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I)i,,,tiiu' l,..,l.,Mi., Museum Bulletin No. 27 GEOLOGICAL SERIES, No. 35 FEBRUARY 28, 1918 CONTRIIUTIONS TO TIIK MINERALOGY OF HI ACK I AKE AREA, Ql EBEC by Eugene Poitevin and R. P. I). (;ralinm orr.wvA (iiv| KSMI \r I'klMIM, l!l Kl \i), !(,')(, IS < si III k'iewof Blark'ake and sui rounding country sho»inii topography. d -J ^^m 0U:f365(J0 CONTENTS. lairoduction. Gaulogy. Paw 1 i Kuc'kf of the lerpentlne Mt Orifin of the mineral* Minerals Nativ t-.nt Dt low! Sulphide* Molybdenite J j Chalcopyrite jj Py*" '.['."...'.'. IS * 12 ii H It U Oidde*. IS Anhydrou* oxide* jj Quart! ,^ Magnetite j^ Chromite «. Hydrou* oxide* »- Limonite .] Brucite ^ Carbonate* 2^ Anhydrous carbor.ate* „ Calcite Dolomite Siderite ^ 24 M Aragonite Hydrou* carbonate* 36 36 HydromagncMte ^ 30 30 Stichtite Silieatca ^ Anhydrou* *ilicate» ^ Feldfl)ar „ EnMatite and hyper»thene Diopelde ^ Augite ^ Amphibole ^ Garnet .j Chryaolite ,. Veiuvianite „ 63 Zircon. Epidote ^ Tourmaline 63 Hydrou* *ilicate* ^ Scolecite Mica. 64 CUnochlore Colerainite Serpentine Kaolin Titano-silicate Leucozene Phosphate TJ tpatite 64 66 73 II •1 $1 •1 Illustrations. pxct PUte I. BUcklake Frontispiece II. North end of Black Uke III. Granitic intrusion in peridotite, Hall chrome pit m IV. Ridges of serpentinized peridotite, BUck lake »^ V. Chromite pocket. Hall chrome pit ^^ VI. Montreal chrome pits VII. Main Montreal chrome pit ■ ■ _ VIII. A. Microphotograph of white diopside rock, natural light V5 B. Dump of the Standard Asbestos mine • ■ ■ IX. A and B. Microphotographs of ropes of garnet in feldspar in a gametiferous aplite, natural light .■■'..■ X. A. Microphotograph of radiated vesuvianite with diopside, ^ natural light •_ .". ' "j- ' ■ j B. Microphotograph of radiated vesuvianite with diopside. ^ polarized light ;"'" : '." V" '■" XI. A. Microphotograph showing drusy character of colerainite-beanng ^^^ rock, natural light ■,■■■,"■''•'■■.■■■ B. Microphotograph showing drusy character of colerainite-bear- ^^^ ing rock, polarized light XII. Microphotographs of colerainite crystals: ^^^ A. Natural light ^^ B. Polarized light ^^^ C. Polarized light , Figare 1. Black Lake area ^j 2. Diamond •$ 3. Aragonite. simple crystal ., 4. Aragonite. twin crystal ■■■■■ • , • , ;^_^ ' 5. Diopside. unusual habit, due to prominent development of the hemi- ^^ pyramid A(331) r i i. ■ 6. Diopside, unusual habit, due to prominent development of the hemi- ^^ pyramid A(331) ,, 7. Diopside showing new forms (front) 8. " « " (back) Yi 9. * average habit „ 10. " tabular habit ^ 11. " flat termination (front) 12. •' " " (back) Ys 13. " twin crystal • . . 14. Grossularite. rare six-faced octahedron u(8S3) ^^ 15. " exhibiting rare cube faces 16. Montreal chrome pit ■ ■ ■■ ; ; • •; .. ^_ 17. Vesuvianite. lilac crystal, average habit, when m(UO) is larger than ^^ 18. VMiwaniteVlilac crystal^ average habit, when a(lOO) is larger than ^^ m(llO) ;•••;■,■••. Si 19. Vesuvianite, lilac crystal, average habit, with striae ^^ 20. " emerald-green crystal 21. « average habit of pale yellow crystals 22! " average habit of emerald-green crystals I February 28, 1918. s Canada Geological Survey Museum Bulletin No. 27. GEOLOGICAL SERIES No. 35. Contributions to the Mineralogy of Black Lake Area, Quebec. By Eugene Poitevin and R. P. D. Graham. INTRODUCTION. The minerals described in the following pages were collected by the writers at diflferent times during the summers of 1913-14-15, from some of the asbestos and chromite mines and pits in the neighbourhood of Black lake (Plates I and II). The region is situated in the southeastern and northwestern portions, respectively, of Ireland and Coleraine townships, Megantic county, province of Quebec (Figure 1). The area •called "serpentine belt" mulurt I °^ ^^^ '"°®* important nber of deposits of chro- ' ' ' ' " """ '''''■' '■ " ' •'"- ■ '- ■ littently, worked for the Although mining operations have been carried on in the district for many years, and the geology of the area has been investigated in some detail, very little attention has been paid hitherto to the mineralogy of these deposits. J. A. Dresser, in 1910, was the first to call attention to the peculiar dykes of lilac vesuvianite at the Montreal chrome pit, and the specimens he collected were at that time examined and described by one of the writers. In this connexion it is