logical, including as they do such diverse minerals from such varied formations as wavellite from the Carboniferous shales, calcite from the Devonian limestone, various silicates from the altered * Comptes Rendus, vol. c. (1888), p. 665. t Trans. Roy. Qeol. Soc. Corn., vol. vii. (1865), p. 81. j J. H. Collins 4 " Handbook," p. 13. 96 MINERALS OF CORNWALL AND DEVON, killas, felspars from the granite, and garnets and other minerals from the greenstones, with a few other substances obtained from certain lodes but hardly suitable for exhibition in any of the pre- ceding series. Although these minerals could not be appropriately placed elsewhere, it seems necessary to exhibit them in order to bring the collection within some reasonable approach to completeness as representative of the mineral resources of Cornwall and Devon. Chalcedony (Nos. 759 to 776). Silica occasionally occurs in veins in the condition of Chalcedony, but although this is chemically identical with quartz it could hardly be placed by the side of that mineral, in the group of spars, inas- much as it is not apparently crystalline, and crystalline structure is an essential characteristic of a " spar." Instead of forming crystals, chalcedony usually occurs in masses which are mammillary, botryoidal, or stalactitic in form. Yet, when examined in thin sections under the microscope, the chalcedony is seen to possess a crystalline structure, being composed of fibres, which differ however in optical characters from true quartz. Hence chalcedony is re- garded as a crypto-crystalline or micro-crystalline variety of native silica. Very beautiful examples of stalactitic chalcedony were formerly obtained from the Trevascus mine, in the parish of Gwinear, and some are here exhibited which show admirably the delicate and even fanciful shapes of the specimens from this locality (see notably Nos. 759, 760, 763, 770). Many other examples of rather similar char- acter are shown from Pednandrea, near Redruth (Nos. 767 and 768). These specimens sufficiently illustrate the characteristics of the mineral its grey yellow or brown tints, its translucency, its rather waxy or resinous lustre, and its conchoidal fracture. It is notable that the surface is coated in some cases with a bluish bloom, of much delicacy and beauty, as seen on Nos. 765 and 766. Other specimens of chalcedony, perhaps still finer, are exhibited in the Ludlam collec- tion in the Hall, Case IV. The forms of chalcedony at once suggest that it has been deposited from siliceous solutions ; and it was formerly supposed that a little opal, or soluble hydrated silica, was often associated with the fibro- crystalline mineral, thus causing the chalcedony to have a slightly lower density than that of quartz. In No. 772 a chalcedonic sub- stance, scarcely, if at all, distinguishable from true flint, from the Chalk, has been deposited in a brecciated copper-lode, with chalco- pyrite, siderite and ' peach.' Chalcedony sometimes forms a coating over crystals of quartz and other minerals, as shown in Nos. 761 and 762. On the removal of the invested mineral, the chalcedonic crust may be left as a hollow shell, such as is seen in No. 773. Here the angular cavities in the chalcedony represent the shape of the mineral removed, apparently in this case fluorspar. True pseudomorphs of chalcedony are not uncommon, and in No. 774 the mineral has assumed the form of a CHALCEDONY. 97 fine octahedral crystal of fluor. The material of such pseudomorphs is often described as hornstone. In some cases the fluor is simply invested, but in others completely replaced, by the chalcedonic mineral. The remarkable pseudomorphs known as Haytorite (No. 775) are composed of chalcedonic silica which has taken the form of datolite. According to Geinitz, who examined the material microscopically, the pseudomorphism was effected by gradual change and not by envelopment. Datolite is a basic silicate of boron and calcium, sometimes regarded as a boro-silicate of lime. Dr. Busz has detected datolite with garnets, in the limestone of South Brent in Devonshire*; but though now extremely rare as a British mineral it must have existed in large crystals when these fine pseudomorphs were formed. Haytorite takes its name from the locality on Dartmoor, where it was discovered. The Haytor iron mine yielded not only haytorite, but also pseudomorphs of chalcedony after calcite. The magnetic iron ore of this mine has already been referred to (p. 66). Haytorite has likewise been recorded from North Roskear Mine, in Cornwall. Beekite (No. 776) is an orbicular form of chalcedony, named after Dr. Beek, Dean of Bristol, who first called attention to it, as an incrustation on fossils in South Devon. It was described by the late Mr. W. Pengellyf and analysed by Professor Church.J Beekite generally appears either as a deposit of silica in concentric annular masses on corals and other fossils, or as a pseudomorphic replace- ment of them, but it occurs also on fragments of limestone which are not distinctly organic. Prof. T. McK. Hughes regards the beekite as chalcedonic chert formed as a thin layer just beneath the surface of the limestone, and revealed only on removal of the external crust : the siliceous material then exposed may form a hollow shell so thin as to float on water, and in some cases enclosing loose earthy matter which rattles when shaken. Certain siliceous minerals more or less akin to chalcedony, but differing generally in optical characters, have been discriminated by the microscopic investigations of French mineralogists in recent years, and have received distinctive names, such as lussatite, lute- cite, quartzine and pseudo-chalcedonite.|| Opal, or hydrated silica deposited in a colloidal state as an amor- phous mineral, less hard and less dense than quartz, is by no means common in the West of England. No. 777 is an interesting specimen showing opal in association with cassiterite,. This specimen from Trumpet Consols, near Helston, was presented by the late Sir W. W. Smyth, F.R.S., and shows the opal as a milk-white and pale blue translucent mineral. * Geol Mag., 1896, p. 492. N. Jahrb f. Min., 1899. p. 90. f " On the Beekites found ir the Red Conglomerates of Torbay." Bep. Brit. Assoc., 1856, p. 74. J Phil. Mag. [iv.], vol. xxiii., p. 95. " On the manner of occurrence of Beekite and its bearing upon the origin of siliceous beds of Palaeozoic age." Min. Mag., vol. viii. (1889), p. 266. || See Prof. Lacroix, " Mineralogie de la France," vol. iii. (1901), p. 120. 7882. H 9fl MINERALS OF fORNWALL AND TVEVON. In connection with the formation of opal, chalcedony and quartz in mineral- veins, it may not be out of place to call attention to an observation of Prof. Spezia, during the construction of the Simplon tunnel through the Alps. He obtained, from a fissure in the gneiss, a gelatinous substance, like vaseline, apparently a mechanical mixture of silicic acid and aluminium hydroxide, in a colloidal con- dition. Very minute crystals of quartz were embedded in the sub- stance, and it is suggested that this gelatinous silicic acid probably represents a stage in the formation of quartz.* Calcite (Nos. 778 to 783). The specimens of Calcite here grouped together could hardly find a place with the calcites already described from the lodes of Cornwall and Devon, inasmuch as they were obtained not from mineral-veins, but from limestone quarries. With the exception of No. 782, which is a specimen from Ashburton, all the calcites here exhibited are from the quarries near Plymouth, opened up a century ago to furnish stone for the construction of the breakwater. The Plymouth rag forms part of the Great Devon Limestone, which is referable to the Middle Devonian, or Eifelian, group of strata. Between 3,000,000 and 4,000,000 tons of limestone were extracted for Rennie's great structure from quarries at Oreston, about a mile from Plymouth. In the fissures of the rock, as is common in other limestones, crystals of calcite were found. Some of the specimens, as Nos. 778 and 779, show the crystals attached to the mother- rock ; whilst others, like Nos. 780 and 781, exhibit the crystals clustered around stalactites which have formed in cavities of the limestone. Some of the specimens, notably Nos. 780 and 781, possess a yellow colour, which has often suggested to quarrymen the name of sugar candy spar. The colour is no doubt referable to a trace of iron, much of the Devonian limestone being veined and clouded with ferruginous stains. In No. 783, from the Ilfracombe limestone, the carbonate of lime has been deposited in a coralloidal form, and appears to be in the condition of Aragonite. This species, though chemically identical with calcite, is slightly denser and harder, and when crystallised assumes forms of the orthorhombic system. (See p. 150.) Wavellite, etc. (Nos. 784 to 790). According to the late Mr. Townshend Hall, Wavellite was discovered about the year 1785 by Mr. I. Hill, of Tavistock.f Sir Humphry Davy, who examined it chemically in 1805, says, " This fossil was found many years ago by Dr. Wavel in a quarry near Barnstaple."J * Journ. Chem. Soc., vol. ii., 1901 (Abstracts), p. 393. t " On the Mineral Localities of Devonshire." Trans. Dtvon. Assoc.. vol. ii., Tartii., 1868, p. 332. % " An Account of Some Analytical Experiments on a Mineral Production from Devonshire." Phil. Trans, for 1805, p. 155. V !OF THE FELSPARS, ETC. !l ( , It was taken at first for a zeolite, but Davy was led to regard it as a hydrate of alumina and proposed to call it, from this false notion of its composition, hydrargyllite, though he states that Dr. Babington had suggested that it should be named wavellite after Dr. Wavel, of Barnstaple. The true nature of the mineral as a hydra ted phosphate of alumina was determined by Wavel. Wavellite occurs in black slaty rocks of the Culm- measures at Filleigh, between Barnstaple and South Moulton, in North Devon. As seen in Nos. 784 to 788, it forms small hemispherical masses, composed of radiating fibres of acicular crystals, of white, grey, brown, or bluish colour ; whilst in the narrow crevices of the rock it spreads out in the form of circular films, with a radiate structure. With these typical specimens from Devonshire, the visitor may compare the Irish wavellite, represented in Case XII. The species has also been found in Gower, in South Wales, by Mr. R. H. Tidde- man.* Tavistockite a rare mineral from near Tavistock, described by Prof. A. H. Church,f and represented by Nos. 791 to 793 appears to be a hydrated phosphate of aluminium and calcium. The speci- mens show its occurrence on quartz, with copper- pyrites in one case, and with fluor spar in another. Felspars, etc. (Nos. 795 to 800). In the fissures or drusy cavities of granitic rocks, the component minerals notably the felspar may occasionally be found in well- developed crystals. The specimen No. 795, from St. Austell, shows crystals of opaque white Orthoclase, or potash- felspar, associated with pale sea-green apatite, and the yellowish-green micaceous mineral called gilbertite. Minute cubes of pyrite are scattered sparsely over the felspar. In the tray numbered 797 are two large, thin tabular crystals of orthoclase, showing the composite twin forms known as " Carlsbad twins." Such crystals have the broad planes of the clinopinacoid well developed, and are said to present the " sanidine habit," since the variety of orthoclase called sanidine is typically tabular. The crystals here exhibited come from Caudle Down, St. Austell, and have suffered partial kaolinisation, so that they present a dead white appearance, with a rough, dull surface. Some of the por- phyritic granites of Cornwall exhibit very large crystals of white orthoclase, with a beautiful zonal structure marked by inclusions, as may be seen in several of the polished columns and other orna- mental objects in the Hall. The alteration of felspar with produc- tion of kaolin, or china-clay, has already been referred to (p. 10). The polished specimen, No. 798, from the Triassic conglomerate of Heavitree, near Exeter, displays the flesh-red crystals of a variety * Summary of Progress, Oeol. Surv. for 1901 (1902), p. 42. f Journ. Chem. 8oc. [2], vol. iii. (18(56), p. 263. 100 MINI RALS OF CORNWALL AND DEVON. of orthoclase, which was named by Levy, in 1827, after Sir Roderick I. Murchison (6. 1792, d. 1871).* Murchisonite is notable for the peculiar sheen, oi^schiller, which it exhibits on one of its cleavage- planes. The mineral may possibly be an altered felspar from the granite of Dartmoor. Crystals of Albite, or soda felspar (No. 799) are sometimes found studding the walls of fissures in the Devonian slaty rocks of North Cornwall. Excellent crystals occur, in association with quartz and calcite, in the joints of the slates at Tintagel. The minerals of this locality have been well described by Mr. H. L. Bowman.f On the albite of Lanterdan Quarry, Prof. Miers discovered Mona- zite J a phosphate of the rare cerium metals, which in recent years has been used in the preparation of mantles for incandescent gas- lights. Monazite is usually associated with titanium minerals, and it is therefore not surprising to find that needles of rutile are found with it on the Tintagel albite, whilst anatase occurs in the immediate neighbourhood. In the tray No. 800 are two specimens of Finite in a schorlaceous elvan from St. Hilary, in West Cornwall. Finite is a mineral not infrequent in the granites and elvans of the Land's End district ; and here, as elsewhere, it seems to be an alteration-product of cordierite. The cordierite is a silicate of aluminium and mag- nesium, with more or less iron, which readily suffers transformation into micaceous and other substances. In pinite, which is some- times regarded as an impure massive variety of muscovite, the form of the original cordierite is faithfully retained, so that the mineral seen in these specimens may be regarded as a true pseudo- morph. Mr. J. H. Collins has suggested that the Cornish pinite may in some cases be pseudomorphous after nepheline.!! Garnets, etc. (Nos. 801 to 808). Garnet is hardly to be regarded as an uncommon mineral in Cornwall, though good crystals are not of frequent occurrence. Some of the best occur in the cliffs in the neighbourhood of Botal- lack, in West Cornwall, whence the examples here shown as Nos. 801 to 802 have been obtained. These rather resemble the iron-alumina garnets known as almandine. They present a deep red colour so deep as to appear almost black in the stout crystals, but showing colour and translucency towards the edges. In form they are well- developed icositetrahedra or solids bounded by twenty-four * " On a New Mineral Substance proposed to be called Murchisonite." Phil. Mag., vol. L (1827), p. 448. f " On Monaaite and Associated Minerals from Tintagel, Cornwall," Min. Mag., vol. xii. (1900), p. 358. J " On Monazite from Cornwall," Min. Mag., vol. vi., 1886, p, 64. For the nature and formation of this mineral the following paper should be consulted : " Tho Natural History of Cordierite and its Associates." By J. J. H. Teall, M.A., F.R.S., Proc. Qeol. Assoc., vol. xvl, 1900, p. 61. i| " On the Pinite of Breage in Cornwall," Min. Mag., vol. x. (1894), p. 8, (3ARNET I CHLORITE, ETC. 10] trapeziums. These crystals are embedded in a dark amphibolite, or hornblende-schist, from which they are readily detached, leaving very sharp impressions in the matrix. Common garnet is now generally known as andradite, including the varieties sometimes regarded as allochroite and colophonite. No. 805, from St. Just, shows garnet of orange-brown colour, crys- tallised not very distinctly in rhombic dodecahedra, having the edges truncated by planes of the icositetrahedron, and associated with axinite. Somewhat similar garnet from Okehampton, in Devon, is seen in No. 803. In the specimen No. 804, from the old Belston Mine, near Oke- hampton, garnet is associated not only with axinite but also with copper-pyrites and mispickel. This unusual association, which was described by Sir W. W. Smyth, occurred in the metamorphic zone at the margin of the Dartmoor granite, where considerable workings for copper- ore were at one time carried on.* A similar specimen is in Case II., No. 159. The minerals were probably developed by contact-metamorphism. Among the changes which garnet undergoes that of conversion into chlorite is not uncommon. This is illustrated by the specimen No. 802. Here the crystals, while retaining their form, have become coated with a dull green chloritic mineral. The change generally occurs along microscopic cracks, the neighbouring garnet becoming less hard and dense, and gradually assuming a dull green appear- ance. Some fine pseudomorphs of chlorite after garnet are shown in the Wall Case 34, but these are not British specimens, f t, Chlorite is a general name applied to a number of minerals, more or less scaly in structure and greenish in colour. They form a rather ill-defined group, consisting of silicates of aluminium and magnesium, with iron, etc., and since they contain a large proportion of water they are sometimes termed hydromicas. The chlorites are usually alteration -products of felspars, garnet, mica, augite, hornblende, and other ferro-magnesian silicates ; but in certain cases chlorite may be an original mineral. By the Cornish miner chlorite is commonly called peach, and hence a chloritic lode is said to be " peachy." Whilst the green peach is undoubtedly of this character, it seems that blue peach is usually a form of tourmaline. The specimen No. 807 represents Cornish Actinolite, showing the radiating fibres of green colour and silky lustre characteristic of this form of amphibole. No. 808 is a representative specimen of the mineral known as Prehnite. This is a hydrated silicate of aluminium- and calcium, * " On the Occurrence of Metallic Ores with Garnet Rock," Journ. R. Oeol 8oc., Corn., vol. ix. (1878), p. 38. See also Solly in Min. Mag., vol. vi. ( 1886). For ore-deposits formed by contact metamorphisin, consult a valuable paper by W. Lindgren, " The Character and Genesis of certain Contact Deposits," Trans. Am. Inst. Min. Eng., vol. xxxi. (1902), p. 220. f On the alteration of garnet into chlorite see Am. Journ. Sc. [3], vol. x. (1875), p. 17, and vol. xxxii (1886), p. 307. 102 MINERALS OF CORNWALL AND DEVON. occurring in the cliffs near Botallack and at some other localities in St. Just. It will be subsequently noticed in connection with the fine specimens from Scotland (p. 216). Serpentine, etc. (Nos. 809 to 817). Among the various hydrous silicates shown in this case the most interesting is the mineral substance well known as Serpentine. This occurs, however, as a rock rather than as a definite mineral species. Several specimens of the beautiful rock from the Lizard district are placed here, under the numbers 809 to 813, and others are exhibited in Section IV. of the Horse-Shoe case ; whilst a number of objects in the Hall of the Museum show the material worked as an ornamental stone in the form of columns, vases, etc. The origin of the Lizard serpentine has been specially studied by Prof. Bonney, who showed many years ago that it had been formed from the alteration of intrusive igneous rocks.* Serpentine usually results from the metamorphism of rocks rich in olivine, like the peridotites. Olivine, which is a silicate of mag- nesium, with more or less iron, is a mineral very prone to alteration. Its conversion into serpentine, a hydrous silicate of magnesium, can be traced as it proceeds along the cleavage cracks and curved fissures of the crystals. Pseudomorphs of serpentine after olivine are well known. Opaque granules of magnetite are usually present, and represent the iron eliminated from the olivine during serpentinisation ; or the iron, passing wholly into the ferric state, may make its appear- ance as haematite or as limonite. The conversion into serpentine is accompanied by considerable increase of volume (above 30 per cent.), and probably involves reactions more complicated than simple hydration. It was shown many years ago by the brothers Rogers that silicate of magnesium may be decomposed by carbonated waters.f This conclusion was confirmed by the experiments of Mr. A. Johnstone, of Edinburgh, who observed that water charged with carbonic acid attacks olivine. J Magnesium carbonate, or Magnesite, occurs in white veins and patches in the Lizard serpentine. The production of magnesite from serpentine evidently involves dehydration. Mr. Howard Fox called attention some years ago to a substance curiously like flint, occurring as veins in the serpentine of Kynance Cove, and an analysis by Mr. Hort Player showed it to be the mineral called pseudophite.% This mineral may, perhaps, be placed in the chlorite group (No. 815). * See especially his papers in Quart. Journ. Geol. Soc., vol. xxxiii. (1877), p. 884; and vol. xxxiv. (1878), p. 769; Geol. Mag. n.s. [2], vol. vi. (1879), p. 362 ; and [3] vol. i. (1884), p. 406. See also Gen. M'Mahon's address " On the Manufacture of Serpentine in Nature's Laboratory," Proc. Geol. Assoc., vol. xi. (1890), p. 427. Also: "British Petrography." By J. J. H. Teall, 1888, p. 104. | Amer. Journ. Soc. [2], vol. v. (1848), p. 401. | " On the action of carbonic acid water on olivine." Proc. Roy. Soc. Edin., J888. Jfm. Mag., vol. ix (1892), p. 275. ALLOPHANE, ETC. 103 Steatite, or soapstone (No. 816) occurs in the Lizard serpentine, and was at one time worked as a material for the manufacture of porcelain, as also as a source of various magnesian salts. It is a hydrous magnesium silicate, and may be regarded as a massive variety of talc. Saponite (No. 817) is a somewhat similar mineral, but contains much aluminium silicate. With the Cornish serpentine is placed a specimen of Diallage (No. 814) from the gabbro of Crousa Downs, not far from the Lizard.* The rock called gabbro is a crystalline aggregate of diallage and plagioclase felspar, with olivine. The dead- white mineral in the coarse gabbro is saussurite, an alteration-product of the plagioclase, whilst the diallage, which is a variety of augite, is distinguished by the bronzy lustre displayed by what appear to be its cleavage planes. These represent directions of chemical weakness along which the mineral has suffered that kind of alteration which Professor Judd has distinguished as schillerisation.'f Microscopic lamellar enclos- ures have been developed along these planes of parting, and to these secondary minerals the metalloid lustre, or schiller, of the diallage is due. Allophane, etc. (Nos. 818 to 824). Several amorphous silicates of aluminium are here grouped to- gether. The specimens 819 and 820, which attract the eye by their delicate blue colour and pearly lustre, are examples of the hydrated aluminium silicate termed Allophane. In these specimens the mineral occurs in small botryoidal masses, on black carbonaceous shale, from Wheal Hamblyn, near Bridestone, in Devonshire. The blue colour is due to admixture with some copper mineral, probably chrysocolla, as the cupreous allophane is said to pass in some cases into this copper silicate. The opaline allophane, like these speci- mens, has been distinguished as Schrotterite. In No. 818 the allophane is tinted green, presumably by malachite, and is partially encrusted with brown hydrated oxide of iron, associated with a little native copper, in delicate sprigs, coated with the green carbonate. Allophane seems always to be a secondary mineral derived from various aluminous silicates, especially felspars. It is not infrequent in certain copper mines. The massive opaque substance generally called Lithomarge is re- presented by Nos. 821 and 822. Some of the Cornish " lithomage " may be referred to the species halloysite. In No. 822, from Tucking- mill, near Camborne, the white substance is marked with irregular stripes of purple colour. No. 823 represents the mineral from Restormel, which Prof. Church has distinguished as Eestormelite.\ * For description of the Crousa Down gabbro see " British Petrography,'* by J. J. H. Teall, M.A., p. 174. t On schillerisation see Prof. Judd's papers in Quart. Journ. Geol. Soc., vol. xli. (1885), p. 383 ; and Min. Mag., vol. vii. (1887), p. 81, ^ Journ. Chem. Soc., Vol. xxiii., (1870), p. 165. 104 MINERALS OF CORNWALL AND DEVON. The earthy substance, of dull green colour, numbered 824, is a sample of Chloropal from Hay tor in Devonshire. This is a hydra ted silicate of iron. Pigotite (No. 825). Under the name of Pigotite, Prof. Johnston, of Durham, described in 1840 a Cornish mineral which he regarded as a compound of alumina with an organic acid termed by him mudesous acid.* To this body, in its anhydrous condition, he assigned the formula C 12 H 5 8 . It was assumed that the acid had resulted from the decay of superficial vegetation on the moorland,f and having been carried down to a mass of decomposing granite had attacked the felspar. The product was found as an incrustation on the walls of certain caves in granitic cliffs in Cornwall. The specimens here exhibited from St. Levan, which have recently been presented by J. W. Wetherell, Esq., rather resemble a dark brown wood- opal. { The name was given to the mineral in compliment to the Rev. M. Pigot, who, with Prof. Johnston, first observed it. Retinite (No. 826). Associated with the Tertiary lignite of Bovey Tracey, in Devon- shire, there are occasionally found small irregular masses of a brown resinous substance, usually earthy in appearance, such as the speci- men No. 826. This substance was examined by Hatchett, who named it Retinasphatt, since he regarded it as partly resinous and partly bituminous. Subsequently it was analysed by Prof. J. F. W. Johnston of Durham.ll It is now usually designated Retinite, and appears to be a fossil resin exuded from the coniferous trees which contributed to the formation of the Bovey coal. The characteristic conifer is the Sequoia coutisice of Heer, a tree allied to the mammoth tree of California.^ It may be noted that the term ' retinite ' is now used as a rather general name for a number of fossil resins more or less akin to amber, but usually occurring in lignite. Various mineral hydrocarbons, including petroleum, have occa- sionally been found in some of the mines of Cornwall and Devon, and carbon in the form of Graphite is not unknown, as witnessed by specimens in the Horse-shoe Case Section A. The collection of British Minerals is continued in Case VII. , on the opposite, or eastern, side of the Museum. * " On the constitution of Pigotite, and on the Mudesous and Mudesic Acids." Phil Mag., vol. xvii. (1840), p. 382. f Hence the name, from juu&). May., 1.SJM-, p. r>67. COLD, tiTO. ~> is well known tKat rutile, and to a less extent anatase, are widely distributed as microscopic constituents of slates, clays and other sedimentary rocks (seep. 191). Some of the finest crystals of British Quartz are obtained from the neighbourhood of Snowdon. The examples here exhibited (Nos. 891, 892) show that while some of this quartz may be pellucid as rock crystal, other specimens are slightly opalescent and may acquire a certain whiteness and opacity, sufficient to justify their suggestive name of milky quartz. No. 893 is a specimen of the well-known Jasper of Carnarvon- shire, which has occasionally been worked as an ornamental stone. In the Horse-shoe Case will be found some fine examples of Asbestos, or fibrous hornblende, a mineral which occurs as veins in the rocks of Moel Hebog, near Snowdon, and has been used industrially. Welsh Gold (No. 894). Mention has already been made (p. 18) in connection with the Cornish tin-ore of the wide distribution in minute quantity of Native Gold. Scattered more or less sparingly through the quartz-veins in many parts of Wales, the metal is set free on the disintegration of these veins at their outcrop, and by its density tends to accumulate in local depressions, after the associated quartz has been swept away by running water. Keltic tradition, not unsupported by archaeological discovery, points to the rather profuse use of Welsh gold at a very remote period.