interesting to note that several very poorly crystallized specimens of this material were subse- quently found, unlabelled, in McGill University mineral collections, having been apparently collected, or received, several years ago and set aside for examination; the locality given for these is the St. Francis mine, Coleraine district, Megantic county, which at the present time is known as the Black Lake quarry of the Dominion Mines and Quarries, previously known also as the Montreal chrome pit. Special attention was first called by Robert Harvie to the wealth •f mineralogical material which the district aflfords. He pointed out that a study of the minerals might throw some light on the genesis of Pbte Fipire lUuBtratlonB. pagk I. Blacklake Frontispiece II. North end of Black Jake " III. Granitic intrusion in peridotite, Hall chrome pit 85 IV. Ridges of aerpentinized peridotite, Black lake 87 V. Chromite pocket, Hall chrome pit °» VI. Montreal chrome pits VII. Main Montreal chrome pit VIII. A. Microphotograph of white diopaide rock, natural light B. Dump of the Standard Asbestos mine A and B. Microphotographs of ropes of garnet in feldspar in a gametiferous aplite, natural light A. Microphotograph of radiated vesuvUnite with diopside, natural light '.. '"•,." B. Microphotograph of radiated vesuvianite with diopside, polarized light ■''".'■ A. Microphotograph showing drusy character of coleraimte-beanng rock, natural light ■ • • • • B. Microphotograph showing drusy character of colerainite-bear- ing rock, polarized light Microphotographs of colerainite crystals: A. Natural light B. Polarized light. . . C. Polarized light... minis'".""::::::: ,. . . ^"••"'■- Aragonite, simple crystal ' ■'«*• ■■''^. ''"•>*t Im,. of table, Aragonite, twin crystal. Diopside, unusual habit, due lo piu.u".^..^ — pyramid A(331) ,' ' u i, • Diopside, unusual habit, due to prominent development of the hemi pyramid i(331) Diopside showing new forms (front) " " " (back) • average habit * tabular habit « flat termination (front) « « « (back) " twin crystal .^ Grossularite, rare six-faced octahedron u(8S3) " exhibiting rare cube faces IX X. XI XII 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. IS. 16. 17. 91 93 95 95 97 99 99 101 101 103 103 for hS2° 7' read 32 32 32 33 33 34 34 35 Montreal chrome pit • ■ ■ ■ • ■ • ' Vesuvianite, liUc crystal, average habit, when m(llO) is larger than a(lOO) ,■•.•■, , • • 18. VesuvUnite, lilac crystal, average habit, when a(lOO) is larger than m(llO) 19. Vesuvianite, lilac crystal, average habit, with striae 20. " emerald-green crystal 21. « average habit of pale yellow crystals ^ 22. « average habit of emerald-green crystals ** IS- 51 53 53 55 5S February 28, 1918. Canada Geological Survey Museum Bulletin No. 27. GEOLOGICAL SERIES No. 35. Contributions to the Mineralogy of Black Lake Area, Quebec. By Eugene Poitevin and R. P. D. Graham. INTRODUCTION. The minerals described in the following pages were collected by the writers at different times during the summers of 1913-14-15, from some of the asbestos and chromite mines and pits in the neighbourhood of Black lake (Plates I and II). The region is situated in the southeastern and northwestern portions, respectively, of Ireland and Coleraine townships, Megantlc county, province of Quebec (Figure 1). The area is one of the most productive sections of the so-called "serpentine belt" of the Eastern Townships, and includes many of the most important asbestos properties; in addition, there are a number of deposits of chro- mite which have been profitably, though intermittently, worked for the past thirty years. Although mining operations have been carried on in the district for many years, and the geology of the area has been investigated in some detail, very little attenUon has been paid hitherto to the mineralogy of these deposits. J. A. Dresser, in 1910, was the first to call attention to the peculiar dykes of lilac vesuvianite at the Montreal chrome pit and the specimens he collected were at that time examined and described by one of the writers. In this connexion it is interesting to note that everal very poorly crystallized specimens of this material were subse- quently found, unlabeled, in McGili University mineral collections, having been apparently collected, or received, several years ago and set aside for examination; th. locality given for these is the St. Francis