* Nor is this unreasonable. The early settlers in the country might no doubt find much gold in the alluvial deposits, not necessarily because the auriferous veins were then richer than they now are, but rather because the materials of these veins had been subjected during long periods of time to natural pro- cesses of washing and dressing, so that the produce of ages might be found in a concentrated form. If alluvial gold satisfied the wants of the prehistoric inhabitant of what is now Wales, the Roman invader was bold enough to attack the obdurate reef itself. Remains of workings, reputed on high authority to be Roman, still exist at Gogofau, near Lampeter, in Carmarthenshire, showing that gold was extracted with much labour from the quartz-lodes. Iron-pyrites is the principal metallic mineral, but free gold was detected by the Geological Survey ors.f In modern times, much attention has been directed to the gold- bearing rocks of Merionethshire, where veins of quartz, occasionally with calcite, carry iron-pyrites, copper-pyrites, zinc-blende and galena, associated with more or less gold. According to Sir A. C. Ramsay, the lodes run through the Lingula flags and Cambrian grits, especially in the neighbourhood of intrusive rocks, and in association * See, for instance, an " Historical Account or an Inquiry into the Situation of the Gold Mines of the Ancient Britons." Cambrian Register, vol. iii., p.31. t Notes on the Gogofau, or Ogo-fau, Mine, near Pumpsant, Carmarthen- shire." By Warington W. Smyth, M.A. Mem. Geol. Surv., vol. i. (1846), p. 480. 130 WELSH GOLD. with certain rocks of talcose character.* Sir W. W. Smyth pointed out the interesting fact that the gold is accompanied by tetradymite, or telluric bismuth a mineral which occurs in companionship with gold at several other localities.*)* Many illustrations of the occur- rence of Welsh gold will be found in Wall-case I !. Attention was called in 1843 by the late Mr. Arthur Dean to his discovery of gold at Cwm Eisen, a mine which had been previously worked for lead.J This announcement led to extended search, resulting in the detection of gold over a wide district, notably between Dolgelly and Barmouth, and in the alluvial deposits in the valley of the Mawddach. Operations were carried on at several mines, some of which, like the Vigra and Clogau, were on lodes pre- viously worked for copper. These workings, however, were con- ducted for many years on a comparatively small scale, and were only intermittently productive until Mr. Pritchard Morgan, returning to Wales with a knowledge of gold mining acquired in Australia, under- took operations of a bold character at Gwynfynydd. At the present time gold mining is carried on at St. David's mine, formerly the Clogau, near Dolgelly ; at Gwyn, formerly the British Goldfields, Gwynfynydd ; at Ffridd Goch, Dolgelly ; and at Cefn Goch, Tynygroes. According to the official statistics, these workings yielded during the year 1902 a total quantity of 29,953 tons of gold ore, of the estimated value of 12,621. The amount of gold ex- tracted from this ore was 4,181 ozs., and its value 14,570. These returns show a serious decline in the output. Thus, in 1900 the amount of Welsh gold obtained during the year was valued at 52,147. Analyses by the late Mr. David Forbes showed that a specimen of gold from the Clogau lode contained upwards of 9 per cent, of silver, the native metal thus corresponding to an alloy of the com- position Au G Ag ; whilst a sample of stream gold from the Mawddach yielded as much as 18' 99 per cent, of silver. || When the proportion of silver in native gold reaches 20 per cent., the alloy is called Electrum. The association of the Welsh gold with iron-pyrites and in some cases with brown ochreous oxide of iron resulting from the alteration of the sulphide, suggests that here, as in so many other localities, the precious metal may have been originally brought up, from a plutonic source, with the pyrites and set free on its decom- position. * " On the Geology of the Gold-bearing district of Merionethshire, North Wales." By Prof. A. C. Ramsay. Quart. Jour. Geol. Soc., vol. x. (1854), p. 242. Also Geol. Surv. Mem. " Geology of North Wales," p. 59. t " Gold Mining at Clogau, North Wales." Mining and Smelting May., vol. i. (1866), p. 359. J Rept. Brit. Assoc. York (1844), p. 56. " Mines and Quarries : General Report and Statistics for 1902." Edited by C. Le Neve Foster, D.Sc., F.R.S. (1903), p. 210. 1! " Researches in British Mineralogy." Phil. Mag. (1867), p. 329. MINERALS OP DERBYSHIRE. 131 DIVISION 2. MINERALS OF DERBYSHIRE. THE SPARS (Nos. 805 to 0(>2.) Metal-mining in Derbyshire, though now declining in importance, is a very ancient industry, which was directed originally to the extraction of the ores of lead, and subsequently to those of lead and zinc. The ores consisting of the normal sulphides, galena and blende, with their alteration-products are associated in the ore- deposits of Derbyshire with calcite, fluor-spar and barytes. Three types of ore repositories are recognised the rakes, the pipes and the flats. These seem to represent fissures, varying in magnitude and direction, in the Carboniferous Limestone, which forms the char- acteristic rock in the mining districts of the county. Channels for the passage of water through the limestone are formed by the planes of jointing, bedding, and faulting ; and the solvent action of the circulating liquid produces irregular cavities which may become receptacles for ore. It is probable, too, that here as in many other limestone districts, the ore may, in some cases, have been substi- tuted for the calcareous rock by a process of molecular replacement. The ore-deposits are said to be most numerous and most productive in the upper part of the limestone, some of the richest bodies of ore having been found immediately under the Yoredale shales.* Interstratified with the limestones there are occasional sheets of basic eruptive rocks, usually olivine-dolerites, known locally as toad- stone, and in many cases representing contemporaneous lava flows. (* The old belief that the mineral-veins disappear in the toadstone has often been disproved, though it remains a fact subject, however, to occasional exception that the veins tend to become thinner and to suffer impoverishment when they pass into the igneous rock. It is generally held that the toadstone owes its name to its barren character, the word being a corruption of Todtstein, or " deadstone." German miners, or as old writers sometimes call them, " Dutch mineral men," were occasionally brought over to this country for the sake of their expert knowledge, and it is not unlikely that they should apply such a name to a rock in which the ore died out. The Rakes, or Rake veins, of the Derbyshire mines are deposits in fissures representing joints in the limestone, more or less vertical in direction, and sometimes corresponding with faults. The ore occurs * On the Geology of the district and on the Occurrence of the Ores, see Mem. GeoL. Surv. "North Derbyshire." By A. H. Green, C. Le Neve Foster, and J. R. Dakyns. 2nd Ed. (1887). By A. H. Green and A. Strahan. t See "The Ancient Volcanoes of Great Britain." By Sir Archibald Geikie, F.R.S. (1897), vol. ii., p. 8. And important papers by Mr. H. H. Arnold -Bemrose in Quart. Journ. Oeol. Soc. t vol. 1. (1894), p. 603; vol. Iv. (1899), pp. 224, 239. 13:2 MINERALS OF DERBYSHIRE. * either in parallel ribs, alternating with bands of veinstuff, or in isolated masses scattered through the sparry matrix. The term serin is applied to a string, or small rake ; and in some cases a mass of limestone may be traversed by a network of these veinlets, con- sisting of galena. Much of the lead-ore occurs, however, in the so-called Pipes, or pipe veins, which are deposits in cavities widened by erosion in the inclined direction of the beds of limestone, and connected one with another by means of leaders running along joints. Another mode of occurrence is that of Flats or flat veins, a name given to irregular sheet-like masses of ore disposed along the planes of bedding. It is found convenient to exhibit the metallic minerals in the following Case, No. VIII., so that the series in Case VII., now under notice, is limited to the three sparry minerals which form the principal veinstuff of the Derbyshire deposits namely calc spar, or calcite, fltior-spar, or fluorite, and heavy spar, or barytes. Odette (Nos. 895 to 938). Where ore-deposits occur in limestone, like those of Derbyshire, Calcite is likely to be a common mineral, crystallising in any free cavity, whether in the veinstone or in the neighbouring rock. Some of the finest known crystals of this species have been brought to light from the lead-mines of Derbyshire. A rather extensive series of specimens is here exhibited, sufficient to give some notion of their beauty and variety of form, but the specimens are necessarily of small size, and the visitor should consequently turn to the Horse- shoe Case (Section I.) in order to realise the magnitude attained by some of the Derbyshire crystals, especially the large yellowish scalenohedra. Calcite presents an unparalleled wealth of crystalline forms. The most characteristic of the Derbyshire crystals have a scalenohedral habit, and are known from their sharp-pointed extremities as Dog- tooth spar (Nos. 895 to 906). The scalenohedron is a solid bounded by twelve scalene triangles, and having the lateral edges rising and falling in a zig-zag manner, like those of a rhombo- hedron. Other crystals assume a prismatic habit, the six-sided prism being often terminated by the faces of a rhombohe- dron or of a scalenohedron (Nos. 907 to 910). In some cases, as in No. 911, the crystals are very complex, being highly charged with faces. Twin crystals are of frequent occurrence. It is not uncommon in Derbyshire specimens to find scalenohedral crystals having re-entrant angles, producing notches in the equatorial belt, showing that the scalenohedron is twinned on the basal pinacoid (No. 897). But the most interesting twinned crystals are those found many years ago at Eyam and known as butterfly twins (No. 917). These are in some cases quite heart-shaped, constituting the type which de Bournon called " la charmante macle " " chaux carbonatee en ccour." * They are scalenohedra twinned on a plane * " Traita de Mineralogie," vol. ii. (1808), p. G6. CALCITE. 133 of the rhombohedron. The Eyam twins are rather rare in collec- tions, but similar crystals of larger size have been discovered in recent years in the haematite mines of the North (p 149), and are comparatively common. Whatever the form assumed by calcite, the crystal always offers perfect rhombohedral cleavage. No. 912 is a cleavage rhombo- hedron ; but this fundamental form is rarely assumed independently by British calcite, or for the matter of that, by any calcite, except that from Iceland. The cleaved specimen No. 912 presents a delicate yellow colour, due probably to the presence of iron. In the columnar crystalline specimen No. 932 the yellowish colour is very pronounced, giving the substance the tint of sugar candy. Most of the Derbyshire calcite, however, is colourless or dead white. The opaque white spar from some of the mineral-veins in Derbyshire is crushed, and employed for making paths.* Cavities in the fossils of the carboniferous limestone are sometimes lined with beautiful crystals of calcite. No. 933, for example, is a Derbyshire specimen, showing a crop of such crystals, studding the inner shell- wall of the valve of a Productus. Another example is furnished by No. 934. The specimen of stalagmite, or dripstone, No. 935, illustrates the formation of a calcareous deposit, in layers, from solution in water. Meteoric waters, charged with carbonic acid, filter through the limestone and drain along the planes of jointing and bedding, dis- solving the rock by forming a soluble acid calcium carbonate, or bi-carbonate of lime. The loosely associated carbonic acid is readily eliminated from this compound, by elevation of temperature, or by exposure to air, or by the action of living vegetation, and the cal- careous salt is thereby reduced to the condition of the normal or neutral carbonate, which is but very sparingly soluble in water, so that it is easily precipitated. In recent years much attention has been given to organic action in determining the deposition of cal- careous matter ; and the researches of Dr. Cohn, Mr. W. H. Weedf and others tend to show that algous growths and other forms of plant life are frequently instrumental in causing precipitation, even in the calcareous sinter of hot springs. No. 937 is a specimen of tufa encrust ing C hara, deposited by the calcareous waters of Matlock in Derbyshire. It should be added that organic acids, derived mainly from decomposing vegetable matter, greatly assist in the solution of limestone-rocks. Some of the coral-like deposits of carbonate of lime, like No. 938, consist of Aragonite. It is generally held that the temperature at which deposition occurs is an important factor in determining whether the deposit shall take the form of calcite, or of the harder and denser aragonite. This subject will be again referred to (p. 150). * Mem. Geol. Surv., North Derbyshire (1887), p. 103. t "Formation of Travertine and Siliceous Sinter by the Vegetation of Hot Springs." By Walter Harvey Weed. Ninth, Ann. Hep. U.S. Gcol. Surv. (1889), p. 613. 134 MINERALS OF DERBYSHIRE. Dr. G. P. Merrill has shown that many stalagmitic deposits com- monly regarded as aragonite really consist of carbonate of lime in the normal form of calcite.* Elaterite, etc. (Nos. 939 to 942). The curious soft substance represented by No. 939 is known as Elaterite, elastic bitumen or mineral caoutchouc names which are sufficiently suggestive of its characters. It appears to have been first noticed about the year .1786 at the Odin Mine, near Castleton, one of the oldest mines in the country. Scientific attention was not called to it, however, until 1797, when Mr. C. Hatchett, who had made a special study of bituminous minerals, described it as a new species of bitumen, much resembling in elasticity and colour " the substance known by the name of cahoutchou (sic), or india-rubber. "f According to Prof. J. VV. F. Johnston, who analysed three specimens from Derbyshire, the origin of the substance is probably attributable to the effect of heat exerted by igneous rocks on the organic matter of the Carboniferous Limestone, whereby volatile products were evolved and condensed in the cooler rocks. J The substance has also been found near Windy Knoll. In the specimens Nos. 941, 942, hard brittle bitumen, or asphalt, is seen occurring in the form of small globular masses, with dog-tooth calcite, and blende, on fluor limestone. The form of this asphalt suggests that it represents solidified drops of a substance once liquid. Petroleum, or rock oil, sometimes oozes from the rocks, and explosive gases have often occurred in the lead mines. Such bituminous substances, representing probably the organic matter of the Carboniferous rocks, invite the suggestion that they, or kindred substances, may have played some part in the process of ore-formation by acting as reducing agents, and thus determining the formation of metallic sulphides, like galena, blende and pyrites, from solutions of the sulphates. The importance of bituminous substances, and even of the small proportion of organic matter in limestone, as reducing agents in the formation of ore-deposits, has been recently insisted on by Dr. W. P. Jenny.JI Fluorite (Nos. 943 to 954). In connection with the fine specimens of Fluorspar, or fluorite, from the West of England mines, exhibited in Case V. (p. 85), so much has already been said about this species that the Derbyshire * "The Onyx Marbles." By George P. Merrill. Rep. U.S. Nat. Muff, for 1S93 (1895), p. 539. t " Observations cm Bituminous Substances, With a Description of the Varieties of the Elastic Bitumen." Trans. Linn. Soc., vol. iv. (1797), p. 129. J "On the Composition of Certain Mineral Substances of Organic Origin. V., Elastic Bitumen of Derbyshire." Phil. Mag., vol. iii. (1838), p. 22. Oeol. Surv. Mem., North Derbyshire, p. 164. ji "The Chemistry of Ore-deposition." Trans. Am. Inst. Min. Eng., vol. xxxiii. (1903), p. 445. FLUORSPAR, ETC. 135 specimens displayed in this part of the Collection call for little remark. The spar occurs in many of the lead-mines as a gangue- mineral, or constituent of the vein-stuff, and is raised to a limited extent for use as a fluxing agent in metallurgical operations (whence indeed its original name, from fluo, to flow). It is also employed in the manufacture of a milky glass, in the production of hydrofluoric acid for etching glass, and as a source of various fluorine-compounds for laboratory use ; nor must its value as an ornamental stone be forgotten. In the year 1902 1,297 tons of the spar, valued at 1,584, were raised in Derbyshire. Of all kinds of Derbyshire spar the most beautiful is the purple fluor known as " Blue John," a name apparently correlative with " Black Jack," the miners' common name for zinc-blende. The specimens here shown illustrate the colour and structure of this spar (Nos. 953, 954). It is found almost exclusively near Castleton at the famous " Blue John Mine," situated on the side of Tray Cliff, in the midst of the wild scenery of the Peak. It is generally found in nodular masses, with a fibrous and concentric structure, enveloped in a clayey matrix occupying a fissure or pipe. The clay may re- present the insoluble residue left by removal of the limestone in solution.* The dark brownish purple fluor is called by the workmen "bull beef," but the colour is greatly altered, and a beautiful amethystine tint produced, by exposure to heat or by other artificial treatment. Where the spar crops out in the rocks, the " changing " is effected by the natural heat of the sun, and the dark blue fluor acquires a purple colour. The spar at the Blue John Mine was first found by two miners named John Kirk and Joseph Hall ; and its use for orna- mental purposes dates from about 1770, when it was introduced by Mr. Robert Hall, of Castleton. t Many specimens of polished fluor from Derbyshire, including some fine vases, will be found in the Hall of the Museum. The grand amphora on a pedestal at the northern end of the Principal Floor (No. 27), presented by the late S. Addington, Esq., is believed to be the largest specimen of its kind in existence, measuring as it does as much as two feet eight inches in height. It was the work of Mr. Yallance, of Matlock. Barytes (Nos. 956 to 960). Sulphate of barium, forming the mineral known as Barytes, is very common as a matrix of galena in lead- veins which traverse lime- stone. Although it occurs as a gangue-mineral in Derbyshire it is rarely crystallised, and as far finer specimens are exhibited from the North, especially from Cumberland, any detailed notice of the species may be suitably deferred (see p. 168). * Geol. Surv. Mem., North Derbyshire, p. 162, where a figure illustrates the occurrence of the Blue John. t "Gem of the Peak: Part V., History of the Fluoispar, Ancient and Modern." By W. Adams. 4th Ed., 1845, 136 MINERALS OF DERBYSHIRE. Barytes is extensively used as a white pigment, and in 1902 Derby- shire yielded 334. tons of the mineral. This consists principally of the white earthy barytes known as cawk or caulk. Some notable varieties of barytes occur in Derbyshire. A white arborescent barytes, with brown earthy oxide of iron, formerly found at Bonsai Moor, was known from its form as brainstone. No. 959 is a curious black variety of barytes, containing, according to an analysis by Prof. G. A. Kcenig, 3*1 per cent, of oxide of manganese.* The remarkable stalactitic barytes, found in every mineral collection, is illustrated by Nos. 956 to 958. This variety was first found in 1832, embedded in clay in a cross course on Arbellow, at Middleton, near Youlgreave. Transverse sections exhibit a beautiful radiated structure, with well-marked concentric rings, suggestive of the section of an exogenous tree stem ; and this structure, coupled with the rich brown colour, has led to its being popularly called " fossil oak." The zonal pattern displayed in section has also led to the rather unfortunate name of " onyx stone." It is used to a limited extent when cut and polished, as an ornamental stone, especially as a material in inlaid marble work. Quartz (Nos. 961, 962). Quartz is by no means common among the minerals of Derby- shire, t But in the neighbourhood of Buxton there are small crystals of quartz, generally found loose in the soil, and known as Buxton Diamonds. As seen in No. 961, the crystals present the form of hexagonal prisms, terminated usually at each end by a hexagonal pyramid. Whilst some are perfectly colourless, others are tinted brown, with oxide of iron. They appear to have been derived from such a source as is represented by No. 962, a specimen which shows similar doubly- terminated crystals in a matrix of flesh-coloured barytes. * Proc. Acad. Nat. Sc. Phil, for 1878 (1879), p. 99. f On quartz, see paper " On the Super-position of Quartz Crystals on Calcite in the Igneous Rocks occurring in the Carboniferous Limestone of Derbyshire." By W. F. Holroyd and J. Barnes. Trans. Mancli. Geol. jSoc., vol. xx vi. (1901), p. 46. LEAD-ORES. IT 7 CASE VIII. DIVISION 1. MINERALS OF DERBYSHIRE. THE ORES. Galena (Nos. 963 to 986). In this division of the Collection there is a fair display of the ores of Derbyshire, chiefly those of lead and zinc. Some of the lead-mines have yielded crystals of Galena exceptional in magni- tude and beauty. Thus, the Mill Close Mine, in Darley Dale, at present the most productive mine in Derbyshire, has furnished cubes of galena measuring two inches along the edge, with dog-tooth spar measuring a foot along the vertical axis of the scalenohedron.* The occurrence of fine crystals lining hollows in the veinstone, or studding the walls and roof of fissures in the limestone, suggests the deposition of galena in free cavities ; though its formation by molecular replacement of a calcareous rock is also to be frequently recognised where ores of lead and zinc occur in limestone (p. 164). The crystals of Derbyshire galena here exhibited show the mineral in cubes and octahedra, but mostly in combinations of the two forms, or cubo-octahedra. Some of the specimens present the characteristic cubic cleavage, and in No. 971 the cleavage face is marked diagon- ally by striations due to twin lamellae. The very brilliant metallic lustre of galena, which has led to its being called " the diamond among ores," is well displayed by such specimens as No. 972 ; but the lustre is usually lost on exposure, and in some cases the tarnish is brilliantly iridescent, as in Nos. 968, 969. Galena, in consequence of its lustre, is sometimes known as Lead glance. The coarsely-crystalline galena, generally considered, though sometimes erroneously, to be poor in silver, is known from its use in glazing pottery as potters' ore."f The amount of lead ore, princi- pally galena, raised in Derbyshire in 1902 was 3,555 tons. * " The Deposit at the Mill Close Lead Mine, Darley Dale, Matlock." By Cyril E. Parsons. Trans. Fed. Inst., vol. xii. (1896), p. 115. t On the Continent this ore is known as alfjuifoux a word which is derived, as Prof. Bauerman has pointed out, from the Italian archifoglio, or " large-leaved," being the name applied to it in the Levant trade. The ore is exported to Egypt as a remedy in ophthalmia and for painting the eyelids. The Arab name is kohlhe, whence it is known in parts of Spain, where it is used in potteries, as alcohol. " The Metallurgy of Lead." By John Percy, M.D., F.R.S., 1870, p. 94. 7882. L 138 MINERALS OF DERBYSHIRE. In the specimen No. 982, the smooth surface of the galena presents a natural polish, and is known as a slickenside. This polish is the result of friction due to movement in the vein, and the direction of movement is indicated by the grooving or fluting seen on the face of the stone. It is remarkable that some of the Derbyshire slickensides, on being struck with a pick, will explode with more or less violence. The molecules of the rock appear to be in a condition of severe strain, like those of a Rupert's drop, so that the slightest breach of con- tinuity at one spot, such as may be produced by a mere scratch, will disturb the unstable equilibrium and lead to disruption throughout a considerable mass. The subject of explosive slickensides has been studied by Mr. A. Strahan.* Many of the specimens in this case illustrate the characteristic associates of galena. In No. 983 the galena occurs with calcite ; in No. 984 with fluorite ; in No. 985 with barytes ; and in No. 986 with blende. The occurrence of galena with the minerals resulting from its own alteration, like cerussite and anglesite, is illustrated in the following series. Cerussite (Nos. 987 to 990). The formation of Cerussite, or carbonate of lead, from galena is illustrated by several specimens in this Case (Nos. 987 to 989), where the two minerals are intimately associated, whilst the galena shows in some cases, by its eroded surface, that it has suffered much alteration. Frequently the carbonate occurs as a white, earthy incrustation on the weathered galena near the back of a vein. Re- garded formerly, according to Farey, as a useless spar, it was either left in the mines or thrown away and buried in the hillocks. At times it has been rather extensively worked under the name of white ore or wheat stone, and a vein at Tideswell Moor has received the name of the " White Rake," in consequence of the occurrence of this mineral. The direct oxidation of galena might be expected to give rise to anglesite rather than to cerussite, since the sulphide would become converted into sulphate ; but the reaction of this sulphate with the limestone would result in the formation of a carbonate. The action of carbonated waters on galena in a limestone matrix invari- ably produces cerussite ; and hence masses of galena, more or less altered to impure white ore, or ' lead earth ' (Bleierde), are often found in ore-deposits, within reach of surface drainage. The fine prismatic crystal of cerussite, numbered 990, is dull and blackened on the surface. Such discolouration is probably due to the formation of a thin layer of black sulphide, consequent on attack by sulphuretted hydrogen. This product is often evolved from decomposing sulphides. Moreover, the sulphur compounds emitted by blasting operations in mines tend to blacken any white lead-ore in their neighbourhood. * " On Explosive Slickensides." Oeol. Mag., Dec. 3, vol. iv. (1887), p. 460. LEAD-ORES. 139 Anglesite, etc. (Nos. 991 to 994). Wherever galena has suffered oxidation, but has been shielded from the attack of carbonates, Anglesite, or sulphate of lead, may be expected to occur. Although in limestone districts it is naturally not so common as cerussite, fine crystals have occasionally been yielded by the lead mines of Derbyshire. Of these, several ex- amples are here shown (Nos. 991 to 993). The characters of the species have already been described in connection with the original occurrence in Anglesea (p. 127). It is worth noting that although galena and blende occur together in the Derbyshire mines, the products of their oxidation present marked differences. Sulphate of lead is very sparingly soluble in water whilst sulphate of zinc is freely soluble. Hence the lead com- pound remains as a fairly stable mineral, whilst the zinc salt is carried off in solution and is rarely found in a solid form. Goslarite, or sulphate of zinc, though not unknown in stalactitic forms in certain mines, may be practically ignored as a British species. Specimens of lead- ore from the refuse-heaps of an old mine near Brassington were collected by Sir H. T. de la Beche, to illustrate the alteration of galena by prolonged weathering, and were described in his Geological Observer (p. 692). Several of these specimens are exhibited in Wall-case No. 35. They show the galena encrusted with cerussite and pyromorphite that is to say, the sulphide has been more or less completely converted into carbonate and phos- phate. The brown phosphate is known as linnets, and the green as green linnets. No. 994 is an example of these alteration-products from the Brassington hillocks. The name of " Green Linnets " was given to the mine which yielded these specimens. Matlockite and Phosgenite or Cromfordite (Nos. 995 to 1006). Derbyshire has contributed to the group of plumbiferous minerals two rare and interesting species, which have been called, from their original localities, Matlockite and Cromfordite. Both minerals contain lead in the form of chloride, associated in the former with an oxide, and in the latter with a carbonate of lead. Such at least is the common interpretation of their constitution. Again, both crystallise in the tetragonal system ; but whilst the crystals of matlockite usually have a tabular habit, due to development of the basal pinacoid, those of cromfordite, though sometimes tabular, have generally a prismatic habit. With regard to the names of these two species it may be remarked that whilst matlockite is the name universally used to designate the oxychloride, the term cromfordite, proposed by Greg and Lettsom for the oxycarbonate, and locally appropriate, has given place, in most quarters, to Breithaupt's name Phosgenite,* which, notwith- standing its rather fanciful origin, has survived by right of priority. * Phil. Mag., ser. 4, vok ii. (1851), p. 120. 7882 L 2 140 MINERALS OF DERBYSHIRE. The fine series of specimens of matlockite, Nos. 995 to 1002, illustrate the typical characters of this mineral, showing the yellowish adamantine tabular crystals, in some cases slightly curved and aggregated in groups with a tendency to a globular form. The mineral is identical in chemical composition with the white pigment at one time largely prepared under the name of Pattinson's oxy- chloride of lead.* Matlockite has been found among the sublima- tion products of Vesuvius ; but its occurrence in Derbyshire suggests, of course, quite a different origin, and rather recalls the mode of formation of mendipite another oxychloride of lead already noticed in connection with the minerals of Somersetshire. The relation of matlockite and mendipite is seen by comparison of their formulae : Matlockite ... Pb C1 2 . PbO. Mendipite ... Pb C1 2 . (PbO) 2 . Phosgenite is represented by a fine suite of specimens (Nos. 1003 to 1006), including some beautiful transparent crystals, faintly yellowish in colour and adamantine in lustre. The formula of the species may be written Pb C1 2 . Pb C0 3 . It has been found naturally altered to Cerussite, a change obviously brought about by removal of the molecule of lead chloride. Phosgenite has been found in the neogenic deposits of Bourbonne-les-Bains, and in the old slags of Laurion, where the chlorine has been supplied by the sea- water. Soluble chlorides reacting with carbonate of lead, dissolved by carbonic acid, might give rise to such a chloro-carbonate as phosgenite. The artificial production of this species was effected by MM. Friedel and Sarasin, by heating a mixture of chloride and carbonate of lead with water in a closed tube at a temperature of 180. With regard, however, to the Derbyshire mineral, which was produced by the alteration of galena, there is no reason to suggest for its production an elevated temperature. It is therefore interesting to note that M. A. de Schulten has effected the synthesis of crystallised phosgenite at ordinary temperature by passing a current of carbonic acid gas through an aqueous solution of chloride of lead.f Both matlockite and phosgenite were originally found in old workings in the lead mines near Cromford, not far from Matlock. The locality given for phosgenite was the Boge Mine, in the little village of Bole Hill. The chlorine in these minerals may possibly have been derived, as suggested with regard to mendipite (p. 109), either from neighbouring saliferous rocks now removed or more pro- bably from surface-waters carrying a small proportion of chlorides. Blende (Nos. 1007 to 1010). In Derbyshire, as in so many other localities in limestone rocks, the ores of zinc occur in intimate association with those ol lead. * Percy's " Metallurgy of Lead." 1870, pp. 79, 81. t " Siir la production artificielle a la temperature ordinaire de la Phos- g3Tt9." Par M. A. de Schulten. Bull Soc. Fr. Min.> vol. xx. (1837), p. 191 LEAD AND ZINC ORES. 141 The principal zinc-ores are the sulphide and the carbonate, the latter being in most cases a secondary mineral derived from the former. Whilst the native sulphide is commonly known as zinc Uende, or simply blende, it is nowadays frequently termed by mineralogists sphalerite a name due to Haidinger, who, in the year 1845, intro- duced it as a scientific word having much the same meaning as the vulgar name " blende " ;* that is to say, it indicated the deceptive character of the mineral which had led to its occasional confusion with galena. The same idea is conveyed by the miners' terms mock ore, false lead, or black Jack. In deposits of mixed lead and zinc-ores the lead is likely to occur in the upper part and the zinc below ; and for this and other reasons the working of zinc-ore in a given district is often of comparatively recent date. Blende is less stable than galena, so that in the zone of oxidation it will be first attacked ; and moreover, the zinc sulphate by reason of its greater solubility is so much more mobile than the lead sulphate that it will tend to move downwards, where it may be reduced to a less soluble form. Some of the specimens show the blende in association with cubes of fluorspar (as No. 1008) ; and in specimen (No. 1009) it is crystal- lised with fluor in a fossil shell. The dark colour of common blende, whence the name " bkck " Jack, is due to iron, probably in the con- dition of FeS, a compound which occurs as a cubic mineral in meteorites, and is known as Troilite. The ' rosin blende " is paler. At the present time the only mine in Derbyshire raising zinc-ore is the Mill Close Mine, in Darley Dale, which yielded 538 tons of ore in 1902. Calamine, etc. (Nos. 1011 to 1018). Solutions containing zinc, such as those resulting from the altera- tion of blende, are apt, on percolation through limestone, to form carbonate of zinc, or calamine ; and since this body, unlike its isomorph, ferrous carbonate, is characterised by much stability, the metal may remain fixed in the form of carbonate. Zinciferous solutions, by slowly attacking limestone, may effect the gradual substitution of zinc for calcium, and thus give rise to metasomatic deposits of calamine. In No. 1012 crystals of Derby- shire dog-tooth spar have suffered partial alteration, and show a thin external crust of calamine. The same kind of crustal alteration has roughly affected the two bold scalenohedra in No. 1013. The next specimen, No. 1014, shows that the calcite has been partially dissolved away beneath the calamine, so that a thin shell of the zinc carbonate is separated by a solution-space from a nucleus of un- altered calcite. In No. 1015 all the calcite has disappeared, leaving nothing but a thin shell of calamine representing not only the * Sphalerite from rj (selene) the moon, the mineral must not be confounded with the "moonstone" of the jeweller, which is adularian felspar. See specimens in Horse-shoe Case, Section T. 184 MINERALS OF THE NEOZOIC STRATA. cleavage parallel to the clinopinacoid. Many of the crystals are of tabular habit, and the large lozenge-shaped face seen on several of the specimens is this plane of easy cleavage. Thin transparent cleavage- flakes, mostly of diamond shape, were formerly used to a limited extent in place of glass. The mineral may be cleaved also, though less perfectly, in two other directions. Twin crystals are common in gypsum, as seen in Nos. 1393, 1394 ; and the twinning may give rise to arrow-headed and swallow-tailed crystals. The faces are often curved, as in No. 1395, whilst in some instances the crystals become quite lenticular in shape, as in No. 1396. The specimen No. 1399 is a group of lenticular crystals from the Oldhaven beds of Reculver Cliff, in N. Kent, remarkable for having a large proportion of sand mechanically associated with the gypsum an occurrence which reminds the mineralogist of the so- called " Fontainebleau sandstone," in which calcite mixed with much sand has crystallised in rhombohedra. (See specimens in Horse- shoe Case, Section I.) Crystals of selenite, often known in brickyards as "congealed water," are common in most clays and in many shales, which are simply indurated and laminated clays. The mineral may be formed in such situations by the action of sulphuric acid or of sulphate of iron, resulting in either case from the decomposition of iron pyrites, on calcareous matter, such as that of shells. In lime- stone a similar reaction may occur. Crystals of gypsum have been formed artificially by allowing a solution of ferrous sulphate, in con- tact with air, to react on chalk, the gypsum being here accompanied by the formation of ferric hydrate. Such an association, brought about naturally, is illustrated by a specimen from Brighton in the Horse-shoe Case. Examples of selenite are exhibited not only from the Keuper marl and from the Kimeridge clay, as mentioned above, but also from the Woolwich and Beading clays, as in No. 1398, presented by Dr. G. Abbott. The late Professor P. M. Duncan, in calling attention to the occurrence of moulds in certain Eocene clays, indicating the former presence of selenite, explained the removal of the mineral by assuming that deoxidation had been effected by means of de- composing organic matter, whereby the sulphate had been reduced to sulphide of calcium, which is an extremely unstable substance.* Professor Lacroix has remarked that if calcium sulphide be acted on by a solution of acid carbonate of iron, the products of the reaction may be pyrites and calcite.f Gypsum may be readily removed from one spot and carried to another by mere solution in water. According to Mr. G. K. Cameron, one part of gypsum is soluble in 372 parts of pure water at 26C. It is well known that * " On the spaces formerly occupied by Selenite in the Lower Eocene Clays of the London Basin ; with Remarks on the Origin and Disappearance of the Mineral." Quart. Journ. Gecl 8oc., vol. xxii. (1866), p. 12. t " Le Gypse de Paris." Nouv. ArcUv. Mus. d'Hist. Nat., 3 ser.. vol. ix, (1897) p., 201. , ETC. 185 Waters draining gypseous rocks, like those of the Trent, contain much sulphate of lime in solution; and such permanently hard waters, valued for brewing as at Burton, are said to be " selenitic." The decomposition of gypsum gives rise in some cases to the elimination of Native Sulphur, as shown in a specimen in the Hall, where sulphur is seen in a mass of gypsum from Newark. Mr. R. P. Cafferata has remarked that in the course of twenty-four hours after quarrying the " Blue Rock " free sulphur appears in consider- able quantity.* The reduction is generally effected by organic matter, probably through the agency of sulphur bacteria. f Gypsum is readily converted into calcite, even in the cold, by the action of a solution of certain carbonates. A crystal of gypsum which has undergone this change will be found in the interesting group of artificial pseudomorphs, prepared and presented many years ago by Dr. H. C. Sorby, F.R.S., and exhibited in Wall Case 35. According to official statistics the amount of gypsum raised in England in 1902 was 224,669 tons. This amount was yielded by the following counties, the first- named being the largest producer, and the others in regular sequence yielding less and less : Nottingham, Stafford, Cumberland, Sussex, Derby, Yorks, Westmorland and Somerset. Whilst most of the gypsum comes from the Keuper marl, it has been pointed out by Mr. J. G-. Goodchild that the gypsum of Edenside is referable to a lower horizon, being on or near the Mag- nesian Limestone. J Widely different in geological age, from the Permo-triassic gypsum, is the gypsum of Sussex, of which a sample is here shown (No. 1385). This mineral was discovered in the famous sub-Wealden boring at Mountfield, near Netherfield, not far from Battle, and is believed to be of Purbeck age. Much gypsum occurs in the Isle of Purbeck, and the mineral was formerly worked in the lower Purbeck beds of Durlston Bay. Anhydrite (No. 1400.) Whilst gypsum contains two molecules of water of crystallisation, the mineral called Anhydrite is a sulphate of calcium destitute of water, whence indeed its name. Unlike gypsum, anhydrite crystal- lises in the orthorhombic system, but crj^stals are rare, at least in this country. Anhydrite is harder and denser than gypsum, and admits of being polished like a piece of marble. It frequently presents a pale blue colour, as seen in No. 1400. Anhydrite readily passes into gypsum, with an increment of volume of about 60 per cent., and conversely gypsum may become converted into anhydrite. It has been suggested that much of the gypsum in * Cited by Mr. Metcalfe, op. cit. t Prof. Lacroix : " Mineralogie de la France," vol. ii (1897), p. 370. j " Some Observations upon the Natural History of Gypsum," Proc. Geol. Assoc., vol. x (1888), p. 425. "The Geology of the Isle of Purbeck." By Aubrey Strahan, M.A. Mem. Geol. Surv., 1898, p. 237 7882 O 386 MINERALS otf THE NEOZOIC STRATA, this country may have been derived from the alteration of anhydrite. In Nottinghamshire anhydrite occurs in the heart of certain masses of gypsum, and this kernel seems to represent the original mineral. It was formerly supposed that the production of anhydrite required a moderately elevated temperature, but it is now known that the mineral may be deposited at normal temperature, especially from saline solutions. The researches of Professor van't Hoff have shown that " solutions containing, calcium sulphate which have a tension lower than 17.2 m.m. at 25 deposit it as anhydrite. This is the case in the deposition from sea- water."* Celestite (Nos. 1401, 1402.) Native sulphate of strontium, like sulphate of calcium, is a mineral not infrequently found in the New Red Sandstone. Its occurrence in the Bristol district has already been described (p. 113) and some fine examples are exhibited in Case VII., but a specimen is also placed here, in order to illustrate with some approach to fulness the mineral products of the Trias (No. 1401). Celestite, or celestine, is frequently found in association with gyp- sum, as illustrated by No. 1402 and by specimens in Section G of the Horse-shoe Case. Even when not detected by the naked eye the presence of celestite in gypsum may sometimes be revealed by the microscope. Natural waters, especially in the New Ked Sandstone, often contain an appreciable quantity of sulphate of strontium. Its occurrence in the water of the famous dropping well of Knares- boroughj and in the Bristol waters has already been referred to (p. 114). Celestite is found in many sedimentary strata, though by no means so common a mineral as barytes. A specimen in the Case illustrating Fossilisation is interesting as showing celestite finely crystallised in the chambers of an ammonite from the Lias of Adderley in Shropshire. Collectors of minerals are familiar with the flints of Meudon, near Paris, containing crystals of celestite, of which a specimen will be found in the Horse-shoe Case, but the mineral is not known to occur in the chalk-flints of this country. Barytes (Nos. 1403 to 1406). r Barium is an element of much wider diffusion than the kindred element strontium, occurring as it does in a large number of rocks, both sedimentary and eruptive, and in many natural waters.^ Attention has been called in recent years to the occurrence of barium in many of the Triassic sandstones. Mr. A. Strahan, in describing the rock of Beeston Castle in Cheshire, which is Keuper sandstone, * Journ. Chem. Soc., vol. Ixxxii (1902), Part ii., p. 138 : abstract of paper by van't Hoff and Weigert in Sitzungsber. K. Akad. Wiss. Berlin, 1901. t Proc. Yorkshire Qeol. and Pdyt. Soc., new ser., vol. xiii., p. 135, $ See Delkeskamp's paper cited on p. 169. BARYTES, 187 alluded to the veins of Barytes in the joints of the rock, and to the occurrence of the mineral in the rock itself, as well as in the breccias of the Peckforton ! Hills.* Prof. Clowes found barium sulphate in the Bunter sandstone of the so-called " Hemlock Stone," near Nottingham, where it occurs as a cementing medium uniting the siliceous grains, t Prof. W. W. Watts has described the occurrence of barytes under similar conditions in the Lower Keuper sandstone of Peakstones Kock, near Alton, in Staffordshire.:]: So again, the occurrence of barytes in both Bunter and Keuper sand- stone at Bidston, in Cheshire, has been recorded by Mr. C. C. Moore and Mr. J. Lomas. It should be noted too that Dr. H. T. Brown has found barium existing in the form of carbonate in some of the Triassic sandstones in Cheshire, whilst Professor Clowes has sug- gested that the reaction of this soluble compound with certain sulphates may have led to the formation of barytes in the rocks. Gypsum is not uncommon in the sandstones of Nottinghamshire. In mineral waters barium frequently exists in the form of chloride. An exceptionally large proportion was found by Prof. E. T. Thorpe in the waters of Harrogate, the water of the Montpellier Strong Sulphur Well yielding an amount of barium equivalent to 9'5 grains of chloride per gallon. || It is notable, too, that the proportion of barium in the Harrogate water seems to be increasing. Barium chloride also occurs, to the extent of more than 6 grains per gallon in the waters of Llangammarch Wells in Breconshire. As far back as 1847 Dr. Richardson detected barium in the waters of Walker Colliery, near Newcastle, and a large mass of barytes was found in Felling Colliery.^ Prof. Clowes has called atten- tion to the large proportion of barium in the waters of certain col- lieries in Durham, which is the cause of a deposit forming in the pipes and water boxes connected with the mining pumps. In some cases the deposit contains as much as 90 per cent, of sulphate of barium, and it is an interesting fact that sulphate of strontium is also present in the deposit, in some cases to the extent of 8 per cent. Prof. Bedson found barium chloride in the colliery waters, and, as Prof Clowes remarks, this solution would give rise to a precipitate of barytes by reaction with ferrous sulphate, or with free sulphuric acid, which might readily result from the decomposition of pyrites. In Case VIII. will be found a nodule of clay ironstone enclosing barytes, from the Whitehaven coal-field (No. 1091), and it is known that barytes likewise occurs in the Coal- brook Dale ironstone. * " The Geology of the Neighbourhood of Chester." M em. Geol. Surv. Expl. Quart. Sheet 80, S.W. 1882. t " Barium Sulphate as a Cement in Sandstone." Proc. Eoy. Soc., vol. xlvi. (1890), p. 363. J Rep. Brit. Assoc. for 1894, p. 665. Geol. Mag., [iv J vol. i. (1894), p. 520. Proc. Liverpool Geol. Soc., vol. viii. (1900), p. 241. || Journ. Chem. Soc., vol. xxxix. (1881), p. 510. Tf " On Minerals and Salts found in Coal-pits.' 1 By R. Calvert Clapham and John Daglish. Trans. N. Eng. Inst. Min. Eng., vol. xiii. (1864), p. 219. 7882. O 2 188 MINERALS Otf THE NEOZOIC STRATA. In the Triassic sandstone of Elgin barytes has been found, and here Dr. W. Mackie regards it as a precipitate from an inland sheet of salt water.* Commander A. Carpenter dredged off Colombo, in the Indian Ocean, in 675 fathoms of water, small nodules con- taining 75 per cent, of barium sulphate.f It is worth noting that certain crystals of barytes from Teplitz, described by Dr. F. Becke, appear to have been formed by pre- cipitation from the hot springs, where, though the crystals reach a length of five centimetres, the proportion of barium in the water is so small as to elude analytical determination. { The finest specimens of barytes yielded by the Neozoic strata of Britain are the large yellow crystals formerly found rather abun- dantly, though now rare, in the pits worked for fuller's earth in the Lower Greensand of Nutfield, near Redhill, in Surrey (Nos. 1403- 1404). As far back as 1819 this occurrence was described by Thomas Webster, who speaks of masses of barytes found here weigh- ing a hundredweight. The crystals, which though large are rarely terminated, were studied by Prof. Chapman, of University College, London, who described the mineral as barytine.\\ Some excellent examples of the Nutfield barytes are here shown, and others will be found in the Horse-shoe Case. The crystals, rather like sugar-candy in colour, are associated with crystallised quartz, sometimes slightly amethystine in tint. Iron-pyrites also occurs with the barytes, and a little carbonate of copper has occasionally been found. The presence of barytes was not favourably viewed by those who worked the fuller's earth. Very different from the Nutfield mineral is the barytes occasion- ally found in the septaria of the London clay, especially in the Isle of Sheppey. Here it occurs in slender opaque white crystals, arranged in radiating forms or in stellate groups, and rather effec- tively disposed on the yellow calcite which has crystallised in the contraction-cracks of the nodules, and was formerly called the " waxen vein." This occurrence of barytes was recognised by such early observers as Dr. Grew and Sir John Hill, who described the mineral under the name of lepastrum, and appear to have regarded it as gypsum. Some of the specimens here shown (Nos. 1405, 1406) are said to have come from Whitstable Bay ; and according to Sowerby the barytes was also found under similar conditions at Southend, at Sydenham, and at Highgate.^J From the difficulty of dissolving sulphate of barium, it might be supposed that the mineral would be extremely immobile, not easily removed from one place and deposited in another. According * Rep. Brit. Assoc., Glasgow, 1900, p. 649. f Journ. Asiatic Soc. Bengal, vol. Ivi. (1887), p. 209. Quoted in " Report of the Challenger." | Tschermak's Min. Hit., vol. v. (1888), p. 82. " On the Geognostical Situation of the Reygate Stone and of the Fuller's Earth at Nutfield." Trans. Geol. Soc., vol. v. (1819), p. 326. || " Mineralogical Notes," Phil. Mag. [4], vol. iii. (1852), p. 144. 1[ " British Mineralogy," vol. iii., p. 199 ; vol. v., p. 39. COPPER-ORES. 189 to Holleman, one part of the salt requires for solution 429,700 parts of water at 18.4 C.* Referring to the waters of Bath, the Hon. R. J. Strutt observes that " Barium sulphate requires half a million times its weight of water to dissolve it ; radium sulphate perhaps several hundred million times its own weight, "f Barytes not infrequently contains a small proportion of the sulphates of strontium and calcium. With celestite the barytes is clearly isomorphous, but such relationship can hardly be extended to the corresponding calcium salt, for though anhydrite crystallises like the others, in the orthorhombic system, it yet differs markedly in form and in cleavage. Copper-Ores, etc. (Not. 1407 to 1408). Copper is rather widely distributed through many sedimentary rocks, but is rarely present in large proportion, except in rocks of the New Red Sandstone period. Dieulafait referred the origin of the copper to deposition from sea-water. In the waters of the Mediterranean, he found copper to the extent of 0*01 gramme per cubic metre ; and he showed that the black mud left by evaporation of sea-water, whether in natural or in artificial basins, invariably contained this metal. Perhaps the most important copper-bearing rock of sedimentary origin is the famous Kupferschiefer or copper-shale, of Germany, which though only a thin stratum containing but 2 or 3 per cent, of copper, has nevertheless been worked for at least seven centuries, and still yields a large output of copper. The black shale is rich in fossil fishes, like Palceoniscus, and it was suggested by Groddeck that the discharge of cupriferous springs into the basin in which the mud was in course of deposition must have destroyed the fish-life, whilst the decaying organic matter would lead to the forma- tion of sulphides. According to Dieulafait the copper might be derived simply from sea-water, by evaporation in a closed basin ; the gypsum which would be deposited in the lagoon might suffer reduction by decomposing organic bodies, with the formation of sulphides, which would precipitate the copper, in a sulphuretted form. It is notable, however, that the marl-slate of Durham, which is a Permian deposit at the base of the Magnesian Limestone, on precisely the same horizon as the German copper-shale and closely related to it palseontologically, appears to be quite destitute of copper .f The copper-bearing strata of this country are almost exclusively of Triassic age. Reference has already been made to the occurrence of copper-ores in the Dolomitic Conglomerate of the West of * Zeit. Phys. Chem., vol. xii., p. 125. f Proc. Roy. Soc., vol. Ixxiii. (1904), p. 195. See Prof. Lebour's remarks in Trans. Inst Mining Eng,, vol. xxiv, (1904), p. 390. 190 MINERALS OF THE NEOZOIC STRATA. England (p. 112), but the most noteworthy examples of cupriferous strata are to be found in Cheshire, where sandstones and conglo- merates, formerly regarded as Keuper but now referred by some authorities to the Bunter, have been systematically worked for copper at Alderley Edge and at Mottram St. Andrews, near Maccles- field, the beds being there repeated by a fault. The bright colour of the copper carbonates in these rocks propably attracted attention at a very early period ; and the rude stone hammers found by Prof. Boyd Dawkins, Dr. Sainter, Mr. Boeder, and others, point to work- ings even in prehistoric times.* At Mottram St. Andrews the copper was worked chiefly in a hard quartzose conglomerate, which contained an average of about 5 per cent, of copper-ore. At Alderley Edge, about a mile to the south- west, the ores were mostly found in three beds of sandstone, where the proportion of copper averaged about 1*4 per cent, of the work- able parts of the stone.f The grains of quartz in the sandstone were invested by a coating of copper carbonate. The specimen here exhibited (No. 1407) is a quartzose conglomerate, with malachite and azurite. The sandstones are variously coloured by several mineral pigments yellow and brown by iron oxides, blue and green by copper carbonates, and black by manganese oxide and earthy cobalt-ore. Although these cupriferous sandstones are no longer worked, they were at one time the object of rather extensive mining operations, and the ore was profitably treated by a wet process. The coarsely ground sandstone was digested with dilute hydrochloric acid, whereby the copper was dissolved out, and from this solution of the chloride the metal was precipitated by scrap-iron. The " cement copper " con- tained about 80 per cent, of metallic copper. The cobalt, which occurred to a small extent in the sandstone in the form of asbolan, was recovered by adding milk of lime to the liquor after removal of the copper. The precipitate thus obtained carried the cobalt, with a little arsenic. It is notable that copper is also accompained by cobalt in many other localities, as at Bieber in Hesse. Some of the Chesire sandstones contained also lead ore, chiefly in the form of cerussite, though they likewise yielded subordinately galena, pyromorphite and vanadinite. A sample of Alderley Edge sandstone, with lead-ore is here exhibited as No. 1408. Attempts to treat the plumbiferous sandstones were not commercially successful. These stratified lead-ores rather remind the miner of the sandstones which are extensively worked near Mechernich and Commern, in Rhenish Prussia, where the Bunter sandstone contains nodules, or Knotten, of galena, associated with cerussite and locally with a little copper carbonate. * " Prehistoric and subsequent Mining at Alderley Edge," by Charles Boeder. Trans. Lancashire and Cheshire Antiq. Soc., vol. xix. (1902). f M em. Geol. Swv. Prof. Hull's Memoir on Geology of Stockport. Also Mr. Greenwell in Proc. S. Wales Inst. Min. Eng., vol. iv. (1866), p. 44. IRON-ORES. 191 SirH. E. Roscoe many years ago described a vanadate of lead and copper, which was found at Alderley Edge and at Mottram St. Andrews, to which he gave the name of Mottramite. It formed on the sandstone a thin incrustation, in some cases black and velvety, with crystalline structure, and in other cases compact and of purplish brown colour.* It may not be without interest to recall the fact that other vana- dates are elsewhere present with Permian copper-ores ; witness the occurrence of volborthite, a vanadate of copper, in the cupriferous sandstone of Perm in Russia. Iron-ores (Nos. 1409 to U19). Of the many iron-ores found in the Secondary strata of Britain the most famous is the ore of the Cleveland district in the North- east of Yorkshire (No. 1409). The Cleveland ore occurs in the Middle Lias, or Marlstone, where it forms several bands, the most important seam being nearly twenty feet in thickness. Though not everywhere uniform in character, the ore when freshly raised is typically a light bluish-green oolitic rock, containing about 30 to 32 per cent, of iron, chiefly in the form of carbonate.f The greenish colour is referred to the presence of glauconite, or some other silicate of iron, whilst the bluish tint may be due to a phosphate like vivianite. Phosphorus is always present, though in variable proportion, the average being about 1*5 per cent. As the ore is highly fossiliferous the origin of the phosphorus is readily traced. Indeed the two principal beds of ore are known, from their characteristic fossils, as the Pecten Seam and the Avicula Seam. Traces of various extraneous metals, like zinc, nickel, and cobalt, are commonly present in the Cleveland ore ; and Mr. A. Dick, in the course of an analysis found in the insoluble residue, microscopic crystals of Anatase, associated with quartz. { Titanium oxide, in the form of anatase and of rutile, has been shown by several recent observers to be widely distributed in the sedimen- tary rocks of this country. The presence of zinc in the Cleveland ore offers no difficulty, inasmuch as the frequent association of * " On two new Vanadium Minerals." Proc. Roy. Soc., vol. xxv. (1876), p. III. The other mineral referred to in the title of the paper is the vanadium- mica called Roscoelite (p. 109). t For full description of the Cleveland ore, see Mems. Geol. Surv. " The Geology of North Cleveland," by George Barrow, 1885, p. 80. " The Jurassic Rocks of Britain, vol. i., Yorkshire." by C. Fox-Strangways, 1892, p. 433. J " The Iron-ores of Great Britain," (Mem. Geol. Surv.), part i., p. 95. See Mr. Scrivener's paper on " Anatase in the Trias of the Midlands of England," in Min. Mag., vol. xiii. (1903), p. 348, where references are given to the work of Dr. J. H. H. Teall, Mr. Maynard Hutchings, Mr. A. Dick, and Mr. H. H. Thomas. In a paper on the " Distribution of Titanic Oxide upon the Face of the Earth" (Am. Journ. Sc. [3], vol. xlii., 1891, p. 491), Prof. F. P. Dunnington records his examination of " black garden soil from Kensington," which yielded 0-21 per cent, of titanic oxide. The common occurrence of titanium in iron-ores explains the origin of the cyano-nitride of titanium, which is occasionally found in small copper-like cubes in the " bear " of blast furnaces. 