mine, Coleraine district, Megantic county, which at the present time IS known as the Black Lake quarry of the Dominion Mires and Quarries, previously known also as the Montreal chrome pit. Special attention was first called by Robert Harvie to the wealth •f mineralogical material which the district affords. He pointed out that a study of the minerals might throw some light on the genesis of 2 MUSBL'M BULLBTIN NO. 27. the serpentine and chrysotile-asbestos, and it is largely as a result oJ his suggestion that the present work was undertaken. Mr. Harvie also very kindly assisted the writers on one or two occasions in the collection of material, and has from time to time supplied them with specimens which he had himself collected. When the International Geological Congress held its twelfth session in Canada in 1913, an excursion (A5)' was made to the asbestos and chromite deposits under the direction of T. C. Denis and J. A. Dresser, with R. Harvie as guide. This excursion proved of exceptional interest to mineralogists, who were able to collect specimens of many of the minerals now described in this bulletin. The writers wish to acknowledge the courteous treatment they have in all cases received from the management of the various asbestos and chromite pits visited, where every facility was freely accorded them, both for the examination of the deposits and also for the collection of material. They are indebted to John Stansfield of McGill university, who has made most of the microphotographs, and to G. G. Clarke of the Geological Survey, who made the remainder of the series. It is with great pleasure that the writers take this opportunity to record their indebtedness to R. A. A. Johnston, mineralogist and curator, for much helpful criticism and many useful suggestions while the work was in progress, as well as for his kindness in reading and correcting the final manuscript. Both the collection of the material and its investigation were made independently by the writers until the present summer, when, at the suggestion of Mr. Johnston, it was decided that the results of the work might most conveniently be combined and published as a joint bulletin Accordingly E. Poitevin spent one month at McGill university col laborating with R. P. D. Graham, with this end in view. The results of this collaboration are set forth in the following pages, which are believed to present a fairly complete account of the mineralogy of Black Lake area. The crystallographic work was done at Harvard university under the direction of Professor C. Palache, at Cornell university and in the mineralogical laboratory of the Geological Survey, by Poitevin; an i in Professor Beck's laboratory in Vienna and at McGill university, by Graham. Some of the chemical analyses have been made in the chemical laboratory of the Department of Mines by M. F. Connor, and the remainder at McGill university. Several of the minerals are exceptionally well crystallized and !■ many cases they further exhibit features, such as unusual habits, forms, or • Coagri* fteloglqiw international, compte-tendu de la XII leMion, Canada, 1913, page* 9U ami MIKERALOCY OF BLACK LAKE AREA. J colours, which render them additionally interesting. The area has y^lded one new species, which occurs in well defined, though minute, crysta s; this has been named colerainite and is described on page 66 In ac..uf.on to this several amorphous or very compact substances were noted, which present a somewhat unusual appearance, but these have been found on examination to be not sufficiently definite in chemical composition and other characters to admit of their being listed as new mineral species. For the sake of completeness a brief outline of the essential features o the geology of the area and a description of the principal rocks is given at he outset, for which, as well as for the map and much of the infor- mation relating to serpentine and chromite, the writers are indebted to ioTi; fT?K ^'Jl'T"? ^'^'' °" '^^ Serpentine and Associated Rocks of Southern Quebec- Following this, a section is devoted to a discussion of the mode of origin of the several minerals and finally, each mineral is described in detail. ^ GEOLCXJY. O,...^" "'^"''? T^y °/ ""^ ^^°'°^ °^ *^^ serpentine belt in southern Quebec was made by J. A. Dresser during the seasons of 1907 and 1909 and the conclusions he reached regarding the structure of the area, and the mode of origin of the asbestos and chromite. are set forth in a pre- aZ,n7 TfT?