192 MINERALS OF THE NEOZOIC STRATA. zinc-blende with carbonate of iron is well known, and is very marked in the Lias.* According to Professor Hartley the Cleveland ore, like many other ores of iron, contains gallium. From the microscopic structure of the Cleveland iron-ore, Dr. Sorby showed, many years ago, that it had probably been originally an oolitic limestone, which became altered by the action of a solution of bicarbonate of iron, derived perhaps from the inters tratified shales which contained oxide of iron and organic matter.f In some of the fossil shells associated with the ore, the carbonate of lime is partially replaced by ferrous carbonate. The Cleveland ore is raised at the present time (1904) to the extent of about 5,600,000 tons per annum, an amount which represents rather more than two-fifths of the total output of iron ore in the United Kingdom. The iron- ores of the Middle Lias have been worked not only in Yorkshire, but also in Lincolnshire, Leicestershire, and Oxfordshire. The ore of Frodingham in N. W. Lincolnshire is refer- able, however, to the Lower Lias.f At Kosedale Abbey, in Yorkshire, there occurs an oolitic ironstone of nearly black colour, peculiar in being magnetic and polar. This magnetic iron-ore represented by No. 1410, occurs in the Dogger series, belonging to the Inferior Oolite. Crystals of magnetite, as Prof. Lacroix has pointed out, occur in some of the oolitic brown iron-ores of France. The formation of magnetite in the wet way possibly receives illustration from an observation of F. M. Stapff, who found that the rust on nails from ancient mines in Spain, believed to be 2,000 years old, consisted of a mixture of limonite and magnet ite. Prof. Bauerman has called attention to the similarity of the Rosedale ore to the mineral worked on the Continent under the name of Chamoisite a pisolitic magnetic ore of Jurassic age.H A vast quantity of siliceous brown iron ore is raised annually from the Oolites of this country.^ The Northamptonshire ore (No. 1411) largely developed in the Northampton sand, forming part of the Inferior Oolite, presents the aspect of a rusty brown granular mass, composed of iron hydroxide and quartz. At considerable depths, however, the unaltered ore is a bluish or greenish grey substance, * See for instance, " The Yorkshire Lias," by Ralph Tate and J. F. Blake, 1876, p. 163. Also Mr. C. Fox -Strang ways' Geol. Surv. Mem. on the Jurassic Rocks of Britain, vol. i., p. 473. t " Origin of the Cleveland Ironstone." Proc. Geol. Polytech. Soc. West Riding, vol. iii. (1856-7), p. 460. Also : Quart. Journ. Oeol Soc., 1879. J See paper by the late Rev. J. E. Cross in Quart. Journ. Geol. Soc., vol. xxxi. (1875), p. 115. Also, Mem. Geol. Surv. " The Jurassic Rocks," vol. iii. By Horace B. Woodward, 1893., p. 300. Jahrb. f. Min., 1895, part i., p. 69. [ || " A Treatise on the Metallurgy of Iron, 6 ed., 1890, p. 87. T[ It may bo noted that the Jurassic brown ores of Luxemburg and Lorraine are known as m,inette a diminutive of mine, or ore. Iron -ore is often called in this country " mine," and the diminutive would indicate a lean or poor ore. Minette is used also as the name of an igneous rock. IRON-ORES. 193 composed mainly of impure ferrous carbonate. The bluish colour is regarded by Professor Judd, as probably due to the diffusion of a small proportion of iron sulphide throughout the mass, whilst the greenish tint may be referable to the presence of ferrous phosphate rather than to a silicate.* The brown iron ore of Westbury, in Wiltshire (No. 1413), and that of Abbotsbury, in Dorsetshire, are referable to the Corallian strata. At a slightly higher horizon is the brown iron ore, which was found in the Dover boring. This ore forms a band 12 feet in thickness, described by Prof. Boyd Dawkins as composed of grains of hydrated oxide of iron in a base consisting partly of carbonate of lime and partly of carbonate of iron.f The ore of Seend, near Devizes, in Wiltshire, occurs in the Lower Greensand ; indeed much of this Greensand consists of iron- shot sands, and the proportion of iron occasionally rises sufficiently high to constitute a siliceous iron-ore. Examples of all the Jurassic and Cretaceous iron-ores are shown in the Wall cases 47 and 49, and others will be found in the Petro graphical Collection. Ironstone was formerly worked on rather a large scale in the W ealden beds, principally in the Wadhurst clay, but also to a limited extent in the Ashdown sands. The ore (No. 1414) is a kind of clay ironstone, containing as much as 35 per cent, of metallic iron. It was this ore that formed the raw material of the iron industry which flourished for ages in the Weald of Sussex and Kent, and was not extinguished until the early years of the nineteenth century. Many of the "bell pits" from which the ore was raised still exist, though now generally filled with water. The ore was smelted with charcoal as a fuel the charcoal being mainly derived from the oak forests on the Weald clay and with the Pdudina (Viviparux) limestone, or Sussex marble, as a flux. Cinder-heaps, or accumula- tions of old iron-slags, still exist in the Weald. J In the Tertiary strata nodules of clay ironstone have occasionally been worked, as at Hengistbury Head in Dorsetshire, where the ore occurs in the Barton beds. The bog ores show the formation of iron- ore in progress at the present day, and may throw light upon the origin of some of the brown iron-ores of the sedimentary rocks. Mr. Hudleston has called attention to the fact that iron in rocks is rendered locomotive by means of carbonic acid, a soluble acid carbonate being formed, and is fixed by means of oxygen, the solution of bicarbonate on exposure to air depositing the hydroxide as a kind of bog ore. . *Mem. Geol. Surv. " Geology of Rutland," 1875. By John W. Judd. p. 110. " Jurassic Rocks." vol. iv. By Horace B. Woodward, p. 493. t Trans. Manch. Geol. Soc., vol. xxii. (1895), p. 501. J Mem. Geol. Surv. " The Geology of the Weald." By William Topley 1875, p. 329. " On the Geological History of Iron-ores." Proc. Geol. Assoc., vol. xi., (1889), p. 1C4. 194 MINERALS OF THE NEOZOIC STRATA. Organic agencies probably play a great part in the formation of deposits of bog iron-ore. The Rev. Dr. A. Irving has called attention to the importance of organic acids in the solution, the transport and the deposition of iron-ores. * It is known, too, that ferrous salts may be oxidised to the ferric state, without exposure to air, by the aid of ferro-bacteria. On the other hand, organic action may reduce the ferric hydroxide to the ferrous condition, and then, by means of carbonated water, a soluble bicarbonate may be formed. Kindler observed, as far back as 1835, that where pine trees were planted in sand-hills, the iron- shot sands became rapidly decolourised in the neighbourhood of the decaying roots. Ferric hydrate has great agglutinating power, and masses of sand and gravel cemented by deposits of this substance are very common where chalybeate waters percolate through beds of loose material, forming what is known as " pan" By the filtration of meteoric water through ferruginous sands curious concretionary forms may be produced tubular, globular, box-like, or quite irregular and cap- ricious in shape (No. 1415). Some of the specimens from the Lower Greensand of Leighton Buzzard (Nos. 1416, 1417) look like rusty cannon balls, but they are often mere shells, and one of them broken open here displays the hollow interior. The nodules iray enclose sand, or other substances, which rattle when the nodule is shaken. Such concretions were formerly called Eagle stones a name applied also to other hollow stones, such as chalk flints, with loose matter in the interior. The most extraordinary virtues were formerly attributed to these nodules. t No. 1418 is an old specimen of an "eagle stone," or Mtites, mounted in silver, as an amulet, but this may not be British. That such ferruginous concretions may be of comparatively recent origin is shown by the discovery in Dordogne, some years ago, of what was described as a geode of hydrate of iron containing 200 silver coins of the sixteenth or seven- teenth century.J Limonite, or brown iron ore, occurs not infrequently in stalactitic forms, which, when broken transversely, show a radial structure, the fibres being arranged in a direction normal to the axis of the stalac- tite. The surface is often lustrous, and this is specially notable in those varieties which contain manganese. Most bog iron- ore contains manganese in greater or less proportion. E xamples of the rapid formation of stalactitic limonite are often to be observed in the deserted levels of old mines. Thus, Mr. Postlethwaite records a case in which the Woodend Mine, near Threlkeld, was re-opened after having been closed for thirteen years, and stalactitic and other * " Organic Matter as a Geological Agent." Proc. Geol. Assoc., vol. xii. (1892), p. 227. See also on the Humus Acids, Prof. Julien, in Proc. Am. Assoc. Adv. Sc., vol. xxviii. (1879), p. 311. f " A Lapidary : or thb History of Precious Stones." By Thomas NicoK Cambridge, 1652, p. 148. " The Natural History, Ancient and Modern, of Precious Stones and Gems.'* Bj C. W. Kirg, M.A., 1865, p. 49. J M. Marrot in Butt. Soc. Geol. Fr. t ser. ii., vol. iii. (1846), p. 527. GLAUCONITE. 195 deposits of limonite filled up more than half the width of the level.* The recent formation of stalactitic limonite is illustrated by No. 1419 a specimen from a shaft in the camp at Dolbury, near Churchill in Somersetshire. It should be observed that certain kinds of brown iron- ore, bog- ore and ochre contain a larger proportion of water than exists in true limonite, and they should consequently be referred mineralogically to the species called Limnite or xanthosiderite. The term Stilpno- siderite is sometimes applied to limonite which presents a pitchy black surface, generally connected, as remarked above, with the presence of manganese. The surface of bog iron-ore often appears scoriaceous, and may present a brilliant iridescence. Glauconite (No. 1420). Many sedimentary rocks, especially sandstones, are speckled with dark green grains of the mineral called Glauconite. This is essentially a silicate of iron and potassium, but presents such a variability of composition as to suggest that it is a mixture rather than a true species. The specimen No. 1420, representing the green colouring matter of certain beds of Lower Greensand at Compton Bay in the Isle of Wight, was examined microscopically by Dr. Teall and analysed by Mr. Hort Player, who found that it yielded 9 6 per cent, of alumina.")" The grains of glauconite are usually the internal casts of the chambers of foraminifera, or are otherwise connected with organic structures. The mineral may have been derived from the alteration of pyrites or of certain ferro-magnesian silicates. By meteoric influences it may become converted into ferric hydrate, and hence many sandstones which are green where unexposed become rusty at the outcrop. It is noteworthy that the green sands and muds found by the <; Challenger " in shallow water, along Continental shores, are cha- racterised by the presence, more or less abundantly, of glauconitic grains and casts, associated with green amorphous matter, probably, at least in part, of organic nature. Glauconite is also present, though in smaller proportion, in the blue muds. It is most abundant near the " mud line" surrounding Continental shores, that is, at about the lower limit of the action of waves, tides and currents. J With regard to the origin of the glauconite, it has been suggested that the mud which gained access to the interior of a shell or test might contain iron sulphide which became oxidised, and the sulphuric acid resulting from this alteration would form by acting on the clay aluminium sulphate with elimination of colloidal silica, which in a nascent state might combine with the oxide of iron in the mud. As * " Mineral Springs near Keswick," Trans. Cumberland and West. Assoc., No. 11. t M em. Geol Surv. " Geology of the Isle of Wight." 2nd ed., 1889, p. 255. % " Challenger Report, " Deep Sea Deposits." 1891. p. 378. 196 MINERALS OF THE NEOZOIC STRATA. to the potash, it seems to have been derived from the sea-water itself, and probably owed its original source to the orthoclase and mica of the detrital matter.* Pyrite (Nos. 1421 to 1424). Whilst certain rocks of subaqueous formation present a greenish colour which they owe to disseminated grains of glauconite, other sedimentary rocks especially certain clays like the gault are characterised by a dull bluish colour which has been referred to the presence of finely divided iron-pyrites.f In most eruptive rocks, Pyrite may be regarded as an original constituent, but in other rocks it occurs as a secondary product, formed generally by the alteration of various ferro-magnesian minerals. In sedimentary strata the pyrites often owes its immediate origin to the reduction of a solution of ferrous sulphate, but this salt itself usually results from the oxidation of pyrites, so that the changes follow in a cycle. The reduction of the sulphate of iron by organic matter explains the common occurrence of pyrites in fossil shells, lignite and other organic structures. Instances of the recent forma- tion of pyrites by decomposing organic matter are very familiar, one of the best being the case recorded by Pepys in which it resulted from the decayed bodies of mice which had fallen into a vessel con- taining a solution of ferrous sulphate. J Iron existing in solution as a carbonate, in water containing car- bonic acid, may be converted into pyrites if sulphates and certain deoxidising agents be present. Thus, sulphate of lime in natural waters may be reduced by organic agencies, and the resulting sulphide, acting on the iron carbonate, may give rise to sulphide of iron. In other cases the sulphur may be supplied from organic sources. In the Percy Collection in the Victoria and Albert Museum there is a specimen (No. 3697) showing iron-pyrites in a log of wood from the yacht " Osborne/' which had lain for a considerable fine in a pond at Portsmouth that received the discharge of two drain*. Pyrite is one of the commonest minerals in the Neozoic strata, occurring sometimes in cubic crystals, often in the form of nodules, and very frequently in disseminated grains (Nos. 1421, 1422). By early writers like Henckel, the German pyritologist, the crystallised * On Glauconite see also von Giirubel's paper, " Ueber die Natur und Bil- dungsweise des Glaukonits." Sitzungsber. Akad. Munchen, vol. xvi. (1886). Math.-Phys. Kl., p. 417. f Ebslmen, for instance, referred the bluish tint of certain Oolitic rocks to finely-disseminated pyrites (Comptes rendus, 22 Dec., 1851 ; Butt. Soc. Geol. Fr. [2], vol. ix., pp. 213, 221). It should, however, be added that Mr. Maw doubted the pigmental effect of pyrites. See his paper " On the disposition of Iron in Variegated Strata," Quart. Journ. Geol. Soc., vol. xxiv. (1868), p. 351. J " Notice respecting the Decomposition of Sulphate of Iron by Animal Matter." By W. H. Pepys. Trans. Geol. Soc., vol. i. (1811), p. 399. Catalogue of the Percy Collection (1892), p. 433. 197 pyrites was called " marcasite," or some variant of that word* ; but the practice of modern mineralogists is to apply the term marcasite to the orthorhombic species of iron disulphide, and to restrict the name pyrite to the cubic species. The common term " iron-pyrites " is often loosely used, in a general sense, to include both modifica- tions of the mineral a practice not without convenience, inas- much as it is sometimes difficult, in the absence of crystalline form, to determine to which species a given specimen belongs. It is true the colour of marcasite is paler than that of pyrites, but the colour is frequently deepened and disguised by tarnish. Density is said to offer a criterion. According to Prof. Julien, who has made a special study of pyrites, the specific gravity of normal marcasite is very near 4 8, whilst that of pure pyrite is approximately 5 01 ; but the density is subject to much variation, since the pyrite may be associated with marcasite in a state of intimate mechanical mixture, forming what has been called " marcasitic pyrite. "f Some doubt, however, has been thrown upon this observation by Mr. H. N. Stokes. Whilst some kinds of pyrites are very stable, others are extremely prone to decomposition. Two kinds of alteration are recognised. In one case, sometimes called the hepatic change, a slow oxidation occurs, whereby the pyrite becomes externally altered to limonite, with perfect preservation of form. Examples of this limonitisation have already been noticed in connection with such specimens as No. 428 (p. 61), and other pseudomorphs of brown iron oxide after pyrite are shown here (No. 1423). Such an alteration may be brought about either by the direct action of water containing oxygen or indirectly by conversion first into a carbonate and subsequently to hydroxide. In the other kind of change, sometimes distinguished as the saline, the sulphide is oxidised to ferrous sulphate, known as a mineral under the name of melanterite, with elimination of free sulphuric acid. The melanterit? itself may then suffer decomposition, forming basic ferric sulphates, like copiapite and apatdite^, with further production of sulphuric acid. It has been said that vitriolisation is more common with marcasite than with normal pyrite ; and where pyrite suffers such a change there is probably some admixture with marcasite. In some of the pyritised fruits of the London clay of Sheppey examined by Julien, the presence of distinct octahedra showed the existence of true pyrite, but it was probably accompanied by marcasite. The so-called ' marcasite ' jewellery of the eighteenth century was invariably true pyrite, the brilliant polished surface of the mineral * " Pyritologia ; or a History of the Pyrites, the Principal Body in the Mineral Kingdom." Translated from the German. London : 1757. p. 14. f " On the Variation of Decomposition of the Iron Pyrites, its Cause and its Relation to Density." By Alexis A. Julien. Ann. N. Y. Acad., 8c., vol. iv. (1888). "Sur les produits de decomposition des pyrites, &c." Par M. A. Lacroix. Bull. Soc. Fr. Min., vol. xx. (1897), p. 288. " The microscopical structure of the Iron Pyrites." Journ. N. York Micro. Soc., May 7, 1886. 198 MINERALS OF THE NEOZOIC STRATA. being remarkably stable. A string of crystals of pyrite, believed to be from a British locality, is here shown (No. 1424). Such orna- ments, being formerly regarded as possessing medicinal virtue, were known as " Health stones " (Gesundheitsteine) and it was held that as the wearer sickened, so the stone tarnished. Marcasite (Nos. 1425, 1426). Since Haidinger in 1845 applied the name Marcasite to the orthorhombic species of iron disulphide and restricted the term pyrite to its cubic isomer, as previously explained, the names have been generally used by mineralogists in this sense. The origin of the word marcasite, usually attributed to an Arab source, has been the subject of much learned discussion.* Some of the best known crystals of marcasite from the sedimentary strata of this country are the beautiful specimens from the Chalk Marl, between Dover and Folkestone.f They are usually groups of twin crystals of the spear-head type, supposed locally to be heads of Roman weapons. J Some excellent examples, attached to the matrix, are here exhibited (No. 1425). According to Prof. Hartley's spectroscopic studies, the marcasite of Dover contains thallium and nickel. The Chalk of the south-east of England likewise contains, especi- ally in its lower zones, much marcasite in the form of nodules, some- times spherical but often most capricious in shape, and displaying when broken a fibro-radiate structure (No. 1426). The exterior is often rusty, by limonitisation, but the freshly fractured surface is brilliantly metallic and of pale yellow colour. According to Mr. H. N. Stokes|| the colour of pure marcasite is tin white, and Prof. Julien makes the same remark, but tarnish or admixture with pyrite renders it brass-like. Exposure rapidly induces a yellow tarnish, which may pass into a brown colour. The nodules, often known locally as ' thunderbolts ' and ' fairy-balls,' may enclose an organic nucleus ; or a hollow may be left by disappearance of a fossil, and in this cavity pulverulent sulphur sometimes occurs a substance set free by the disintegration of the molecule of iron disulphide. Some observers have recorded microscopic organic structure in the substance of the nodules. It has been pointed out by Mr. Stokes that a fibrous structure affords no clue to the species. " Fibrous pyrite appears to be much more common than fibrous marcasite." Of all metallic sulphides, marcasite seems the most unstable, and its instability is generally responsible for the decomposition which * See, for example, Dr. Sadebeck's communication to the Neues Jahrb. Min. (1878), p. 289. " Ueber den Namen ' Markasit '." j- " Remarks on the Chalk Cliffs in the neighbourhood of Dover." By William Phillips. Trans. GeoL Soc., vol. v. (1821), p. 36. J Prof. Miers's " Mineralogy," p. 330. " The wide Dissemination of some of the Rarer Elements, etc." Jatim. Chem. /Soc., vol. Ixxi., part i. (1897), p. 533. II Bull. U.S. GeoL Surv., No. 186, 1901. QUARTS. 199 pyritised structures frequently suffer. Several examples of fossils mineralised with iron disulphide will be found in the Case illustrating Fossilisation. The pyritic nodules, more or less altered, occurring in the Gault of Cambridgeshire are known locally as " rugg-s tones."* Iron-pyrites, generally marcasite, was formerly used, like flint, for eliciting sparks by impact with steel ; hence in old works there is sometimes confusion between pyrites and flint, both substances being called " fire stone " (Feuer stein).] The original word pyrites has similar reference to the use of the mineral in striking fire. Quartz (Nos. 1427 to 1433). Crystals of quartz occur under various conditions in many of the Neozoic rocks. Some of the finest examples are found in the Dolomitic Conglomerate, especially in the interior of the potato- stones of Bristol and the Mendip area. These have already been noticed (p. 113), but in addition to the specimens exhibited in Case VII. another is placed here in order to illustrate the minerals yielded by the Trias (No. 1427). The agates of the Dolomitic Conglomerate on disintegration of the rock, may be preserved in the resulting detritus, and probably in this way the agates of the Litchfield drift have been derived. These agates are curiously altered, as seen in No. 1428, or still better in the large series, presented by Spencer G. Perceval, Esq., and exhibited in the Table-case of agates on the opposite side of the museum. In the Litchfield agates there are certain zones which have become dull and soft so that they adhere to the tongue, whilst some are reduced to a white opaque substance so soft as to yield to the finger nail.J Probably some of the layers contain both crystalline and colloidal silica, and the latter may be dissolved out by waters containing alkaline carbonates, or organic acids, leaving a residue which will be porous in consequence of the removal of the soluble part, and dead white by reflection of light, from the walls of the solution pores. The effect will be similar to that presented' by the surface of certain weathered flints. Such de-opalised .flint is sometimes known as Passyite. J O Quartz occurs in fairly large crystals under circumstances of rather exceptional character in the fuller's earth beds worked in the Lower Greensand at Nutfield in Surrey. The specimen No. 1429 shows the association of the colourless crystallised quartz with honey- yellow barytes. In some cases the Nutfield quartz presents a tint distinctly amethystine. It may be noted that the quartz is of subsequent formation to the barytes and occupies the space between the barytes-crystals. *Mem. Geol. Surv. " Geology of Cambridgeshire." By A. J. Jukes-Browne, t See, for example, Sir John Pettus's Fleta Minor, 1683. j " Notice of some Peculiarities observed in the Gravel of Litchfield." By A. Aikin, Esq. Trans. Geol. Soc., vol. iv. (182 ), p. 426. Lacroix's " Mineralogie de la France," t. iii. (1901), p. 132. MINERALS OF THE NEOZOIC STRATA* Some of the best examples of quartz from the Cretaceous beds are the crystals often found lining the interior of hollow flints from the Chalk, of which No. 1430 is a specimen. No. 1431 is an example of chalcedony, or microcrystalline silica, forming a mammillary coating on the walls of a cavity in a flint, whilst in No. 1432 the chalcedony hangs from the upper part of the hollow in small pendant stalactites. The specimen No. 1433 illustrates the curious conoidal fracture of flint a character apparently connected with the uniformity of grain and mechanical isotropism of the flint. No attempt is here made to represent the varied forms and characteristics of Flint, as a large series of specimens will be found in the Petrographical collec- tion, whilst others are seen in Section P of the Horse-shoe Case. Allophane (Nos. 1434 to 1436). In 1856 the occurrence of Allophane was noticed at the chalk pits at Charlton, in Kent, by some of the students of the Royal School of Mines. Its mode of occurrence was described by Prof. Morris,* and the mineral was analysed by Mr. A. Dick and by Mr. Northcote, who was attached at that time to the Royal College of Chemistry. The allophane, known to the quarrymen as " petrified water," occurred as a white, yellow or brown amorphous substance, in nodules or irregular layers, often lining fissures and funnel-shaped cavities in the chalk, just at the junction of the Thanet sands (Nos. 1434, 1435). Mr. Northcote regarded it as a silicate of alumina with a variable amount of neutral hydrate.f It seems to be a product of the decomposition of certain aluminous silicates. Allophane was discovered by the late Dr. Charles Berrill in the Northampton sand worked for ironstone, and the substance was analysed by Mr. Douglas Herman. J A specimen is shown in the Horse-shoe Case. Related more or less nearly to allophane is the mineral substance known as Scarbroite a hydrated silicate of aluminium, with a small proportion of silica, falling in some cases below 8 per cent. The mineral was discovered near Scarborough, by the Rev. W. Vernon Harcourt, and has been described by Mr. Fox Strangways as occurring in small veins in the Grey Limestone and in the Estuarine series above. A specimen of scarbroite is exhibited as No. 1436. * " On the Occurrence of Allophane at Charlton, Kent." Quart. Journ. Geol. Soc., vol. xiii. (1856), p. 13. See also Mem. Geol. Surv. " The Geology of London." By W. Whitaker, B.A., F.R.S., vol. i. (1889), p. 527. Mr. Whitaker gives a list of the few minerals which occur in the London district. f " On the Constitution of Allophane." Phil. Mag. (4), vol. xiii. (1857), p. 338. % Quart. Journ. Geol. Soc., vol. xxvii. (1871), p. 234. See also Mr. Sharp's paper : " The Oolites of Northamptonshire." Ibid., vol. xxvi. (1870), p. 367. Mem. Geol. Surv. " The Jurassic Rocks of Britain," vol. i., Yorkshire, 1892, p. 475. ALUMINITE, ETC. 201 Aluminite or Websterite (Nos. 1437 to 1439). In the early years of the last century pieces of this substance were picked up by Mr. Thomas Webster, on the beach between Brighton and Beachy Head.* It was described as a white substance resem- bling tobacco-pipe clay, and was at first regarded as pure alumina, but was shown by Wollaston and Smithson to be a hydrous sub- sulphate of alumina.f This mineral, called Websterite by most geologists, but known also as Aluminite a name which, according to the law of priority, it ought to enjoy occurs typically in the form of reniform masses, with a micro-crystalline structure, found at the junction of the Tertiary beds with the Chalk, especially at Newhaven (Nos. 1437, 1438). Its origin is not difficult to understand. Free sulphuric acid is readily formed by the oxidation of pyritic minerals, and this acid might decompose the silicate of alumina in the clays of the Lower London Tertiary series, or in other clays upon the chalk, with production of an aluminium sulphate. Many years ago Mr. Spencer G. Perceval called attention to some deposits of websterite exposed in excavations at several localities in Brighton, where they occurred a few feet below the surface, in association with limonite and selenite, as seen in some of these specimens. J A very large mass of this Brighton websterite will be found in the Hall of the Museum, under a Table-case on the eastern side, near the window, and a small specimen is placed in this Case (No. 1439.) The brown ochreous material represents the iron of the pyrites, whilst the selenite has been formed from the chalk, or from shells, by the action of sulphuric acid, set free on decomposition of the pyrites. Some of this websterite is coated with a black deposit, in which the )ate Dr. Flight found manganese and cobalt. In describing the websterite discovered during the drainage works in the Montpelier district in the N.W. of Brighton, the late Mr. James Howell remarked that the mineral was found rather plenti- fully in chalk districts wherever pyrites was associated with clay. Some confusion has been introduced into nomenclature by the fact that the name websterite has also been given to a certain pyroxenitic rock. There is consequently the more reason why the name should be detached from the mineral, and the mineral distinguished as aluminite. Calcite (Nos. 1440 to 1444). Crystals of calcite may occur in the fissures of any calcareous rock, and are common in many Neozoic limestones. Such crystals, how- ever, are generally not equal in size or in beauty of form to those from the older rocks or from mineral veins. A few examples of calcite from limestones and other deposits of Secondary age are here exhibited. In the Triassic beds, calcareous * Ann. Phil. vol. i. (1813), p. 467. t Ibid., vol. ii, (1813), p. 238. + G&ol Mag., Vol. viii. (1S71), p. 121. V Rep. Brit. Assoc., Brighton, 1872, pp. 108, 109. 7882. P 202 MINERALS OF THE NEOZOIC STRATA. spar occasionally occurs, and is usually coloured red with oxide of iron, as in No. 1440. Crystals lining the potato stones from the Dolomitic Conglomerate are similarly tinted, as shown in Case vn. The rock from near Wells, described by Buckland and Conybeare under the name of "wonder stone," was a breccia containing yellow transparent crystals of calcite in a dark red dolomitic matrix.* In the interior of fossil shells calcite is not infrequent. No. 1443 shows the mineral crystallised in the cavity of a Terebratula from the Great Oolite. No. 1441 represents the columnar calcite, known from its colour and structure as " sugar candy," occurring in fissures in the Portland quarries. Fibrous calcite from the Purbeck beds is often termed by quarrymen *' beef " a name suggestive of its resemblance to the fibres of muscular tissue. The specimen No. 1442, presented by Clement Reid, Esq., F.R.S., is a good example of crystallised calcite from the Upper Chalk of Corfe Casth. Calcareous deposits, of stalagmitic and stalactitic character, are common in the cavities in calcareous rocks of all ages, and are in course of formation at the present time whenever waters containing carbonate of calcium percolate through the rocks under conditions which favour precipitation. Stalactites of recent formation may often be seen hanging from the soffits of railway arches, for even when the arch is built of brick the mortar furnishes a supply of lime. A series of stalactites and stalagmites will be found in the Collection of rock specimens at the southern end of the Museum. Jet and Amber (Nos. 1445 and 1446). A few substances generally regarded as minerals but evidently formed, directly or indirectly, from organic sources, are here grouped together, at the end of the series of specimens representing the mineral resources of Southern Britain. Among these so-called " organic minerals " Jet occupies a conspicuous place. It appears, however, from the official statistics that no jet has been obtained in this country since 1897. The jet, formerly worked rather extensively at Whitby in York- shire, occurs there in the Upper Lias stales. It is usually regarded as a compact variety of lignite, and, indeed, some varieties show ihv microscopic structure of coniferous wood, but the tissues seem to be impregnated with bituminous matter, and in many cases the vegetable structure is completely obliterated. A jet-like substance occasion- ally forms the mineralising material of certain fossils, especially the scales of fishes ; drops of liquid bitumen occur in the chambers of ammonites and in the interior of nodules in the jet rock ; and in- flammable gases sometimes accumulate in the old workings. It seems not unlikely that masses of vegetable matter like tree trunks may have sunk, water-logged, in the black mud of the Liassic sea the mud itself partly derived, perhaps, from the disintegration of the *Mem. Geol. Surv. " Geology of East Somerset." By H. B. Woodward, F.R.S., 1876, p. 63. - JUT, AMBER, ETC. 203 Coal Measure shales, and the material thus buried, without access of air, would undergo conversion into a lignitic substance, whilst a kind of natural destructive distillation yielded bituminous matter which saturated the product.* Mr. A. C. Seward finds that much of the Whitby jet was formed from drifted wood of Araucarian type, f Jet was formerly obtained from nodules picked up on the beach, but when this supply became exhausted the cliffs were attacked, and the jet-rock ultimately worked by simple burrowing. On the Norfolk coast, in the neighbourhood of Cromer, jet is occa- sionally thrown up on the beach, especially after east winds. This appears to be different from Yorkshire jet, and is regarded by Mr. Clement Reid as probably derived from Lower Tertiary beds, buried under the North Sea. To a similar source must probably be referred the Amber which is sometimes found on the coast of East Anglia. A few pieces of such amber are here shown (No. 1446), and some finer specimens will be found in Section C of the Horse-shoe Case, including a piece of pale clouded amber, dredged off Yarmouth, weighing as much as 37 ozs., and another piece, differing markedly from the former by its deep orange colour, found on the coast of Cromer, and weighing 28J ozs.J The specimens in the tray No. 1446 were presented by C. Reid, Esq. Copaline, etc. (Nos. 1447, 1448). Various mineral resins, more or less allied to amber, yet rarely if ever suitable for ornamental purposes, occur occasionally in the stratified rocks of Britain. No. 1447 is an example of such a sub- stance from the Upper Greensand of Black Gang Chine, in the Isle of Wight ; whilst No. 1448 is a specimen of the well known fossil resin from the London Clay of Highgate, often called Copaline, or High- gate Resin. This was first detected nearly a century ago by Mr. B. G. Snow, a local surgeon, whilst the tunnel was being driven through HighgateHiH. Sowerby, writing in 1817, speaks of a great quantity having been found, " perhaps a peck or two," but most of it dis- appeared by disintegration. Samples were sent by Sowerby to Dr, Thomas Thomson, who was led from his analysis to regard it as approaching nearest in character to copal and amber.|| Its chemical properties, however, according to the doctor, threw no light on its *0n the occurrence of jet at Whitby see Mem. Geol. Surv. " The Geology of the Country between Whitby and Scarborough." By C. Fox-Strangways and G. Barrow, 1882. " The Geology of North Cleveland." By G. Barrow, 1888 ; and " The Jurassic Rocks," vol. i., Yorkshire. By C. Fox-Strangways, p. 455. Also, " The Geology of Yorkshire." By R. Tate and J. F. Blake. t Pep. Brit. Assoc. for 1903, p. 841. % On East Anglian amber and jet, see Mem. Oeot. Surv. " The Geology of the Country around Cromer." By Clement Reid, F.R.S., 1882, p. 133. Also, 4 On Norfolk Amber," by same author, Trans. Norfolk Nat. Soc., vol. iii. (1884), p. 601. Ibid. vol. iv. (1886), p. 247. " British Mineralogy," vol. v., p. 230. |j " Description of a Resinous Substance Lately Dug Out of the Earth at Highgate." Ann. Phil., vol. ii. (1S13), p. 9. 7882, P 2 201 MINERALS OF THE NEOZOIC STRATA. origin, and could not, to use his words, " facilitate our enquiries into the revolutions which the southern part of this kingdom has under- gone, and the various animal and vegetable remains so thickly scattered in its bowels." As a matter of fact, the substance seems to be merely a resinous exudation from certain coniferous trees which flourished on the land drained by the great London Clay River. It was found not only in small lumps in the clay, but attached to fossil wood, bored by teredo, and in some cases on septaria, whilst it was frequently associated with pyrites. According to Prof. F. W. Johnston, who analysed a large series of carbonaceous minerals, the Highgate substance is nearly, if not absolutely, identical in constitution with the gum anime of Cayenne.* It was this, or a similar body, that was described by Dr. Wetherell, in 1838, as having been found in the railway cutting at Chalk Farm, where it was associated with much pyrites, and also in a septarium at Highgate Archway, close to certain vegetable remains. The relation of the pyrites to the resin may be sufficiently explained by the reducing action of the carbonaceous matter. It seems likely that it was a resin of like character that is referred to by Dr. John Woodward, when he speaks of " amber, brown and fossil, found at least thirty feet deep in the pit where they dig clay to make tiles at Richmond, Surrey " ; and he adds : " The workmen call it rosin." True amber is said to have been found in the gravel pits at Kensington. Certain mineral hydrocarbons have already been referred to as occurring among the older rocks (p. 178), and other bituminous sub- stances are occasionally found among the Neozoic strata. These may assume the solid form of asphalt, or the liquid state of petroleum, or even the gaseous condition. Natural gas is now obtained indus- trially at Heathfield, in Sussex, where it appears to rise from sands and sandstones of the Lower Wealden beds and from certain Purbeck^ strata. The occurrence of the gas at Heathfield was described by Mr. Charles Dawson.f soon after its discovery, and has recently been the subject of some geological observations by Mr. H. B. Woodward. J * " On the Composition of Certain Mineral Substances of Organic Origin : vi. Highgate Resin, or Fossil Copal." Phil. Mag., vol. xiv. (1839), p. 87. f " On the Discovery of Natural Gas in East Sussex." Quart. Jonrn. Geol. Soc., vol. liv. (1898), p. 564. :j: " Notes on the Occurrence of Natural das at Hoathficld, Sussex." Mem. Ccd. Surv. Summary of Progress for 1902, p. 105. MINERALS OF SCOTLAND. 205 DIVISION 2 MINERALS OF SCOTLAND. MINERALS OF THE LEADHILLS DISTRICT. (Nos. 1449 to 1504.) A collection fairly representative of the minerals of Scotland is exhibited, partly in Case XI and partly in Case XII. According to a List communicated to the British Association in 1901, by Mr. J. G. Goodchild, there are about 180 species of mineral known to occur in Scotland.* The collection here exhibited, though containing some very fine specimens, cannot be regarded as large when compared with the extensive display of local minerals in the Royal Scottish Museum in Edinburgh, which includes the famous collection made by the late Dr. Heddle. For further information respecting the minerals of Northern Britain the visitor may be referred to the comprehensive work on " The Mineralogy of Scotland," by this authority, published posthumously, under the editorship of Mr. Goodchild. | The first group of Scottish minerals exhibited in the Case now under notice illustrates the well-known ore-deposits of the mining country around Leadhills, in the south of Lanarkshire, and the neigh- bouring district of Wanlockhead, on the borders of Dumfriesshire. Here, in a wild and elevated tract of the Southern Uplands, veins of lead ore, coursing through rocks of Lower Silurian (Caradoc) age, have been worked from a very early period. J Documentary evidence traces the history back to the thirteenth century, but according to some authorities mining was probably carried on here during the period of the Roman occupation, or even in prehistoric It is not, however, simply the lead-ore which has rendered this district famous in the annals of British mining. Gold was formerly found in considerable quantity, and even now grains of the precious metal may occasionally be obtained by washing the alluvium of the burns. The gold of Crawford Moor is said to have been discovered in the reign of James IV., and the celebrated " bonnet pieces " were minted of this metal. At various periods in the course of the sixteenth century, considerable activity prevailed, and at one time * " A List of the Minerals known to occur in Scotland."- Rep, Brit. Ass., Glasgow, 1901, p. 649. | " The Mineralogy of Scotland." By the late M. Forster Heddle, M.D. Edited by J. G. Goodchild. 2 vols. Edinburgh, 1901. % The geological structure of the district is described in Mem. Geol. Surv. " The Silurian Rocks of Britain, vol. h, Scotland."- By B. N. Peach, F.R.S., and John Home, F.R.S.E. With Petrological Chapters and notes by J. J. H. Teall, M.A., F.R.S., 1899. " The Silurian Districts of Leadhills and Wanlockhead, and their Early and Recent Mining History." By John R. S. Hunter, D.Sc., LL.D. Trans. Geol. Soc. Glasgow, vol. vii. (1885), p. 373. 206 MINERALS OF SCOTLAND. Sir Bevis Bulmer worked to such good purpose that he was able to present to Queen Elizabeth a porringer made of gold from this locality. Nuggets weighing several ounces each, in one case reaching as much as 30 ozs., have been recorded.* It is probable that the gold of this district has been derived from the disintegration of pyritic quartz -veins. Heddle refers to a brown iron-ochre from the Scar Burn, on the upper waters of Wanlock, which yielded more than five dwts. of gold to the ton.f This may well have been a gozzany ore, resulting from the alteration of auriferous pyrites. At the present time, the Museum is not in possession of any examples of the gold of Crawford Moor. The few specimens of Scottish gold exhibited in Wall-case 14 were obtained, in 1860, from Kildonan Burn, in Sutherlandshire.J Silver is yielded to a moderate extent by the lead- ore of the Southern Uplands. In 1902 the mines of Wanlockhead produced 899 tons of lead-ore yielding 4,944 ounces of silver ; whilst those of Leadhills turned out 730 tons of ore, with 2,555 ozs. of silver. Two excellent examples of crystallised galena are here exhibited as No. 1449. In the shallow workings of the lodes in the Leadhills district, a great variety of oxidised products was formerly obtained, including several species not found elsewhere in Britain, or found only in the lead- veins of Caldbeck Fells in Cumberland (p. 152). The rarer minerals were obtained almost exclusively from the Susanna Mine at Leadhills. Excellent representatives of all these species, such as are to be found only in collections made many years ago, are ex- hibited in the Case now under review. No. 1450, according to an old label, is a specimen of Minium, or native red lead, from Leadhills. This rare mineral, appearing here as a pulverulent incrustation, of brilliant scarlet colour, is evidently an alteration-product of other plumbiferous species. The authenti- city of specimens of minium in old collections is not always free from doubt, but there seems no reason to regard this specimen as other than genuine. * See " The Disco verie aid Historie of the Gold Mynes in Scotland." By Stephen Atkinson. Printed by the Banantyne Club, Edinburgh, 1825. Also, " Early Records relating to mining in Scotland. Collected by R. W. Cochrane-Patrick of Woodside." Edinburgh, 1878. Reference may be made to several papers on Scottish gold by Dr. Lauder Lindsay, such as " The Gold and Gold-Fields of Scotland." Trans. Edin. Geol. Soc., vol. i. (1870). p. 105. See too " Historical Notes on the Occurrence of Gold in the South of Scotland." By Patrick Dudgeon, Min. Mag., vol. i. (1877). p. 21. Also: "The Occurrence of Gold in Great Britain an I Ireland. " By J. Malcolm Maclaren. Trans. Inst. Min. Eng., vol. xxv. (1904). p. 435. t " The Mineralogy of Scotland," vol. i., p. 7. { On the occurrence and probable source of the Sutherlandshire gold, s?e Mr. E Greenly's "Notes on the Sutherland Gold-Field." Trans. Edin. Oeol. Soc., vol. vii. (1899), p. 100. This paper contains a bibliography of the subject. Home Office Report for 1902, p. 244. LEAD-ORES O LEADHILLS. 207 A good suite of specimens, numbered 1451 to 1456, serves to illustrate the occurrence of Cerussite, or lead carbonate, in the veinstones of Leadhills. Cavities within the zone of oxidation not infrequently contained this mineral, crystallised in well-defined forms, and associated with other oxidised lead- ores in such relation- ship as to suggest a rather late origin for the cerussite. The crystals in No. 1455 present a blackened appearance, due perhaps to the action of sulphuretted hydrogen. Mr. Goodchild has suggested that the lead-grey colour of some of the cerussite may be due to the presence of lead dioxide. The Leadhills district was at one time rather remarkable for the beauty and variety of its crystallised cerussites.* Pyromorpkite, or chloro-phosphate of lead, finds illustration in the specimens Nos. 1457 to 1460. Whilst some of these examples of the mineral are of green colour, others are yellow, orange, and even red. The bright orange-coloured variety, which was raised in the Susanna Mine, has been sometimes regarded as a chromo-phosphate ; but Dr. Norman Collie remarks that no chromium is revealed by the analyses. t Probably certain compounds of vanadium may be responsible for the tints in some of the coloured phosphates. Isomorphous with pyromorphite, is the mineral called Vanadinite, a vanadate of lead, for which the mines of Wanlockhead have been in their day rather famous. This rare mineral, as seen in Nos. 1461 to 1464, crystallises in small hexagonal prisms, but is usually found in globular aggre- gates, of pale brown colour. Dr. Heddle records a crystal formed partly of vanadinite and partly-of pyromorphite a striking proof of the isomorphism of the two species. According to Mr. Goodchild " the vanadium in the Leadhills Mines may possibly have originated through the decomposition of the ferro-magnesian silicates present in the Arenig lavas there, as small traces of vanadium can usually be detected in the fresh minerals in question. "{ The wide distribu- tion of vanadium is attested by the spectroscope. Some excellent examples of Anglesite, or lead sulphate, are exhibited here as Nos. 1465 to 1472. These show the characteristic dagger-shaped crystals, of exceptional size and perfection. The association of the mineral with decomposed galena in No. 1470, at once betrays its origin. Far more interesting, however, than the simple sulphate of lead are the crystallised basic sulphates and sulphato-carbonates, for which the Leadhills district is renowned. Lanarkite, considered to be the rarest of all the minerals of Lead- hills, is a basic sulphate of lead, which was originally described as a sulphato-carbonate. It occurs in small monoclinic prisms, and in diverging aggregates of long slender crystals ; some of the crystals * See Mr. J. G. Goodchild' s " Contributions to Scottish Mineralogy.'! Proc. Roy. Soc. Edin., vol. xxiv., part iii. (1902), p. 321. f " On some Leadhills Minerals.'- Journ. Chem. Soc., vol. Iv. (1889), p. 91. ' Contributions to Scottish Mineralogy." Op. cit., p. 338. 1508 MINERALS OF SCOTLAND. presenting a pale greenish tint. The characters of the mineral and the nature of its associates are well seen in the specimens, Nos. 1473 to 1478. According to Heddle this species was found only at the Susanna Mine. Among the accompanying minerals will be noted a group of other secondary species, such as caledonite, leadhillite, linarite and cerussite, with galena, the parent- mineral of the whole family. The beautiful crystals of Linarite will arrest the attention of the visitor by their fine azure-blue colour a colour which has occasion- ally led to the mineral being mistaken for chessylite, or. blue carbonate of copper. Whilst lanarkite is a basic sulphate of lead linarite is a basic sulphate of lead and copper. It has already been referred to in connection with its occurrence at Rough ten Gill (p. 157), but the Leadhills specimens here exhibited (as Nos. 1479 and 1480) are even finer than those in Case IX. from the Cumber- land locality. Caledonite, one of the rarest minerals of Leadhills, is another basic sulphate of lead and copper, though originally described as a cupreous sulpha to -carbonate of lead. It occurs in small greenish-blue crystals of prismatic habit, as shown in the specimens Nos. 1481 and 1482, where it occurs in association with leadhillite and lanarkite. Dr. Collie suggested that caledonite might be regarded as a hydrated form of lanarkite, in which lead was partly replaced by copper. A fine series of specimens, comprised under Nos. 1483 to 1492, represents the characteristic species named Leadhillite. This is a basic sulphate-carbonate of lead, occurring in crystals of tabular habit, belonging to the monoclinic system, and presenting a marked pearly lustre on the cleavage-planes. According to Dr. Heddle, it occurred in all the mineral veins of the Leadhills and Wanlockhead Mines. Closely related to the true Leadhillite, of which it is probably but a variety, is the mineral named Susannite, after its occurrence in the Susanna Mine at Leadhills. Optically it presents uniaxial char- acters ; but Prof. Groth suggests that this may be due to repeated lamellar growth.* It has been pointed out by Mr. L. J. Spencer that three distinct kinds of leadhillite may be recognised : first, the ordinary monosymmetric leadhillite ; secondly, the susannite which has been described as rhombohedral ; and thirdly, an ortho- rhombic type, which he has found in the old lead slags of the Mendip Hills (p. 108).f Although similar to each other in general external characters, each kind has probably a definite chemical composition, and discrepancies in the analyses may be due to intimate admixture of these varieties. Dr. Collie has called atten- tion to the apparent inconstancy in the ratio of the sulphate and carbonate in this species. Nos. 1489 to 1492 are specimens of susannite, exhibiting its^typical characteristics. * " Tabellarische Uebersicht der Mineralien." 4 ed. 1898., p. 71. f " Leadhillite in ancient lead-slags of the Mendip Hills." Hep. Brit. Ass., Bristol, 1898, p. 875 ; Geol. Mag., new ser., Dec. 4, vol. vi. (1899), p. 71. JttfcEfcALS OF LtiADJULLS* 209 Ores of zinc occur, to a limited extent, with those of lead in the veins of the Leadhills district. Blende, as usual, is associated with the galena ; but though fine crystals are occasionally found they are not common, and there are at present no examples in the collection. The silicate of zinc, previously noticed under the name of Hemimorphite, occurs at Wanlockhead ,sometimes in acicular crystals, but more often in massive or botryoidal forms, not in- frequently invested with variously coloured pyromorphite. As an example of its comparatively recent formation, Dr. Heddle records its occurrence as a chalky deposit on some old timber at the Bay Mine, Wanlockhead.* Calamine, or carbonate of zinc, is not included as a Scottish mineral in Mr. Goodchild's List. In the year 1902 there were raised at Wanlockhead 110 tons of zinc-ore. Associated with the lead and zinc ores of the Leadhills tract, copper -pyrites and its various alteration products occur in sub- ordinate quantity. No. 1493 is a specimen of Malachite, showing by its association with galena and with cerussite that both the lead and the copper ore have suffered conversion into carbonates. In the rare species Aurichalcite, represented by Nos. 1494 and 1495, copper and zinc occur together as a basic carbonate, though free carbonate of zinc, as previously noted, is not recorded from these deposits. The aurichalcite occurs in delicate acicular crystals, forming divergent groups, of a pale green or sky-blue colour, associated with the rare species, lanarkite. With these Scottish specimens of aurichalcite may be compared the examples of the same mineral from Cumberland in Case IX. (p. 158). Several specimens are exhibited in illustration of the various sparry minerals which occur in the veinstones of the Leadhills Mines. No. 1496 is a geode of barytes, and No. 1497 a specimen of caldte in opaque white scalenohedra, on which are seated small saddle-shaped crystals of pale brown dolomite. Most of the Lead- hills calcite contains, according to Dr. Collie, more or less carbonate of lead, and when the proportion becomes notable the mineral is usually called Plumbocalcite a name given to it in 1829 by Prcf. J. W. Johnston. This plumbiferous calcite occurs in dull white rhombohedra, rather denser than pure calcite. It is regarded as an isomorphous mixture of the carbonates of lead and calcium in variable proportion, and is theoretically interesting since it suggests the existence of a rhombohedral carbonate of lead. This compound is therefore probably dimorphous, forming an ortho- rhombic species the ordinary cerussite, which corresponds to aragonite, and a rhombohedral species not yet known in a free state. Just as the two rhombohedral species occur together in plumbocalcite, so the two orthorhombic species are associated in the mineral called Tarnoivitzite.-f Dr.Norman Collie has published analyses of Plnmbo-aragonite from Leadhills, proving that the *"The Mineralogy of Scotland, vol. ii., p. 73. | See Prof. Miers' " Mineralogy," p. 227, 210 MINERALS OF SCOTLAND. aragonite of this locality may contain a small proportion of lead carbonate, though his specimen was not so highly plumbiferous as the typical tarnowitzite of Silesia.* Some excellent examples of Aragonite from Leadhills are exhibited here as Nos. 1501 to 1503. In one specimen (1501) the mineral occurs in white slender crystals on calcite, whilst in the other specimens the crystals are of a delicate sea-green tint, acicular in habit and disposed in divergent groups. Dr. Heddle examined some green crystals from Leadhills, which had been regarded as strontianite, but found that they contained only 1-7 per cent, of carbonate of strontia, and were practically aragonite. f With regard to the origin of the minerals at Leadhills, it is probable, as Mr. Goodchild suggests, that although the metalliferous veins may have had a very complicated history, the introduction of much of the mineral matter may have been due to the uprise of thermal solutions in fault-fissures during the later phases of volcanic activity in Tertiary times. MINERALS FROM STRONTIAN. (Nos. 1505 to 1516.) Although the minerals of Strontian ought strictly to be placed with those of the Highlands in Case XII., it has been deemed de- sirable to sacrifice the topographical arrangement in order to utilise the space left in Case XI. at the end of the Leadhills series. Hence the minerals of Strontian are here placed in immediate sequence to those of Leadhills. Deposits of lead-ore near the little village of Strontian, in Argyll- shire, were opened up at the beginning of the eighteenth century, and continued to be worked for rather more than 150 years. The ore occurred in veins, coursing through gneissose rocks, near their junction with the granite. Nos. 1505 and 1506 are samples of the galena, and many other specimens will be found in Wall-case 45. The museum is fortunate in possessing a rather large series of the Strontian minerals, principally from Bellsgrove and Fee Donald Mines, presented by the late Sir James Miles Riddell, Bart., at the close of the Great Exhibition of 1851, where they had been exhibited. In Section I. of the Horse-shoe Case are several examples of the Calcite from the Strontian lead-lodes, whilst in the case now under notice the species is represented by Nos. 1507 and 1508. One of these specimens shows the calcite in the form of " Slate spar," or Schieferspath the tabular habit being determined by development of the basal pinacoid. The opaque white plates of this spar are seated on brown calcite, which is crystallized in obtuse rhombohedra, deeply striated and marked by dark radiating lines running along the short diagonals of the rhombs. Barytes also occurs in the vein-stone of the Strontian lead-lodes. * Journ. Cliem. Soc., vol. Iv. (1889), p. 95. f ' Minerals New to Britain.'' Min. Mag., vol. v. (1884), p. 22. MINERALS OF STRONTIAN. 211 The \riViage of Strontian is famous for having given its name to the element strontium. This metal occurs here in the form of the carbonate, known as Strontianite. It appears that the mineral was found as far back as 1764, and was at first regarded as carbonate of baryta. But in consequence of its property of imparting a reddish colour to flame it was suspected by Crawford, in 1790, to contain a new earth a suspicion independently expressed by Cruikshank, and soon afterwards confirmed by Dr. Hope, of Edinburgh, who in 1792 determined the existence of a peculiar substance which he named after the Strontian spar in which it was discovered. The metal strontium was isolated by Dav> in 1808. Strontianite is here represented by Nos. 1509 and 1510, whilst the visitor is referred for other and larger specimens to Section G of the Horse-shoe Case. Distinct crystals are rare, but the mineral usually occurs in fibrous masses, the colour of which is sometimes pale green as in No. 1509, sometimes dark brown as in No. 1510. Strontianite is an orthorhombic species, isomorphous with witherite and aragon- ite. The mineral frequently contains barium, partially replacing the allied strontium.* Just as witherite may be converted into barytes by the action of certain sulphates, such as those resulting from de- composing pyrites, so Strontianite may be altered to celestite ; and it is not surprising, therefore, to find that this species occasionally, though rarely, occurred at Strontian. The remaining specimens in this Case represent two rather rare and interesting species, known as brewsterite and harmotome minerals belonging to the group of hydrous silicates termed zeolites, to which attention will be specially directed in the description of Case XII. (p. 215). Nos. 1511 and 1512 show the Brewsterite in small brilliant crystals of prismatic habit, belonging apparently to the monoclinic system. The crystals are striated longitudinally, by repeated twinning, and present a pale yellowish brown colour. In No. 1512 the crystals are seated on Strontianite. The mineral is a hydrous silicate of aluminium, strontium, barium and calcium, and may be regarded as a kind of heulandite (p. 217) in which calcium is partly replaced by strontium and barium. It was found chiefly in the Bellsgrove lead-mine, and was described by Mr. Brooke, who named it after Sir David Brewster (b. 1781, d. 1868). Although the zeolites are characteristic minerals in the cavities of eruptive rocks, they also occur to a limited extent in certain mineral veins. This is notably the case with Harmotome, which occurs typically in the silver-lead veins of Andreasberg, in the Hartz, as also in the lead-lodes of Strontian, especially in the old Bellsgrove Pit. It is a zeolite which, like brewsterite, contains barium, but, unlike brewsterite, no strontium. The mineral crystallizes, it is generally believed, in the monoclinic system, but always in twins ; and a characteristic habit is that of two complex sub-individuals interpenetrating, so as to produce a cruciform * " Analysis of a sample of Strontianite, from Strontian, Argyllshire." By W. Ivison Macadam. Min. Mag., vol. vi. (1886), p. 173. 212 MINERALS OF SCOTLAND. group, whence the name "cross stone," which is sometimes applied to this species. The crystals from Strontian are bold and sharply denned, often of opaque white colour. The small colour- less crystals of harmotome are sometimes distinguished as a variety under the name of Morvenite, a name derived from a locality in Argyllshire. The characters of the species are well represented by the specimens Nos. 1513 to 151G. Some of these show the harmo- tome associated with calcite, and it occurs also in companionship, as might perhaps be expected, with the other barium-bearing minerals, barytes and brewsterite. The zeolites in the veins at Strontian may have been derived from the alteration of the felspars in the neighbouring granitic rocks ; but although certain felspars contain barium the source of this element is more likely to be explained by reference to the barytes which occurs in the lodes. As Mr. Goodchild remarks, harmotome is one of the latest formed minerals in the veins at Strontian. It is suggested by this authority that the rocks of Strontian may have been covered by Tertiary basalts, and that the metalliferous mine- rals may have been introduced into fissures by the uprise of thermal waters towards the close of the volcanic period. The zeolites are probably of subsequent formation.* * " The Natural History of Scottish Zeolites and their Allies." Trans. Geol. Soc. Glasgow. Supplement, ^ol. xii., 1903. MINERALS OF THE MIDLAND VALLEY. 213 CASE XII. DIVISION 1. MINERALS OF SCOTLAND. MINERALS OF THE MIDLAND VALLEY. (Nos. 1517 to 1560.) Many of the eruptive rocks which are so extensively developed in the great Midland Valley of Scotland yield various minerals of secondary origin, especially zeolites, of which a representative collection is here exhibited. Such minerals occur usually in the vapour cavities of the vesicular lavas, chiefly of andesitic type, which are referable to the early part of the Carboniferous period. Most of the specimens are from the volcanic rocks of the Clyde plateau some from the south side of the estuary, notably from Boylestone Quarry in Renfrewshire, and others from the Campsie and Kilpatrick Hills, on the north.* In addition to the zeolites, a 'few other minerals occur in these ancient lavas. No. 1517 is a specimen of the Native Copper occasion- ally found in Boylestone Quarry, near Barrhead. This example, presented by Mr. Graham of Craigallian, shows the metal as a brilliant film on a joint-plane of the rock, as though electro-deposited on the wall of a fissure. Mr. Goodchild has suggested that in such cases the metal may have been dissolved out of the eruptive rock through which it was disseminated, and reduced perhaps from the state of carbonate by decomposing organic matter.} He also points out that in this quarry the native copper occurs occasionally as enclosures in calcite, and that the crystals of calcite are then more than usually complex in form. The metal is likewise found here in association with prehnite, to which it sometimes imparts a brown colour. The association with prehnite and calcite rather recalls the con- ditions under which native copper occurs in the amygdaloidal diabase of the great copper-mining region of Lake Superior, where the metal is associated with these and other secondary minerals, including various zeolites. It is supposed that here the copper has * For a description of the rocks of this district see Sir Archibald Geikie's work : " The Ancient Volcanoes of Great Britain." London : 1897, vol. iv., p. 379. Caps. xxiv. and xxv. are devoted to a detailed description of ihe Carboniferous volcanic plateaux of Scotland. For a full description of the zeolites consult Mr. Goodchild' s paper cited above. f " The Scottish ores of Copper in their Geological Relations." Hep. Brit. Assoc., Glasgow, 1901, p. 647. 214 MINERALS OF SCOTLAND. been reduced from cupriferous solutions by the action of substances containing iron in the ferrous state, such as the augite and the magnetite of the eruptive matrix.* Senarmont showed long ago that copper-bearing solutions were readily reduced by being moderately heated with various oxidisable bodies. Possibly the formation of native copper in the narrow crevicea of rocks may receive illustration from Prof. BecquerePs experiments on electro-capillary action. He obtained deposits of metallic copper by allowing a cupric solution, like the nitrate, and a solution of sodium sulphide to react on each other by very slow diffusion in capillary spaces. f As metallic sulphides are rather uncommon in amygdaloidal rocks, the occurrence of the rare sulphide of cadmium, with prehnite, in the Carboniferous lavas of Renfrewshire, is peculiarly interesting. This compound, forming the species called Greenockite, is represented by Nos. 1518 to 1520 five specimens from the original locality near Bishopton. It was in piercing the hard rock to form the long tunnel at this part of the Glasgow and Greenock Railway that the mineral was originally brought to light. It was described as a new species by Prof. Jameson, who named it after Lord Greenock, after- wards Earl Cathcart (b. 1785, d. 1859) by whom it had been de- tected.J The crystals were measured by Mr. Brooke, and analysed by Prof. Connell. Greenockite, as seen in the specimens here exhibited, occurs in small sharply-defined hemimorphic crystals, referable to the hexagonal system, and presenting a yellow colour, inclining to orange, with a brilliant, rather adamantine lustre. The mineral was originally mistaken for zinc-blende. Sulphide of cadmium does indeed occur in certain kinds of blende known from the Bohemian locality as Przibramite ; and the two sulphides those of zinc and cadmium belong to an isodimorphous group. Hexagonal sulphide of zinc, in crystals much like those of Greenockite, constitutes the species distinguished by Friedel as Wurtzite. It is notable, too, that Sidot obtained zinc sulphide in hexagonal crystals by strongly heat- ing either the artificial amorphous sulphide or common blende.j] Si dot' s hexagonal blende is used for fluorescent screens in experiments on radio-activity. The specimens numbered 1521 to 1524 are excellent examples of the geodes formerly found in the andesitic lava so largely quarried as " whinstone " at the back of Gourock, near Greenock, in * " The Deposition of Copper by Solutions of Ferrous Salts." By II. C. Biddle. Journ. Geol., vol. ix. (1901), p. 430. t " Note sur les reductions metalliques dans les espaces capillaires," Comptes Rendus, vol. Ixxxii. (1876), p. 354. J " Notice of Greenockite, a new Mineral Species of the order Blende-." Ed. New. Phil. Journ., vol. xxviii. (1840), p. 390. " Chemical Examination of Greenockite, or sulphuret of Cadmium." By Arthur Connell. Ibid., p. 392. ||"Rcchcrchcs sur la cristallisation de quelques sulfures metalliques.'' Comptcs Rendus, t. Ixii. (1860), p. 999, . ZEOLITES, 215 Renfrewshire. These drusy cavities were lined with crystals of calcite, quartz and fluorite. It will be noted that some of the calcite is tinted pink. An analysis of the pink calcite of Gourock yielded Dr. Heddle 4 * 27 per cent, of manganous carbonate.* The fluor-spar occurs in dark purple cubes, seated on the calcite, and it has been remarked that of all minerals in these druses the fluor is the latest formed.f It is notable that fluor-spar, so common in many parts of England, is decidedly rare in Scotland. A rather extensive series of specimens, mostly from the Kilpatrick Hills (Nos. 1525 to 1552) illustrates the group of Zeolites, which are developed in exceptional beauty and variety in some of the Carboni- ferous lavas of the Clyde basin. The zeolites constitute a well- marked group of crystallised hydrated silicates, all containing aluminium, and most ot them likewise containing either cal- cium or sodium, or in some cases both. Usually the zeolites appear to be secondary products, resulting mostly, if not exclusively, from the alteration of various felspathic and felspathoid minerals, especially the lime -soda felspars. Some have indeed been regarded as hydrated plagioclase. Connected with the presence of water is the fact that these zeolites are softer and less dense than the felspars, their specific gravity being about 2*2. The zeolites are rather unstable minerals, and it is sometimes noticed that one species passes into another. It was observed by Cronstedt, in the early days of mineralogy, that most of these minerals intumesce when heated before the blow- pipe, whence they came to be called zeolites, or " boiling stones." They are readily decomposed by acids, and, as first noticed by Bergmann, many of them when so treated gelatinise. The condition in which the water occurs in the zeolites has been the subject of much discussion. In some cases it may occur partly as water of crystallisation and partly as hydroxyl belonging to the silicate molecule. The water of crystallisation appears to be very loosely held, being readily lost and regained, according to the dry- iicss or the humidity of the surrounding medium. With the loss of water, the optical properties of the mineral are affected. The de- hydrated zeolites may in certain cases be caused to absorb other substances than water, even various colouring agents, as shown by the experiments of Friedel. It is notable that certain zeolites occur in the red clays of the deep-sea floor, as described by Sir John Murray and the late Prof. Renard. Notwithstanding the low temperature prevailing in abyssal waters, certain chemical reactions go on, which result in the decomposition of the basic volcanic rocks by means of sea-water, and the formation of zeolitic minerals, like phillipsite. The origin of such minerals is therefore similar to that of the zeolites in amygdaloidal rocks, although the conditions of occurrence seem so * Trans. Roy. Soc., Edin., vol. xxvii. (1876), p. 499. f " Miscellaneous Notes on Chemical Geology." By Wallace Young. Trans. Geol. Soc. Glasgow, vol. iii. (1871), p, 3J . * 216 MINERALS OF SCOTLAND. different. Moreover Prof. Lacroix has shown that in the Pyrenees zeolitic minerals are in course of formation at the present day by the decomposition of rocks under the influence of water from melting snow.* Such an origin however, seems to be rather exceptional for the zeolites, and in most cases such minerals were probably formed at rather an elevated temperature. By prolonged action of thermal waters on the concrete at certain Roman stations in France, several species of zeolites have been pro- duced. Zeolites also occur in mineral-veins, especially in those which carry lead, with calcite in the gangue ; and their occurrence in the lead lodes of Strontian under these conditions has already been noticed (p. 211). It was shown by Wohler, in 1848, that powdered apophyllite is soluble in water, when heated in a closed tube to 180 C. ; and C. Doelter has since found that most zeolites dissolve in pure water, at temperatures between 120 and 160, whilst the solubility is still more marked when carbonic acid is present. On cooling, the zeolite separates from the solution in crystals. Sir A. Geikie believes that in many cases the amygdales, or mineral-kernels in lavas which were once vesicular, may have been deposited before the rock had completely cooled,f a view also held by Mr. Harker with regard to the zeolites of Skye .(p. 221). The mineral called Prehnite, of which a rather fine suite of speci- mens is here exhibited (Nos. 1525 to 1531), can hardly perhaps claim a place among the true zeolites, inasmuch as all the water seems to be basic, so that it is not strictly a hydrated silicate ; and further it is only slightly attacked by acids, whilst its hardness and density are greater than in typical zeolites. Nevertheless, it often occurs in association with the zeolites and was formed apparently under similar conditions, being found in amygdaloidal rocks, as well as in veins. It frequently forms botryoidal and mammillated masses, crystalline in structure, and usually of green colour, though sometimes brown. J The association of prehnite with copper is rather characteristic, and the brownish tint is sometimes referable to minutely disseminated particles of the native metal, whilst the green colour has been referred in some cases to the presence of chrysocolla, in others to chlorite or perhaps to epidote. Prehnite was a very common mineral at Boylestone Quarry in Renfrewshire, and at Bowling Quarry in Dumbartonshire. Associated with the prehnite, as shown by some of these speci- mens, there commonly occurs the zeolite called Thomsonite (Nos. 1532, 1533). This is a lime-soda silicate, generally in white or * " Sur la formation de zeolites sous 1' influence du ruissellement superticiel' ' Comptes Rendus, t. cxxiii. (1896), p. 761. f " The Ancient Volcanoes of Great Britain." Vol. ii., p. 189. The reference is here to the amygdaloidal rocks of Tertiary age. J The character of these curved aggregates of prchnite crystals lias been studied by Mr. Goodchild, in his paper on " The Natural History of the Scottish Zeolites,"' already quoted. ZEOLITES. 217 colourless crystals, of acicular or columnar habit, arranged in radia- ting groups. Among the other minerals exhibited here may be men- tioned the delicate fibrous zeolite known as mesolite (No. 1534). The commonest of the fibrous zeolites is termed natrolite ; and probably the- mineral known as galactite (Nos. 1535, 1536) is an isomorphous mixture of natrolite and scolecite, whilst the zeolite named crocalite (No. 1537) may also be regarded as a variety of natrolite. Of all the zeolites in this case the most attractive to the eye are the brick-red crystals of Stilbite (Nos. 1538 to 1541) and of Heulandite (Nos. 1542, 1544).* These two minerals have much in common. Both are lime-zeolites, apparently crystallising in the monoclinic system. The stilbite not infrequently occurs in sheaf -like aggre- gates of crystals, whilst the heulandite has quite a characteristic habit, the crystals being perhaps best described as coffin-shaped. The pearly lustre on the cleavage planes of the heulandite is worthy of notice. The red colour has been referred to the presence of included scaly crystals of gothite, or oxide of iron ; but Dr. Haugh- ton regarded the colour of some red heulandite which he examined as due to the molecular condition of the mineral. f Very notable is the specimen, No. 1540, showing the red stilbite embedded in a large cleavage rhombohedron of calcite, where the stilbite is obviously the mineral of earlier formation. " There may be some connection," says Mr. Goodchild, " between the colour of the stilbite and the lithological nature of the rock from which it has been derived." The brick-red minerals occur in the andesitic lavas of Stirlingshire and Dumbartonshire, and are labelled in most collec- tions as coming from the Campsie Hills.J The red heulandite has been also recorded from Little Cumbrae. But little need be said about the other zeolites shown here. Analcite, or Analcime (No. 1548), is exceptional among zeolites in its crystallisation, inasmuch as it occurs in icositetrahedra, resembling those of leucite a mineral to which it seems to be related. The crystals of analcite are remarkable for their optical behaviour. The mineral called Cluthalite (No. 1545) is perhaps an altered analcite. Chabazite (No. 1546) occurs well crystallised in rhombodehra, which have a cube-like appearance, rather suggestive of crystals of fluor. Twin crystals are not infrequent. The most unstable of all the zeolites is the efflorescent mineral which received the name of Laumontite (No. 1547) after an old French mineralogist, Gillet de * The mineral here called stilbite is termed by many Continenta. 1 mineral- ogists Desmine, whilst our heulandite is often known as Stilbite. Some of the zeolites described above as "apparently monoclinic" may really be anorthic. f Journ. GeoL Soc., Dublin, vol. viii. (1860), p. 234. J See " On New Localities for Zeolites." By Prof. M. Forster Heddle. Trans. GeoL Soc. Glasgow, vol. ix. (1893), p. 72. The author failed to find them in the Campsie Hills. " A visit to the Island of Little Cumbrae, with some notes on its Miner- als." By James Neilson. Ibid., p. 373. 7882. ^ 218 MINERALS OF SCOTLAND. Laumont. Edingtonite (No. 1549) is rather notable inasmuch as it contains barium, and to this extent bears some relation to the zeolites already described as harmotome and brewsterite (p. 211). Several specimens of Pectolite are here exhibited (Nos. 1550 to 1552). This mineral can hardly be regarded as a true zeolite, yet it occurs under very similar conditions, being often found as a secondary mineral in the vapour-vesicles or in the fissures of old basic lavas. It generally forms tough, radiated masses, composed of fibres which are often silky in lustre. In certain cases it is pseudomorphous after analcite. Some of the specimens, of rather greenish-grey colour, are from the Ratho quarries, near Edinburgh, and have hence been described under the name of Ratholite. They occur in an intrusive sheet of dolerite, in the Lower Carboniferous strata. Following the zeolitic group of minerals comes a small series illustrating the characters of Scottish agates. (Nos. 1553 to 1560). Like zeolites, the agates occur usually in the steam cavities of eruptive rocks, as secondary minerals resulting from the decomposi- tion of the matrix ; like zeolites, again, they occur occasionally in veins. In Scotland the best agates are derived from the andesitic lavas of the Lower Old Red Sandstone ; and Mr. Goodchild has re- marked that since they occur in the conglomerate of the Upper Old Red Sandstone, some at least must have been formed within the limits of time represented by these rocks. On the disintegration of the matrix the agates may weather out, and be found loose in the soil as " Scotch pebbles." The polished sections of pebbles, Nos. 1553 to 1557, are from near Montrose. An agate consists of alternating layers of various siliceous minerals, especially chalcedony, but including also cachalong, quartz and opal . These minerals have been deposited from siliceous solutions, which gained access to cavities in the old lava. It generally happens that the walls of the cavities are immediately lined by a deposit of the green earthy minerals known as celadonite and dekssite minerals which have resulted from the decomposition of augite, or some other ferro-magnesian mineral in the eruptive rock. Upon this " priming," to borrow Mr. Goodchild's expressive term, the chalce- dony may be deposited either directly or with an intervening layer, which, according to Dr. Heddle, may be zeolitic. Gelatinous silica was deposited in the interior of the cavities, in most cases equally around the whole internal space, the material having secured adhesion to roof and wall as well as to the floor. Successive de- posits, more or less variable in character, were thrown down in regu- ] ar sequence, layer upon layer, so that a transverse section of an agate displays a zonal pattern due to the cut edges of the deposits. Many agates exhibit tubular orifices or cracks which appear to have served as channels for the passage of the siliceous solutions. They were formerly regarded as inlets of infiltration, but G. Lange many years ago suggested that they might be channels of egress, through which the solution, after deposition of more or less of its siliceous burden, had been expelled. Dr. Heddle, who made a MINERALS OF THE HIGHLANDS. 219 special study of agates, also regarded these channels as " tubes of escape," believing that the solution from which the silica had been precipitated passed out on the introduction of a stronger solution, by osmotic action.* In some cases, as seen in No. 1556, the siliceous minerals may form horizontal deposits on the floor of the cavity, producing an onyx\ in other cases the deposits may hang from the roof of the cavity as stalactitic chalcedony ; or they may be deposited over and around rugosities of the walls and floors, forming concentric deposits, circular on section, known as eye agate. In the tray No. 1558 are two eye-agates from the Path of Condie in Perthshire ; No. 1559 is a specimen of moss-agate from Dunbar, and No. 1560 a polished slab of red jasper from Campsie Glen. A large collection of polished specimens of Scottish agates and jaspers will be found in Sections P. and 4> of the Horse-shoe Case ; and hence it has not been deemed necessary to exhibit a large number here. The Ludlam collection was far from rich in examples of such minerals. MINERALS OF THE HIGHLANDS. (Nos. 1561 to 1572.) For convenience of space the minerals from the lead-mines of Strontian, in Argyllshire, have been placed in Case XI., in juxta- position with the ores of the Leadhills district. Comparatively few other minerals from the Highlands of Scotland are exhibited in this collection. The specimens numbered 1561 and 1562 are good examples of the red variety of epidote, named by Sir David Brewster, \Yithamite.-f This mineral occurs in the altered lavas of the Lower Old Red Sandstone of Glencoe, in Argyllshire, where it was first detected in 1824 by Henry Witham. Brewster observed its remarkable dichroism ; and in recent years its optical characters have been fully studied by Prof. Lacroix, who has pointed out their relation to those of epidote and piedmontite the latter a manganese -epidote. J Dr. Heddle found in the Withamite of Glencoe 0'138 per cent, of manganous oxide. According to Mr. Goodcbild the mineral has resulted from the alteration of celadonite, itself probably due to the decomposition of the pyroxene of the eruptive rock in which it occurs. Withamite has recently been found by Mr. Muff, of the Geological Survey, in a dyke at the Meeting of the Three Waters. || * On Scottish agates see Dr. Heddle' s paper " On the Structure of Agates." Trans. Geol. Soc., Glasgow, vol. xi., part ii. (1900), p. 153 ; also his " Miner- alogy of Scotland," vol. i. p. 58 ; and Mr. Goodchild's paper " On the Genesis of some Scottish Minerals.'' Proc. Phys. Soc., Edin., vol. xiv. (1899), p. 191. f " Description of Withamite, a new mineral species found in Glencoe. " Edin. Journ. Sc., vol. ii. (1825), p. 218. | " Proprietes optiques de la Withamite." Bull. Soc. Min. JPr, vol. \x. (1886), p. 75. " Minerals new to Britain." Min. Mag., vol. v. (1884), p. 15. || " Summary of Progress " for 1903, p. 55. 7882. q 2 220 MINERALS OF SCOTLAND. The great granite masses of the Central Highlands have yielded a few notable minerals, such as the well-known Cuirnyorni. This is a variety of quartz, of smoky or yellow tint, named after the mountain in Banffshire, where it occurs in drusy cavities in veins of granite running through the main mass. In order to obtain the cairngorm, pits were formerly dug in the disintegrated part of the granite, and the mineral was found as loose crystals in the kaolinised material. Rolled crystals occurred in the bed of the River Avon. As Mr. Cunningham Craig remarks, the veins represent intrusions of the acid magma into fissures of contraction in the granite, and the quartz has probably crystallized from highly siliceous solutions which filled the cavities in the veins.* In addition to the specimens shown here (Nos. 1505 to 1568), a fine series of cairngorms, including many cut specimens of great beauty, will be found in Section N. of the Horse-shoe Case. It should be noted that brown and yellow quartz is sometimes im- properly called " topaz," or i( smoky topaz," a practice not uncommon in trade and even in scientific writings. The fine specimen of smoky quartz, No. 1568, presented by G. Barrow, Esq., is from Banchory in Aberdeenshire. Associated with the smoky quartz of the Cairngorm district, and occasionally occurring in the bed of the Avon, were formerly found crystals of true Topaz. Some of the largest have been obtained from Benabourd (Beinn a' Bhuird), in the Aberdeenshire part of the granite mountains, whence several specimens, each more than a pound in weight, have been recorded. The collection includes some excellent examples of Scottish topaz (Nos. 1569 to 1572), illustrating the crystalline forms, the characteristic basal cleavage and the typical tints of the mineral. Most of the specimens are of pale blue colour, inclining in certain parts to a reddish brown tint, whilst some are practically colourless. Beryl occasionally accom- panies the topaz of the granite of the Grampians, as is the case in so many other localities. Reference has already been made (p. 25) to the probable origin of topaz in granitic rocks by pneumatolytic action. Two specimens of Rutile, the most common of the three species of titanium dioxide, are here exhibited. This mineral not in- frequently occurs in quartz veins in the crystalline schists. No. 1563 from Killin, in Perthshire, shows the rutile in reddish-brown acicular crystals penetrating quartz ; whilst in No. 1564 it occurs as a stout prismatic crystal, longitudinally striated, associated with muscovite and quartz. It is notable that in the latter specimen the crystal has been bent and broken, and the fragments cemented together by quartz. Prisms of tourmaline sometimes exhibit similar fracture and cementation. Brief reference may here be made to the recent discovery, by the Geological Survey, of Cassiterite in the granite gneiss * " On Cairngorms."- By E. H. Cunningham Craig, B.A. Rep. Ass., Glasgow, 1901, p. 654. ZEOLITES. 221 oi Cam Chuinneag in Ross-shire.* The discovery is of special interest, inasmuch as tin- stone, though found in England and Ireland, had not previously been known to octfur in Scotland. It is notable that the cassiterite is here found under exceptional conditions, being associated with much magnetite but without tourmaline, and with but little quartz. The mode of occurrence is at present (1904) fully illustrated in a table case, placed near the collection of Scottish Minerals. MINERALS OP THE WESTERN ISLES, ETC. (Nos< 1573 to 1584.) Many of the basic lavas of Tertiary age, which occur in the Western Isles of Scotland, spreading out as extensive plateaux or rising into tabular hills, enclose in their vesicular cavities a number of zeolitic minerals similar to those already described as occurring in the older volcanic rocks of the Midland Valley. Such minerals are represented here by a small suite of characteristic specimens from the Isle of Skye, principally from the rocks of Storr, in the northern part of the island. According to Mr. Harker, who has made an elaborate study of the Tertiary igneous rocks of Skye, the minerals of the amygdaloidal basalts were formed from the alteration of the rocks not by ordinary weathering but by the action of heated water, probably of volcanic origin, soon after the extrusion of the lava : indeed, their formation may represent the final phase of volcanic activity.! It is interesting to note that, by thermal metamorphism, the zeolites have in some cases been transformed to felspar apparently a reversion to their original condition, due chiefly to loss of water. Among the zeolites of Skye here exhibited are specimens of StUbite (Nos, 1573 to 1576), showing the mineral in white crystals, with pearly lustre on the cleavage faces, the crystals being, in some cases, aggregated in sheaf-like groups, and in others displayed in radiating forms. Laumontite is illustrated by No. 1577, where the white efflorescent mineral is partly coating crystals of stilbite. No. 1578 is a specimen of Chabazite, in which the mineral is seen in white rhombohedral crystals, rather recalling the general aspect of fluor- spar. Analcite, or Ancdcime, is represented by No. 1579, which shows the sharply defined white icositetrahedral crystals so charac- teristic of this species. According to Dr. Heddle the form in the Tertiary traps of the Hebrides is invariably the simple icositetra- hedron, whilst in the palaeozoic lavas of Scotland the species some- times shows faces of the cube. { * " Summary of Progress " for 1903, p. 58. t Mem. GeoL Surv., " The Tertiary Igneous Rocks of Skye." By Alfred Flarker, M.A., F.R.S., with Notes by C. T. dough, M.A., 1904. 1 " On Analcime with New Forms." Trans. Edin. Geol. Soc., vol. vii. (1899), p. 241. Also " Mineralogy of Scotland," vol ii., p. 103. 222 FUNERALS OF SCOTLAND AND IRELAND. No. 1580 is a specimen of Mesolite, in which white needle-like crystals spring from the walls of a drusy cavity in basalt, 'whilst No. 1581 is an example of the lime zeolite known as Gyrolite. With the zeolites, though perhaps in strictness hardly belonging to the group, is placed an example of Pectolite (No. 1582), a mineral of which a brief notice has already been given (p. 218). The specimen of CMorophceite (No. 1583) is in an amygdaloidal basalt from the Isle of Rum. This mineral appears to be a hydra ted basic silicate of iron, magnesium and calcium, derived from the decomposition of the ferro-magesian silicates in the lavas, and forming in their vesicular cavities an amorphous substance of dark green, or in some cases almost black colour. The series of Scottish minerals is brought to a close by a speci- men of Chromite or chromic iron-ore (No. 1584) from Unst, one of the Sheltand Islands, where it occurs in a matrix of serpentine. This mineral, which is a member of the ' spinel group ' and is rather variable in composition, has been worked commercially in Shetland as a source of chromium and its compounds. The chromite probably became segregated from a basic eruptive magma, through which it was originally diffused. DIVISION 2. MINERALS OF IRELAND. MINERALS OF LEINSTER. (Nos. 1585 to 1600.) The collection of Irish minerals, though not large, is fairly representative, and gives within narrow limits a general notion of the mineralogy of Ireland. According to Mr. H. J. Seymour,* the number of mineral species known to occur in Ireland is abou 115. In the arrangement of this Collection, the minerals of each of the four provinces are grouped together. For a concise description of the geology of Ireland, the visitor may be referred to the Guide to the Survey Collections in the Dublin Museum of Science and Art.")' Among the minerals of Leinster the most interesting are the specimens of Native Gold from Croghan Kinshelagh, in County Wicklow (Nos. 1585 to 1587). This mountain is part of an elevated tract rising to a height of 1987 feet above sea-level, and consisting mainly of slaty rocks of Lower Silurian (Ordovician) age, associated * " Preliminary List of the Minerals occurring in Ireland.'- By Henry J. Seymour, B.A. ~Rep. Brit. Assoc., Belfast, 1902, p. 598. Also Supplementary List in Rep. Brit. Assoc., Southport, 1903, p. 671. t ;i Guide to the Collections of Rocks and Fossils belonging to the Geo- logical Survey of Ireland.'- By A. McHenry, M.R.I.A., and W. W. Watts, M. A., Dublin, 1898 WlCKLOW GOLD. 223 with intruded masses of certain eruptive rocks. The gold occurred in the valley gravel of several streams, principally in that of the Gold Mines River.* It has been suggested that the alluvial deposits of this district probably supplied much of the gold used in the ancient Keltic ornaments of Ireland. In modern times attention was prominently directed to the Wicklow area by the accidental discovery of gold there in the year 1795. Crowds of peasants were attracted to the diggings, and it is said that gold to the value of several thousand pounds was obtained by desultory working, before the Government commenced systematic exploration.f The official workings were discontinued at the outbreak of the Rebellion in 1798, but were renewed in 1801, when tunnels were driven into the mountain, in quest of the quartz reefs, which were supposed to have supplied the detrital gold ; but these explorations were unattended with success. The largest nugget ever found in the Wicklow workings, repre- sented by a model in Wall-case 14, reached the weight of about 22 ounces. Its remarkable story was told by the late Prof. V. Ball. J The specimens in the Case under description include several samples of the alluvial gold, of which No. 1587 is peculiarly interest- ing, inasmuch as it shows the metal in a water- worn pebble of iron- stained quartz, and consequently indicates the nature of the original matrix. The alluvial gold of Wicklow was associated with magnetitt, and to a less extent with cassiterite and wolfram, thus recalling the conditions under which gold occurs in Cornwall. Other minerals were also occasionally found, such as molybdenite, galena, chal- copyrite, corundum, zircon and spinel, whilst the existence of platinum, though not definitely proved, was suspected. The origin of the minerals was probably connected with the intrusion of the eruptive rocks into the slates. || No. 1588 is a specimen of granular magnetite from Bally coog, in County Wicklow, where workings were at one time carried on to a limited extent upon veins of this mineral, coursing through the slaty rocks of the district. The mineral deposits of Wicklow, although yielding but little at the present time, have been in their day more important than * For the geological structure of the district, and for bibliography relating to the Wicklow gold mines see " Explanatory Memoir to accompany sheets 138 and 139 of the Geological Survey of Ireland." By Edward Hull, LL.D., F.R.S. 1888. t The workings formed the subject of a comic opera, played at Co vent Garden under the title of " The Lad o' the Hills ; or the Wicklow Gold Mines." J " On the gold nuggets hitherto found in the County Wicklow." Sci. Proc. Roy. Dublin 8oc. (new series), vol. viii. (1895), p. 311. " On the Minerals of the Auriferous Districts of Wicklow." By William Mallet, Esq. Journ. Geol. floe.., Dublin, vol. iv. (1851), p. 269. || For the occurrence of Irish gold see paper by the late Gerrard A. Kin- ahan *' On the mode of occurrence and winning of gold in Ireland. 3 ' Sci. Proc. R. Dub. Soc. (ii.s.) vol. iii. (188&), p. 263. 224 MINERALS OF IRELAND. those of any other county in Ireland. The metalliferous minerals including ores of iron, copper and silver-lead are confined chiefly to a great band, or "mineral channel," stretching from Wicklow in a south-westerly direction to Ovoca, and thence to Croghan Kinshelagh, a distance of fourteen or fifteen miles.* The ore now worked is for the most part iron-pyrites, known generally as Sulphur- ore. Previously to about the year 1840 the pyritic deposits of Ovoca were not worked for sake of their sulphur, but some of the ore-bodies were wrought as copper-mines. Much of the pyrites, indeed, contains a small proportion of copper, thus resembling the cupriferous pyrites which occurs in enormous deposits in Spain and Portugal, In recent years most of the Irish ore has been beaten out of the market by Spanish pyrites. No. 1589 is a specimen of copper- bearing pyrites from Ballymurtagh Mine, in the Vale of Ovoca. In the year 1902 the mines of Wicklow yielded 1,617 tons of pyrites, or " sulphur-ore," and 444 tons of cupreous pyrites, containing about 2 per cent, of copper. In addition to the copper in the iron pyrites, copper also occurs to a limited extent, as chalcopyrite, forming distinct " bunches " of ore : black copper ore, consisting chiefly of the oxide, was formerly found in the shallow workings, sometimes in workable quantity, and native copper was not unknown. Large quantities of copper precipitate were formerly produced at the Ovoca Mines, by means of scrap-iron which effected the reduction of the metal from the coppery water that drained through the pyritic deposits. The process was similar to that already noticed in connection with the production of " cement copper " in Anglesea (p. 127), An interesting historical account of the precipitation processes, as carried on in Ireland and on the Continent, will be found in the late Sir Warington Smyth's memoir on the mines of Wicklow.f Although no lead- ore is now worked in Wicklow, this mineral was formerly the object of extensive exploration in certain parts of the county. No. 1590 is a sample of galena crystallised on quartz, from the old Luganure mines at Glendalough. The lodes yield- ing the lead- ores of this district run through granite, in a direction nearly north and south. Some of the other lead veins, as at Glenmalure, occur near the junction of the granite with the neighbouring mica-schist. A specimen of green pyromorphite from Glenmalure is here shown (No. 1593), and there are also two specimens of cerussite (Nos. 1591 and 1592), in further illustration of the secondary ores of lead. Both specimens show the cerussite * For a description of the metalliferous minerals of Ireland, see Mr. G. H. Kinahan's comprehensive paper on " Irish Metal Mining " in Scient. Proc. Boy. Dublin Soc., new series, vol. v. (1886), pp. 200-317. t " On the mines of Wicklow and Waterford." Records of the School of Mines, vol. i, part iii. (18.53), pp. 349-412. See also " Notes on the Recovery of Copper from its solution in mine drainage, with special reference to the Wicklow Mines." By Philip Argall and Gerrard A. Kinahan. 8c. Proc. Roy Dub. Soc , new series, vol. iii. (1883), pp. 302-328. MINERALS OF LEINSTER. in good crystals, and in No. 1592 these crystals are seated on a matrix of decomposed galena, clearly suggesting the origin of the carbonate as an alteration- product of the original ore. Professor J. Joly has recorded the occurrence of harmotome in the gangue of the Luganure lode, where also fluor-spar, barytes, and strontianite occur, associated with galena, blende, pyrite and copper pyrites.* The mineral called KUmacooite, represented by No. 1595, is a mixed sulphide, much resembling the so-called " blue-stone " of Anglesea. It has been regarded as an intimate mixture of galena and blende, and described by Dr. Tichborne as " an argentiferous galenitic-blende." f It generally contains, however, not only the sulphides of lead and zinc, but, also subordinately, and in variable proportion, those of iron, copper and antimony, with silver to the extent in some cases of eight ounces to the ton. Large quantities of the mineral were raised from the Kilmacoo lode, in the Connary Mine. According to Mr. Argall, the iron-pyrites in the main lode at the Magpie Mine graduated locally into kilmacooite.J The great mass of Leinster granite has yielded some interesting minerals, but these are scarcely represented in this Collection. The tray numbered 1596 contains some beautiful crystals of transparent quartz, of a delicate smoky tint, presenting the form which has led to its name of Sceptre quartz. In such crystals, which are found near Carlow, a slender six-sided prism is expanded towards the summit so as to pass into a stouter prism, which is capped by the hexagonal pyramid. No. 1598 is an example of plumose mica, from near Dublin, showing the silvery muscovite gracefully spread out in feather-like forms. The mineral named Killinite, from Killiney Hill, south of Dublin, where it was discovered in 1817, is represented by the specimen No. 1597. This mineral appears to have resulted from the alteration of spodumene, a species which is known to occur in the granite. According to the late Dr. Haughton " the so-called Killinite is an altered spodumene, from which the litliia has been washed out by weathering." It has long been known that Beryl occurs in the Leinster granite, and it has been found by Prof. Joly in the quarries of Glennullen, County Dublin.ll *" On the occurrence of Harmotome at Glendalough, County Wicklow."' By J. Joly, B.E. Sc. Proc. Roy. Dub. Soc., new series, vol. v. (1886), p ? 165. t " On an argentiferous galenitic-blende at Ovoca." By C. R. C. Tich- borne, LL.D. Ibid., new series, vol. iv. (1885), p. 300. J " Notes on the Ancient and Recent Mining operations in the East Ovoca District." By P. H. Argall. Ibid., new series, vol. ii. (1880), p. 211. " On the Mineralogy of the counties of Dublin and Wioklow." By the Rev. Samuel Haughton, M.D. Journ. Roy. Geol. Soc. Irel., new series, vol. v., part iii. (1880), p. 43. See also Dr. Galbraith's paper " On the different analyses of Killinite. "- Journ. GeoL Soc. Dub., vol. vi. (1856), p. 165. || " Notes on the Minerals of the Dublin and Wicklow granite."- By J. Joly. B.E. Sc. Proc. Roy. Dub. Soc., new series, vol. v. (188(>), p. 48. See also Prof. J. R O'Reilly in Journ. R. GeoL Soc. Irel. (n.s.), vol. vii. (1887), p. 69. 226 MINERALS Of IRELAND. MINERALS OF CONNAUGHT. (#os. 1599 to 1604.) Among the ores which have been worked from time to time in this province, those of iron from the Connaught coalfield are perhaps the most important ; but these ores are not at present represented in the Collection. Ores of lead and copper have occasionally been the object of ex- ploration in Galway, where lodes and other ore-deposits occur in the granitic and metamorphic rocks as well as in the Carboniferous Limestone. No. 1599 is a specimen of copper -pyrites from the Cregg Mine, in Oughterard. According to the Survey Memoir, by Mr. G. H. Kinahan, the mineral occurred in a strong lode bearing N. 66 W. and hading to the south.* No. 1600 is a cleavage-piece of galena, boldly crystalline in structure, from the neighbouring mine of Clooshgereen, which was worked on a continuation of the Cregg lode. Barytes occurs with the lead ore at the Cloosh Mine, and is represented by two samples : in one of these, No. 1601, the mineral forms a snow-white crystalline mass, and in the other, No. 1602, it presents a translucent glassy appearance, with well-marked cleavage- planes. The specimen No. 1602 was presented by H. E. A. Young, Esq., whilst Nos. 1601 and 1602 were the gift of J. T. Darke, Esq, In the year 1902 the province of Connaught yielded 463 tons of barytes, but this was raised in County Sligo. Large deposits of the mineral occur in the King's Mountain. It is notable that Native Sulphur, quite a rare mineral in Britain, occurs in the Carboniferous Limestone of Oughterard. No. 1603 is an excellent specimen of this sulphur, in its matrix, contributed by the Geological Survey of Ireland. The sulphur occurs, in associa- tion with calcite and pearl-spar, lining geodes or drusy cavities in the limestone, and is occasionally found inside fossil shells. Mr. Kinahan has suggested that the sulphur of Oughterard may have been known in ancient times, since a river at this locality is named Owenrift a word which means in English " Brimstone River."f Native sulphur may owe its origin, in many cases, to reduction from various sulphates, especially from gypsum, as already men- tioned in connection with specimens from Nottinghamshire (p. 185). It may also be reduced from metallic sulphides, like pyrites and galena. Then again, natural waters, especially thermal springs, may contain sulphides, from which sulphur will be precipitated on exposure to the air, the deposition being facilitated by the action of carbonic acid and by organic agencies like bacteria. Among the few Connaught minerals here exhibited is a specimen of RutUe (No. 1604) from the mica-schist of Cush-cum-Curragh, near Borrishdale, on the north of Clew Bay in County Mayo. This *M?.m. GeoL flurv. Ireland,. Explanation of Sheet 105 and part of Sheet 114. By G. H. Kinahan. 186fl. p. 58. t Mem. Oeol. Surv. Ireland. Explanation of Sheet 95. By G. H. Kinahan and J. Nolan, 1870, p. 63. MINERALS OF ULSTER* 227 specimen was presented by Spencer G. Perceval, Esq., by whom the mineral was discovered at this locality in 1868. It occurs in prismatic brown crystals, with vertical striations and other typical characteristics. The mineral was analysed by Prof. Emerson Reynolds, who noted the occurrence with it of small black crystals of the variety of rutile distinguished as nigrine* MINERALS OF ULSTER. (Nos. 1605 to 1633.) Several groups of minerals from different parts of the province of Ulster are exhibited in this Division of the collection. One small but interesting group represents certain minerals from the granites and crystalline schists of the highlands of Donegal. Among these the specimens of Beryl are especially noteworthy. According to Mr. R. H. Scott,f beryl occurs as an accessory mineral disseminated through part of the granite as well as in veins of quartz running along the joints. The large crystals of beryl exhibited here were obtained from Sheskinaroan, a little to the north of Dungloe, on the road to Anagary. One of the specimens, No. 1605, shows a six-sided prism of opaque white colour, in a matrix of pegmatite ; whilst in the tray, No. 1608, are two specimens of beryl, more or less greenish in colour, and embedded in quartz. The Donegal beryl was analysed by Dr. Haughton.J: By side of the beryls are exhibited several large crystals of Garnet. The garnets of Donegal occur both in crystalline schists and in altered limestone. The tray, No. 1609, contains two large brown rhombic dodecahedra, more or less eroded on the surface, and referable to the common species generally known as Andradite. Mr. Scott refers to loose crystals, frequently two inches in diameter, pitted by the action of sea-water, occurring on the beach at Tober- keen. In No. 1610 the garnet is associated with Idocrase, or Vesuvian, in brown bacillary forms. Such an association is by no means uncommon, especially in the contact-zone between limestone and crystalline rocks. Epidote and wollastonite occur in Donegal under similar conditions. The minerals exhibited here from the highlands of Donegal were obtained some forty years ago by Patrick Doran, a well-known collector who visited the wildest parts of Ireland in quest of minerals, and contributed materially to our knowledge of Irish mineralogy. In addition to these there is a specimen of Cyanite (No. 1611), from County Donegal, presented by J. Rhodes, Esq. *" Note on Specimens of Rutile, from the County Mayo." By J. Emerson Reynolds. Journ. Roy. GeoL Soc. Dublin, new series, vol. ii. (1871), p. 164. j- " On the Mineral Localities of Donegal."- Journ. Roy. Dub. Soc., vol. iv. (1866), p. 114 ; Rep. Brit. Assoc., for 1863, p. 67. 1 Quart. Journ. Geol. Soc-., vol. xviii. (1862), p. 417 ; Rep. Brit. Assoc., Neweastle-upon-Tyne, 1863, p. 58. For a geological description of N.W. and Central Donegal, see Mem. leol. Swu. Ird. to accompany Sheets 3, 4, 5, 9, 10, 11, 15 and 16, 1891. 228 MINERALS OF IRELAND. Another group of interesting minerals from a granitic district in Ulster is illustrated by the specimens here exhibited from the Mourne Mountains in County Down. This granite is especially interest- ing to collectors of minerals inasmuch as it presents in marked degree a miarolitic structure, that is it contains numerous cavities which are lined with crystals of the constituent minerals. It is from these druses that the specimens here exhibited have been obtained. According to Prof. Sollas the granite of the Mourne Mountains is in all probability of Tertiary age* a view supported by other geologists. In No. 1612 a drusy cavity contains rather large crystals of orthodase associated with sharply denned crystals of smoky quartz, and with a dark mica. The granite of the Mourne Mountains contains also albite, or soda-felspar, as first pointed out by Dr. Haughton. In some of this granite the quartz, contrary to its usual habit, has consolidated before the felspar. Among the accessory minerals of the granite, topaz and beryl occasionally occur as crystals studding the walls of the cavities. A beautiful crystal of colourless Topaz, of characteristic prismatic habit, is seen in No. 1616 ; whilst excellent crystals of Beryl will be found in the trays, Nos. 1613, 1614 and 1615. One of the beryls presents the form of a rather clear green prism, without the terminal plane ; in another specimen the sea-green crystal shows the hexagonal prism combined with the basal pinacoid ; whilst in a third specimen the prismatic crystal is opaque and fractured. The Irish beryls are further represented by three isolated crystals of blue colour, sufficiently clear to be cut as ornamental stones. These are in the tray, No. 1615. One of these is a magnificent crystal, presenting the form of a striated six-sided prism measuring two inches in length, translucent and bright blue at one end, but be- coming white, dull and opaque towards the base. The basal plane is rough and is coated with a little oxide of iron. Transparent beryl, when of a bluish-green colour is known as Aquamarine. A special group of minerals is yielded by the Tertiary volcanic rocks of the north-east of Ireland. These rocks are mostly basalts and dolerites, in many cases amygdaloidal, and containing zeolitic minerals of much beauty, closely resembling those of the Western Isles of Scotland. Prominent among the zeolites here exhibited are the specimens of Analcite or analdme (Nos. 1617 to 1619), mostly in dead white icositetrahedral crystals. In the specimen, No. 1619, however, the little sharply defined crystals are translucent or trans- parent, and are seated on " wacke," or decomposed trap-rock, from Benyevenagh. " It is an interesting fact," wrote Colonel Portlock in reference to the Irish analcime, " that the transparent varieties are invariably of a lower degree of hardness than the more opaque."-)- * " Preliminary Observations on the Granites of Wicklow and Down."- Scien. Proc. Roy. Dub. Sac., new series, vol. vi. (1888), p. 257. t " Report on the Geology of the County of Londonderry, and of parts of Tyrone and Fermanagh." Dublin, 18 13, p. 220. MINERALS OF ANTRIM. 229 One of the commonest of the Ulster zeolites is Natrolite (Nos.1621, 1622) a mineral which usually occurs in delicate white needle-like crystals, shooting across the cavities of the vesicular lava. Among the other so-called " basaltic minerals " mention may be made of Antrimolite (No. 1625) one of Dr. Thomson's numerous " species " now regarded as a variety of mesolite. The specimen shows the antrimolite from the Giant's Causeway in white botryoidal masses, of radio-fibrous structure. The Levyne (No. 1620), named by Sir D. Brewster after Levy who made the catalogue of the Turner collection, seems to be a variety of chabazite, though much dis- cussion has arisen with regard to its true relationship. Gyr elite, of which No. 1623 is a specimen, is a zeolite regarded by some as an altered form of apophyllite. The dark green mineral in the basalt, No. 1626, is Thomson's Kirwanite a mineral which has perhaps resulted from the decom- position of the augitic constituent of the rock, and seems to be re- lated to the group of rather ill-defined substances known as " green earth." No. 1627 is a specimen of basalt from the Isle of Muck, near Magee Island, of! the east coast of Antrim, showing well-defined octahedral crystals of magnetite coated with brown oxide of iron. Even larger octahedra are seen on the fine specimen from Magee Island, No. 1628. At the present day the iron-ores of Antrim are the most important minerals raised in Ireland. * In the year 1902 the county yielded as much as 81,612 tons of ore. The " iron-ore measures " are an irregular series of iron oxides with clays and lignites, associated with volcanic tuffs, intercalated between the upper and lower groups of basalts and dolerites. Thin beds of bole, or ferruginous clay, resulting from the atmospheric disintegration of the volcanic rocks, occur between the successive lava flows at various horizons, especially in the Lower Basalts, but the great group of iron-bearing minerals, with the associated lignites and clays, forms a definite zone, probably of lacustrine origin, representing deposits in sheets of shallow water on the exposed surface of the older set of lava- flows. The richest ore is known from its structure, as pisolitic iron- ore, or pebble ore (No. 1629).f This is composed of small concretions of limonite or haematite, embedded in a matrix of ochreous clay. Somewhat similar concretionary ores are in course of formation at the present day at the bottom of certain lakes, especially in Sweden, * See Mem. Geol. Surv. Explanatory Memoir, Sheets 21, 28 and 29 (Ire- land). By Edward Hull, M.A., F.R.S. (1876.) Also, Sheet 20. By R. Glascott Symes, M.A. (1886), and Sheet 19. By R. G. Symes and Alexander McHenry (1886). fSee " Notes on some of the Irish Crystalline Iron-Ores." By G. H. Kinahan. Sc. Proc. Roy. Dubl. Soc., new series, vol. iv. (18S5), p. 306 ; also " Notes on the Tertiary Iron-Ore Measures, Glenariff Valley, County Antrim."- By Philip Argall. Journ. Roy. Geol. Soc., Ireland, new series, vol. vi. (1886), p. 98 ; am} in Sc. Proc. Roy. Dublin Soc., new series, vol. iii. (1883), p. 15],. 230 MINERALS OF IRELAND. where the deposition of the iron-oxide seems to be determined by the play of organic activities, whilst the ultimate source of the iron is probably referable to the decomposition of pyrites or of various iron-silicates in the crystalline rocks. In the substance known as Belfast aluminous ore (No. 1630) the oxide of iron is associated with much alumina uncombined with silica, and the substance has thus acquired value as a fluxing agent in the reduction of siliceous ores, like certain kinds of haematite. It is sometimes regarded as a kind of bole. Aluminium hydroxide, in which iron replaces aluminium to a greater or less extent, is often termed Bauxite, from Les Beaux, a locality near Tarascon in the south of France ; but the name has been used rather loosely and extended to various mineral substances, some of which pass into ferruginous clays. Bauxite is used in the preparation of aluminium and its salts. In the year 1902 the Irish bauxite (No. 1631) was raised to the extent of 9,047 tons. Alumina is prepared from this material at the works near Larne, and is sent thence to Foyers, in Inverness- shire, where it is reduced to the metallic state in the electric furnace.* Some of the so-called bauxite of Antrim has been known as alum day, but the proportion of silica is sometimes extremely low. Titanic oxide exists, however, to the extent of about 2 per cent. No. 1632 is a sample of the ferriferous clay known as lithomarge, which occurs with the iron-ore measures, and here presents the appearance of a speckled purple rock. The " pavement " is the name given locally to a poor kind of ore, on which the richer ore rests. At the Evishnably Mine the pisolitic ore yielded 35 to 40 per cent, of iron ; the pavement about 28 per cent, and the violet lithomarge about 17 per cent.f On the evidence of the vegetable remains preserved in certain leaf- beds between the Upper and the Lower basalts, it is inferred that the volcanic outbursts in the Antrim plateau go back to Oligocene or even to late Eocene time. The iron-ore measures seem to represent the denudation of the volcanic rocks during a pro- longed pause - between the earlier and the later episodes of volcanic activity. Superficial deposits of bog iron-ore are found in various parts of Ulster, and the substance has in some cases been worked for use in the purification of coal-gas. The ore is an impure limonite, formed partly by organic agency. Strata of Triassic age occur in County Antrim, and here as else- where the Keuper marls contain rock salt and gypsum. No. 1633 is a specimen of clear colourless crystalline salt, or Halite, from Maiden Mount Mine, near Carrickfergus. It appears that salt was first discovered in Antrim, while sinking for coal in 1850. At the present time the salt-measures are rather extensively worked * " Mineral Statistics " for 1902, p. 172. t Mem. Geol. Surv. Memoir to accompany Sheet 20, Ireland. By R. GJascott Symes, M.A. (1886), p. 12. MINERALS OF MUNSTETt. 231 in the neighbourhood of Carrickfergus.* In the year 1902 the county of Antrim yielded 32,529 tons of rock-salt, and 12,063 tons of salt from brine-springs. MINERALS OP MUNSTER. (No*. 1634 to 1644.) It is probable that the earliest workings for metalliferous minerals in the province of Munster were those in the copper deposits of the Knockmahon district, on the coast of Waterford. In this locality the " old men's workings " have yielded rude implements of stone and wood, pointing to mining operations at a remote period. The ores occur in lodes running through Lower Silurian (Ordovician) strata, associated with igneous rocks. No. 1634 is a sample of copper-pyrites from Knockmahon. The lodes yielding the copper also frequently carried silver-lead ores.f Ores of cobalt have occasionally been found in association with the copper-ores of Waterford, and the specimen, No. 1635, from Bonmahon Head, shows the erythrite, or cobalt-bloom, in company with an incrustation of malachite ; the characteristic pinkish tint of the former strikingly contrasting with the green colour of the latter. Another group of copper-ores is represented by Nos. 1641 and 1642, from the south-western part of County Cork. Although the minerals are rather widely distributed throughout this district, it is only in a few localities that they have been found in sufficient quantity to be profitably worked. The Bear haven or Allihies Mines, which at one time were extremely productive, are situated in a secluded part of the promontory between Kenmare and Bantry Bays. The ores occur in quartz-lodes coursing through killas, near the junction of what is often regarded as the Upper and the Lower Old Red Sandstone. { No. 1636 is a sample of copper-pyrites from Bearhaven, whilst No. 1637 is a specimen of erubescite, or purple copper-ore, from Ballycummisk Mine, near Skull. Lead-ores, associated to some extent with the ores of zinc and copper, occur in the Carboniferous Limestone of County Clare. The specimen of coarsely crystalline galena, curiously striped, No. 1038, is from a pocket in the limestone at Ballyhicky Mine. An interesting mineral found in the Carboniferous rocks of Kilbrickan or Monanoe, in County Clare, was described by Dr. Apjohn as far back as 1840, *"The Salt Industry of Carrickfergus." By A. Miscampbell. Trans. Fed. Inst., vol. vii. (1894), p. 546. t Mem. Geol. Surv. Explanation of Sheets 167, 168, 178, and 179. By G. V. Du Noyer, 1865. % Ibid. Explanation of Sheets 197 and 198 (1860). Notes on the mines by Warington Smyth, M.A., F.B.S., p. 3Q. AJso Explanation of Sheets 200, etc., 1861. 232 MINERALS OF IRELAND ANT) ISLE OF MAN. under the name of Kttbrickanite (No. 1639). This is a sulph-anti- monite of lead which has been recently shown by Mr. G. T. Prior's analysis to be identical with the species geocronite. This analysis revealed the presence of arsenic to the extent of 4-59 per cent.* From a quarry of Carboniferous Limestone at Rockforest in County Cork, was obtained some years ago, the beautiful mineral which Prof, Harkness named Cotterite, in compliment to Miss Cotter through whom it was procured. A specimen is here exhibited, as No. 1640. This mineral is a variety of quartz, remarkable for its peculiar silvery lustre, associated with a pearly sheen. The cotterite forms thin laminae, coating pyramidal quartz, and enclosing delicate films of limonite between the lamina?. It occurred in a quartz vein, covered by a thin layer of fine reddish clay, and Harkness suggested that the clay had yielded silica which was deposited on the quartz in a laminated form, the delicate lamination being responsible for the peculiar lustre. f The series of Irish minerals is brought to a conclusion by several fine specimens of Wavellite (Nos. 1641 to 1644), from Clonmel in County Tipperary. These are beautiful mammillary masses of fibrous structure, displaying on fracture a radiate formation recalling that of the well-known wavellite of Devonshire, but on a rather- bolder scale. Wavellite occurs likewise in the Lower Carboni- ferous rocks of Co. Cork. MINERALS OF THE ISLE OF MAN. (Nos. 1645 to 1652.) A few specimens placed at the end of the collection serve to represent, though imperfectly, the minerals of the Isle of Man. The mineral resources of the Island have been fully described by Mr. G. W. Lamplugh in his comprehensive official memoir,! a memoir in which he has given an historical account of local mining. and has added a list of all the minerals, comprising upwards of seventy species, known to occur in the island, whether in lodes or as rock-constituents. || By far the most important minerals, from an economic point of view, are the ores of lead and zinc. The sample of galena, No. 1645, represents the lead-ore of the famous Foxdale Mine. Here, the lode, or system of lodes, runs in a direction almost due east and west for a distance of between two and three miles, and has been worked down to a depth of nearly 2,000 feet. The vein passes from the Manx slates into granite, and it is notable that although it is equally * " The Identity of Kilbrickanite with Geocronite." Min. Mag., vol. xiii. (1902), p. 186. | " On Cotterite, a new variety of Quartz." By Prof Harkness. Min. Mag., vol. ii. (1878), p. 82. J Mem. GeoL Surv. " The Geology of the Isle of Man." (1903.) Op. cit., p. 480. |! Op. cit. p. 572. MINERALS OF TSLE OF MAN. 233 productive in both types of " country," the galena in the slate or killas, is found to be richer in silver than that in the granite. In the specimen, No. 1645, which came from the Townsend Mine at Foxdale, and was presented by Capt. W. Kitto, the galena is crystallised in cubo-octahedra. In the specimen of Polytdite, or argentiferous fahl-ore, No. 1646, the proportion of silver, accord- ing to Mr. David Forbes, amounted to 13-57 per cent.* This mineral was found in the easterly workings at Foxdale, where the lode passes into a granite country. Another interesting mineral from the Foxdale Mines is the Plumosite, or " feather-ore," of which No. 1647 is an excellent example. This rare mineral was described by Sir Warington Smyth, at the time of its discovery, about 1880.f It occurred in association with fine-grained galena and with vuggy or cellular quartz. The plumosite somewhat resembles cotton-wool, of dark colour, and consists of a felted mass of bright grey metallic hairs. It is a sulph-antimonite of lead, which may be regarded as a capillary variety of jamesonite. According to Capt. Kitto, the plumosite occurred only in the neighbourhood of galena that was rich in silver. In the year 1902 the Foxdale Mines yielded 4,192 tons of lead- ore, from which 62,000 ounces of silver were obtainable. A large specimen of galena, in aggregated cubo-octahedra, associated with blende and dolomite, from the Laxey Mines, will be found in the lower part of the pedestal case, on the opposite side of the Museum, near Section Q of the Horse-shoe Case. This huge specimen was pre- sented from the Great Exhibition of 1851. Rich silver-lead ore was formerly raised at the famous Laxey Mines, and at one time copper-ore was produced there, but the work- ings at present are directed to the extraction of the ores of zinc. Nos. 1648. 1649, are samples of the blende of Great Laxey. The ores occur in a lode of very variable width, coursing in a north-and-south direction through slaty flags, of the Manx slate series. The chief minerals are blende and galena, in a gangue consisting mainly of quartz and calcite. In the Wall-case No. 12, on the opposite side of the room, are some very fine specimens of blende, with crystallised quartz, from the Laxey Mines, presented by Capt. Rowe. In the year 1902, Great Laxey yielded 963 tons of blende ; whilst about the same amount was obtained from Snaefell Mine, situated three miles N.W. of the village of Laxey. Very curious globular masses of radiated blende were yielded at one time by the Townsend or Cornelly Mine a mine established on an east-and-west lode parallel to that of Foxdale. One of these spheroidal masses, presented in 1878 by Capt. Kitto, is exhibited in Wall-case 28. The specimen is broken across in order to display the radiate structure of the blende, and to expose the central mass of quartz and copper-pyrites. * " Researches in British Mineralogy." Phil. Mag., 4 ser., vol. xxxiv. (1867), p. 329. f Trans. R. Geol. Soc. t Corn., vol. x. (1887). p. 82. 7882, H 234 MIXRUALS OF THE ISLE OF MAN. Ill the specimen, No. 1G50, from Laxey, crystals of copper -pyrites are seated on the eroded surface of a large rhombic dodecahedron of zinc blende. A very handsome specimen, of similar character, will be found in Wall-case 12. In No. 1051, also from Laxey, the copper- pyrites is crystallised on well-defined rhombohedra of dolomite. The latter mineral is by no means uncommon in some of the Manx lodes, and remarkably fine crystals occasionally occur. Copper- ore is found in subordinate quantity in many of the mineral- veins, but the most notable occurrence was at the old Bradda Mines, where the copper-pyrites was associated, as at most of the other localities, with argentiferous galena. The lode, forming a conspicuous feature in the fine cliffs of dark slaty rocks at Bradda Head, was regarded by Sir Warington Smyth as '' the noblest surface exhibition of a mineral vein to be seen in Europe." In discussing the origin of the metalliferous deposits in the Isle of Man, Mr. Lamplugh is disposed to connect them with the volcanic activity of the Tertiary period, suggesting that the fissures through which the igneous material of the dykes was brought up may have served also as conduits for the vapours and solutions which deposited the mineral matter of the lodes. Hcematite has been worked in the neighbourhood of Manghold Head, in the north of the island, where the ore occurs in bold veins coursing through the slaty rocks of the cliffs. The source of the haematite may probably be referred, as Mr. Lamplugh suggests, to the New Red strata which are believed to have formerly overlapped the slates. The specimen, No. 1652, presented by Sir W. W. Smyth, in 1861, is a representative of the anthracite, which was found, at that time, in the Laxey Mines. This specimen was obtained from a depth of 110 fathoms. Unfortunately, the exact mode of its occurrence has not been recorded, and it remains doubtful whether it occurred as a constituent of the lode, or was derived from the adjacent slate. If really a vein-mineral, as some authorities have held, its origin may have been similar to that of certain graphitic substances that appear to have no relation with altered vegetable matter. The occurrence of graphite, in very limited quantity, has been recorded from the Snaefell lode and from Beary Mountain, in the heart of the Isle of Man. For a brief notice of the probable mode of formation of graphite, reference may be made to p. 160. INDEX. Actinium, 80. Actinolite, 101. Adipocere, mineral, 121. Aerated Baiytes, 170. Aetites, 194. Agate, 218. Alabaster, 182. Albite, 100. Alcohol (galena) 137. Allophane, Devon, 103. - Kent, 200. Alluvial Tin-ore, 18. Almandine, 100. Alquifoux, 137. Alstonite, 171. Alston Moor, minerals of, 161. Alum clay, 230. Aluminite, 201. Aluminous iron-ore, 230. Amber, 203. Amethyst, 92. Analcite (analcime) 217, 221, 228. Anatase, 100, 128, 191. Andradite, 101. Andrewsite, 53. Anglesite, Anglesea, 127. - Derbyshire, 139. Leadhills, 207. Anhydrite, 185. Anthracite, 234. Antimonite, 59. Antimony glance, 59. ores, 59. Antrim iron- ores, 229. Antrimolite, 229. Apatelite, 197. Apatite, Cornwall, 23. Cumberland, 153. Apochromatic lenses, 87. Aquamarine, 228. Aragonite, Cumberland, 149, 172. Devon, 98. Leadhills, 210. Argentite, 56. Arsenic, 32. Arsenical mundic, 31. pyrites, 31. Asbestos, 129. Asbolan, 125, 190. Asphalt, 178, 179. Associates of Cassiterite, 19, 21. Atacamite, 49. Aurichalite, Cumberland, 158, 167. - Leadhills, 209. Autunite, 83. Axinite, 30. Azurite, 46, 105, 190. Babel quartz, 91. Bagshot sands, 29. Balls, ironstone, 119. Barite, 168. Barium in natural waters, 187. Barytes, Cornwall, 95. - Cumberland, 151, 168. - Derbyshire, 135. - in London Clay, 188. in Lower Greensand, 188. - in Trias, 186. Barytocalcite, 171. Barytocelestite (barytocelestinu), 115. Bauxite 230. Bayldonite, 53. Beef (calcite), 202. Beekite, 97. ' Bell-metal ore, 20. Beryl, Donegal, 227. - Leinster, 225. - Mourne Mountains, 228. - Scotland, 220. Bindheimite, 59. Bismite, 79. Bismuth, native, 78. glance, 79. ochre, 79. ores, 78. Bismuthinite, 79. Bismuthite, 79- Bitumen, Elastic, 13-1. Black cawk, 160. copper-ore, 38, 44. Jack, 141. lead, 159. muckf 145. oxide of manganese, 77. - pyrites, 119. Blackband ironstone, 119. Blast ore, 144. Bleierde, 138. Bleinierite, 59. Blende, Cornwall, 58. Cumberland, 165. - Derbyshire, 140. - Isle of Man, 233. Wales, 124 hexagonal, 214. ruby, 124. Blister copper-ore, 36. Bloodstone, 144. Blue iron-earth, 71. John, 135. lead-ore, "55. stone, 127. vitriol, 46. Bogiron-ore, 193, 230. Bornite, 39. Botallackite, 49. Bournonite, 62. Boxes (pseudomorphs), 69. Brass ore 158. Brasses, 119. Brendon Hills, iron-ores, 105. Brewsterite, 211. Bristol diamonds, 113. minerals of, 112. Brochantite, 158. Bromlite, 171. Bronze, 8. Brookite, 128. Brown iron-ores, 193. lead-ore, 155. Brush ore, 116. Bull beef (fluor), 135. Buntkupfererz, 39. Butterfly twins (calcite), 132, 149. Buttons of galena, 163. Buxton diamonds, 136. Cairngorm, 220. Calamine, Cumberland, 166. Derbyshire, 141. Mendips, 109. pseudomorphs, 141. Calcite, Cornwall, 93. Cumberland, 149, 172. Derbyshire, 132. Devon, 98. - North Wales, 124. Strontian, 210. Calco-uranite, 82. Caldbeck Fells, minerals of, 152. Caledonite, 208. Campylite, 156. Cann (fluor), 86. Caoutchouc, mineral, 134. Capels, 11, 28. Capped quartz, 91. Carlsbad twins, 14, 99. Cassiterite, Cornwall, 8, 15. - Ross-shire, 220. - Wicklow, 223. Cawk, 136. Celadonite, 218. Celestite (celestine), 113, 186. Cellular quartz, 177. Cement copper, 44, 127, 224. Cerargyrite, 58. Cerussite, Cornwall, 56. - Cumberland, 165. Derbyshire, 138. Devon, 56. Leadhills, 207. Chabazite, 217,221. Chalcanthite, 46. Chalcedony, 96, 200. Chalcocite, 37. Chalcolite, 83. Chalcophyllite, 53. Chalcopyrite, 35. Chalcosiderite. 54. Chalcotrichite, 42. Chalybite, Cornwall, 69 Devon, 69. Durham, 167. Somersetshire, 105 Chamoisite, 192. Chenevixite, 53. Chessylite, 46, 105. Chiastolite, 159. Childrenite, 71. Chloanthite, 75. Chlor-apatite, 23. Chlorite, 101. Chloropal, 104. Chlorophaeite, 222. Chlorophane, 88. Chromite, 222. Chrysocolla, 46. Churchite, 83. day iron-stone, 119. Cleveland ore, 191. Cinoclase, 52. Clod (iron-marl), 116. Cluthalite, 217. Cobalt bloom, 76, 231. Cobalt ores, Cornwall 75. Ireland, 231. Cock's-comb barytes, 168. pyrites, 142. Cog-wheel ore, 63. Coke (calamine), 125. Comby lodes, 21. Condurrite, 64. Connaught, minerals of, 226. Connellite, 48. Copaline, 203. Copiapite, 197. Copper mica, 53. Copper, native 44, 213. Copper ore, black 44. , red 42. - vitreous 37. Copper-ores, Cheshire, 189. Cornwall, 33. Devon 33. - Ecton 142. - Ireland, 224, 231. - Leadhills, 209. - N. Wales, 126. Copper precipitate, 127, 224. - pyrites, 35. - shale, 189. - uranite, 82. Cornish diamonds, 91. Cornwall, minerals of 5. Cornwallite, 52. Cotterite, 232. Country (miner's toriu), 7. Covellite, 38. Crease, 116. Crested barytes, 168. Crocalite, 217. INDEX. -287 Oromfordite, 139. Cronstedtite, 73. Cross courses, 7, 54. Cross-course spar, 91. Crustification, 21. Cube ore, 72. Cumberland minerals, 143, 152, 161. Cupreous Calamine, 158. Cuprite, 42. Cupro-uranite, 82. Cyanite, 227. Cyanosite, 46. Dean Forest, minerals of, 116. Delessite, 218. Derbyshire, minerals of, 131, 137. Desmine, 217. Devilline, 47. Devon, minerals of, 5. Devonshire sand, 67. Diallage, 103. Dialogite, 77, 126. Diamonds, Bristol, 113. - Buxton, 136. - Cornish, 91. - Merthyr, 121. Dogs (pyrites), 117. Dog-tooth spar, 132. Dolomite, Cornwall, 94. - Cumberland, 149, 173. Isle of Man, 234. S.Wales, 118. Dolomitic conglomerate, 111. Dripstone, 133. Druses, 65. Dufreynite, 71. Eagle-stones, 194. Ecton minerals, 142. Edmgtonite, 218. Eisenkiesel, 92, 113. Elastic bitumen, 1 34. Elaterite, 134, Electric Calamine 159. Electrum, 130. Elvan, 7. Endellionite, 63. Enysite, 48. Epidote, 159. Epimorphs, 61. Erubescite, 39. Erythrite (erythrine), 76, 231. Exmoor iron-ores, 106. Eyam twins, calcite, 132. Eye agate, 219. Fahl-ore (Fahlerz), 64. False lead, 141. Felspar, 99 Felspar, kaolinisation of, 10. Ferberite, 153. Fire-stone, 199. Flats, 132, 162. Flint, 200. Float-ore, 162. Flos ferri, 172. Fluellite, 26. Fluor (fluorite or fluor-spar), Corn- wall, 26, 85. - Cumberland, 174. Derbyshire, 134. Devon, 86. N. Wales, 124. Fluor-apatite, 23. Fluorescence, 175. Fluoroid, 86. Forest of Dean, minerals of, 116. Fossils, old use of wood, 5. Fossil "oak" (barytes), 136. Francolite, 24. Fumaroles, 31. Galactite, 217. Galena, Cornwall, 55. Cumberland, 162. - Derbyshire, 137. Devon, 55. Isle of Man, 232. Leadhills, 206. Mendips, 108. - Strontian, 210. - Wales, 118, 122, 123. Gallium, in Cleveland ore, 192. Gangue, 84. Garnets, Cornwall, 100. Cumberland, 159. - Donegal, 227, Gas, natural, 204. Geodes, 65. Gilbertite, 27. Glauconite, 195. Goethite, 68. Gold, Cornwall, 18. Ireland, 222. Scotland, 205. Wales, 129. Goslarite, 139. Gozzan (gossan), 41. Graphite, Cornwall, 104, Cumberland, 159. Isle of Man, 23 i. Gravel ore, 123. Green lead-ore, 1 ">;"). linnets, 139. Greisen, 11. Grey antimony-ore, 59. copper-ore, 38, 64. iron -ore, 116. manganese-ore, 77. Groovers, 108. Grossularia, 81. Gruenlingite, 154. Gypsum, in Purbeck beds, 185. - in Trias, 182. Gyrolite, 222, 229. Hacked quartz, 91. Haematite, Cornwall, 67. 238 INDEX. Haematite, Cumberland, 144. N. Wales, 125. S. Wales, 117. Hair- pyrites, 120. Halite, Cheshire, 181. Ireland, 230. Halloysite, 103. Hard-spar (quartz), 90. Harmotome, 211. Hatchettine, 121. Haytorite, 97. Health- stones, 198. Heart-shaped calcite, 132, 149. Heavy spar, 168. Helium, 80. Hemimorphite, Cumberland, 158. Leadhills, 209. Henwoodite, 54. Hepatic alteration of pyrites, 197. Heulandite, 217. Hexagonal blende, 214. Highgate resin, 203. Highlands of Scotland, minerals of, 219. Hitchcockite, 156. Horn silver, 58. Hornstone, 97. Horse-flesh ore, 39. Huebnerite, 153. Huel, 13. Hydrargyllite, 99. Hydro-haematite, 147. Hydro-micas, 101. Idocrase, 227. Indigo copper, 39. Ireland, minerals of, 222. Iron bloom, 173. Iron glance, 147. Iron ores, Brendon Hills, 105. Bristol, 112. Cornwall, 65. Cumberland, 143. Devon, 65. - Forest of Dean, 116. Jurassic, 191. - Mendips, 1 10. Northamptonshire, 192. Yorkshire, 191. Weald, 193. Iron Pyrites, Cornwall, 60. Cumberland, 167. Derbyshire, 142. Wicklow, 224. -- in Neozoic Strata, 196. Iron-quartz, 92, 113. Ironstone, clay, 119. Iserine, 67. Isle of Man, minerals of, 232. Jamesonite, 59. Jasper, 129, 219. Jet, 202. Jews'-house tin, 7, 17. Joseite, 155. Jurassic iron-ores, 191,192. Kilbrickanite, 232. Killas, 7. Killinite, 225. Kilmacooite, 225. Kirwanite, 229. Kish, 160. Kupfernickel, 75. Kupferschiefer, 189. Lake iron-ores, 229. Lanarkite, 207. Lancashire, haematite of, 143. Langite, 47. Lapis Calaminaris, 109. Lateral secretion theory, 14. Laumontite, 217, 221. Lead-earth, 138. Lead-glance, 137. Lead-ores, Cornwall, 54. Cumberland, 161. - Derbyshire, 137. Devon, 54. - Isle of Man, 232. Leadhills, 206. - Mendips, 107. Shropshire, 177. Strontian, 210. Triassic, 120. - Wales, Mid., 122. Wales, N., 123. Wales, S., 118. Leader, 10 Leadhillite, Mendips, 108, Scotland 208. Leadhilis, minerals of, 205. Leicestershire, minerals of, 178 Leinster, minerals of, 222. Lepastrum, 188. Lepidocrocite, 148. Lepidolite, 27. Levyne, 229. Liassic iron-ores, 191. Libethenite, 51. Lime-uranite, 82. Limnite, 195. Limonite, 68, 117, 194. Linarite, Cumberland 157. - Leadhills, 208. Linnets, 139. Liroconite, 52. Lithia mica, 27. Lithomarge, 103, 230. Lodes, 6. Loughs, 147. Ludlamite, 71. Lunnite, 52. Luxullianite, 29. Lyellite, 47. Magnesite, 102. INDEX. 230 Magnetic pyrites, 168. Magnetite, Cornwall, 66 - Devon, 66. Ireland, 229. Yorkshire, 192. Malachite 46, 105, 157. Malleable copper, 44. Man, Isle of, minerals of, 232. Manganese nodules, 126. Manganese-ores, Cornwall, 76. - Devon, 76. - N. Wales, 125. Manganese-Spar, 77. Manganite, 77. Marcasite, 198. Marmatite, 58. Martite, 66. Matlockite, 139. Melaconite, 43. Melanterite, 197. Menaccanite, 67. Mendip Hills, minerals of, 107. Mendipite, 108. Merthyr diamonds, 121. Mesolite, 217, 222, 229. Metalliferous slates, Wales, 121. Mexico, Huel, 57. Miarolitic structure, 228. Mica, 27. Micaceous iroii-ore, 67. Midland Valley, Scotland, minerals of, 213. Mid- Wales, minerals of, 121. Milky quartz, 129. Milled te, 120. Mimetite, Cornwall, 56. Cumberland, 156. Mineral adipocere, 121. caoutchouc, 134. Minette, 192. Minium, native, 206. Mispickel, 31, 62. Mock-ore, 141. Molybdenite, 154, 179. Molybdic ochre, 154. Molybdite, 154. Monazite, 100. Moonstone, 183. Morvenite, 212. Moss agate, 219. Mother of lead, 163. Mottramite, 191. Mourne Mountains, minerals of, 228. Mundic, 60. Arsenical, 31. Munster, minerals of, 231. Murchisonite, loO. Nail-headed calcite, 172. copper-ore, 37. Native bismuth, 78. copper, 44, 213. ~ gold, 18, 129, 205, 222. Native silver, 57. sulphur, 226. Natrolite, 217, 229. Natural gas, 204. Needle iron-ore, 68. tinstone, 16. Neozoic strata, 180. Niccolite, 75. Nickel, 120. ores, Cornish, 75. pyrites, 120. Nigrine, 227. North Wales, minerals of, 123. Northampton iron-ore, 192. Ochre, 111. Olivenite, 51. Onyx, 219. Onyx barytes, 136. marble, 173. Oolitic iron-ores, 191. Opal, 97. Orthoclase, 99. Paragenesis, 19. Passyite, 199. Peach, 101. Peacock copper-ore, 36. Pearl spar, Cornwall, 94. , Cumberland, 149. Pebble iron-ore, 229. Pebbles, Scotch, 218. Pectolite, 218, 222. Pencil-ore, 144. Pentlandite, 75. Penwithite ; 78. Pharmacosiderite, 72. Phillipsite, 39. Phosgenite, 139. Pigotite, 104. Finite, 100. Pins, ironstone, 119. Pipe veins, 132. Pisolitic iron-ore, Antrim, 229. - North Wales, 126. Pitchblende, 79. Plaster stone, 183. Plumbago, 159. Plumbo-aragonite, 209. Plumbo-calcite, 209. Plumosite, 233. Plush, copper-ore, 42. Pneumatolysis, 11. Poder, 44, Polianite, 77. Polonium, 80. Polytelite, 233. Potato-stones, 111. Potters' ore, 137. stone, 183. Precipitate, copper, Anglesca, 127, Wicklow, 224. Prehnite, 101, 216. Przibramite, 214, 240 INDEX. Pseudomalachite, 52. Pseudomorphs, 13, 55, 69, 142, 146, 163. Pseudophite, 102. Psilomelane, 77. Puddle-ore, 145. Purple copper-ore, 39. Pyrargyrite, 57. Pyrites (pyrite), Cornwall, CO. - Forest-of-Dean, 117. S. Wales, 119. in Neozoic strata, 196. Pyrites, arsenical, 31. hair, 120. magnetic, 168. nickel, 120. rhombic, 198. tin, 20. Pyritohedron, 61. Pyritoids, 62. Pyroelectricity, 159. Pyroemerald, 88. Pyrolusite, 77. Pyromorphite, Cornwall, 56. Cumberland, 155. Leadhills, 207. Pyrophosphorescence, 88. Pyrrhotite (pyrrhotine), 167. Quartz, Cornwall, 21, 90. - Cumberland, 148, 176. - Snowdon, 129. in Neozoic strata, 199. Quartz, milky, 129. Radio-active minerals, 80. Radio-tellurium, 80. Radium, 80. Rake veins, 131, 161. Rashleigh collection, 62. Ratholite, 218. Red copper-ore, 42. iron-ore, 144 Reddle, 111. Redruthite, 37. Re-entrant angles, 15. Resin, Highgate, 203. Restormel Royal Mine, 65. Restormelite, 103. Retinasphalt, 104. Retinite, 104. Rhodochrosite, 77. Rhodonite, 78, 126. Ribband veinstones, 21. Right-running veins, 161. Rock-crystal, 91. Rock-salt, 181, 230. Roscoelite, 191. Rose spar, 77. Rosedale iron-ore, 192. Rosin blende, 141. tin, 16. Round ore (galena), 123. Ruby blende, 124. Ruby copper-ore, 42. Ruddle, 111, 144. Rugg stones, 199. Rutile, 100, 128, 226. Saline alteration of pyrites, 197. Salt, Cheshire, 181. Ireland, 230. Sammetblende, 68. Sanidine, 99. Saponite, 103. Satin-spar, 173, 183. Saussurite, 103. Scarbroite, 200. Sceptre quartz, 225. Schaumkalk, 173. Scheelite 31, 153. Schiefer spar, 93, 210. Schillerisation, 103. Schorl, 28. Schorl-rock, 29. Schroetterite, 103. Scorodite, 73. Scotch pebbles, 218. Scotland, minerals of, 205. Seals on crystals, 162 Secretion, lateral 14. Selenite, 183 Serpentine, 102 Shining ore, 67. Shropshire, minerals of 177 Siderite, 69. Sidot's blende, 214. Silver, native, 57. Silver ores, Cornwall, 56. Slate spar, 93, 210. Slick ensides, 138. Slippers (pseudpmorphs), 70. Smaltite (smaltine) 76. Smith ore, 116. Smithsonite 158 Smoky quartz, 91, 148, 220. Smoky topaz, 220. Soap stone, 103. Solfatara, 31 Somersetshire, minerals of, 105. Soot, arsenical, 32 Spangolite ; 48. Sparable tin, 16. Sparry iron-ore, 106. Spathic iron-ore, 106. Spatum Islandicum, 124. Specular iron-ore, 67, 147. Sphaerosiderite, 120. Sphalerite, 58, 141. Stalactites, 133, 202. Stalactitic barytes, 136. Stalagmites, 133, 202. Stannite (stannine), 20, 23. Steatite, 103. Stephanite, 57. Stibnite, 59. Stilbite, 217, 221. Stilpnosiderite, 195, JNDEX. 241 Stokesite, 23. Stream tin, 17. Strontian, minerals of, 21U. Strontian spar, 211. Strontianite, 211. Strontium, 114, 211. Sugar-candy spar, 98, 202. Sugary spar, ,21. Sulphur, native, 18o, 226. Sulphur-ore, 224. Susannite, 208. Tallingite, 49. Tamarite, 53. Tarnowitzite, 209. Tavistockite, 99. Tennantite, 64. Tenorite, 44. Terra ponderosa, 1 ru. Tetradymite, 154. Tetrahedrite, 64. Thomsonite, 216. Thunderbolts, 198. Tile-ore, 42. Tin, black, 8. , native, 7. , needle, 16. , sparable, 16. , white, 8. Tin-ore, 15, 220, 223. Tin pyrites, 20. Tinstone, Cornwall 15, Ross-shire, 220. Wicklow, 223. Titanium, 191. Toad's-eye tin, 17. Toadstone, 131. Tooth-tin, 16. Topaz, Cornwall 25. _ Ireland, 228. Scotland, 220. Torberite(Torbermte), 83. Tourmaline, 28. Towanite, 35. Travertine, 133. Troilite, 141. . Trowlesworthite, 2b. Tungstic ochre, 153. Tungstite, 31, 153. Turf copper-mine, 127. Turgite, 147. Ulster, minerals of, 227. Unstable quartz, 92, Uraninite, 79. Uranite, 81., Uranium mica, 82. ochre, 81. ores, 79. Vadose region, 41. Vanadinite, 207. Variegated copper-ore, a. Varviscite, 179. Veins, mineral, 6, 84. Vesuvian, 227. Virgin copper, 44. Vitreous copper ore, 37, Vivianite, 70. Volborthite, 191. Vugs, 6, 85. Wad, 159. Wales, minerals ot, 117. Waringtonite, 47. Wavellite, Devon, 98. Ireland, 232. Waxen vein, 188. Wealden iron-ore, 193. Websterite, 201. Welsh Gold, 129, Western Isles, minerals ot, 221 Wheal, 13. Wheat stone, 138. White iron-ore, 106. White lead-ore, 138. Wicklow, copper, 224. gold, 222. Willemite, 158. Withamite, 219. Witherite, 170, 178 Wolfram, Cornwall, 30. Cumberland, 153. Wolframine, 31. Wolframite, 30- Wolfram ochre, 31. Wonder stone, 202. Wood arsenate, 51. - copper, 51. iron-ore, 68. tin, 16. Woodwardite, 47. Wulfenite, 154. Xanthosiderite, 195. Yellow copper-ore, 35. Zeolites, 215, 221. Zinc-ores, Cornwall, i>b. Cumberland, 165. Derbyshire, 140. Isle of Man, 233. Leadhills, 209. Mendips, 109. Zinnwaldite, 27. Zippeite, 81. Zwitter, 12. 7882. ' NW - DISS, EYE, &o. By F. J. BENNETT. 2s. NE - - HALESWORTH and HARLESTON. By W. WHITAKER and W. H. DALTON. Is. SE - - BURY ST. EDMUNDS and NEWMARKET. By F. J. BENNETT, J. H. BLAKE, and W. WHITAKER. 1. NE - - PARTS of CAMBRIDGESHIRE and SUFFOLK. By W. WHITAKER [and Others]. 2s. SE - - PART of NORTHAMPTONSHIRE. By W. T. AVELINE and RICHARD TRENCH. 8rf. NE - - PARTS of NORTHAMPTONSHIRE and WARWICKSHIRE. By W. T. 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