^* ''"^if'^'u '" ^^^^•' ^•"'^^ ^''«* t''"^ ^ considerable amount of field work has been carried out in the area by Robert Harvie but his investigations being still in progress, no final report hts yet appeared. The following summary of the general geology of Black Lake area is based on Dresser's report. The serpentine belt consists of a series of igneous rocks, for the most part of basic composition; areally these appear in a discontinuous zone striking from the state of Vermont across the province of Quebec with a northeasterly, or east-northeasterly trend. The exact Ige of Uieir intrusion is unknown, and it seems possible that it may not have been synchronous everywhere throughout the belt. Over a large oart of the province these igneous rocks are found intruding Pal^zoic sedi- ments of Upper Cambrian and lower Ordovician age; in adjacent areas to the routh. Silurian and early Devonian strata are not intruded* and northeast of Black Lake and Thetford. in the township of Broughton. the time of intrusion seems to have been slightly earlier than in the greater part of the belt, though even there it is at least post-L'Jet in age_and po.ssibly late Cambrian. In general it may be said therefore. ' G»oI. Surv., Can., Mem. 22, 1913. •Ibid. •GeoL Surv., Can., Sum. Kept. 1915, p. 2U. MUSEUM BUtLETIN NO. 27. that the igneous rocks of the belt are principally post-Ordovician in age, and were probably intruded in pre-Devonian time. While the rocks comprising this igneous complex are, for the most part basic, they actually range in composition from the most basic to the most acid types; the series may be said to include dunite, peridotite, pyroxenite, gabbro, porphyrite, hornblende granite, and aplite; although in the field there is as a rule no sharp line of demarcation between any two of these owing to the occurrence of intermediate types. Dresser believes that the whole complex presents a gradual transition from the composition of a dunite to that of a granite. These and other considerations have led to the view that the various rock types have all been produced by differ- entiation from a single magmatic intrusion. The rocks of the serpentine belt do not form a continuous unbroken band along their strike to the northeast, but appear as a series of isolated stock-like masses, which vary considerably, both in length and width. In the Black Lake-Thetford area, they outcrop in a northeasterly direc- tion for a distance of about 10 miles and roughly form two parallel bands about 2 miles apart, each of which is from 2 to 3 miles wide. Black lake is situated at about the centre of the northern band, on its northwestern margin. The two bands may be regarded as a batholith, or possibly a thick laccolith,* although actually they present the appearance of many isolated stocks, which may be connected with one another at depth. It is found that the different rock varieties are arranged in the order of decreasing density, or basicity, from the centre outwards. Thus in the ideal case and where there has been sufficient erosion, peridotite of the dunite type is exposed at the central part of such a stock, and as this is traced outward the rock is found to become progressively more and more acid, passing by gradual transitions through pyroxenite, gabbro, diabase, and porphyrite until at the margins of the mass it may be a normal hornblende granite. These different rock types are rarely sharply distinguished from one another, even the g-anite in some places having been observed as a differentiation product. More frequently, however, the granite, together with aplite, has been injected a little later than tf m"! intrusion, and it then appears in the form of dykes, sills, an intrusive sheets cuiiuig the other more basic types (Plate III). It should be stated that in Black Lake area erosion has truncated the stocks or the foliated laccolith, to such an extent that the more basic central or lower phases, especially peridotite, are now exposed almost to the exclusion of the marginal differentiates of more acid composition, ■ Harvie, in a private communication, liu informed the writers that in Garthby township, the serpentine has tiK form of a folded laccolithic sheet lying between quartsitcs beneath and slates above. See Sum. tbiVt; 1916. G*atogic*t Strrt^ Canada fi9ure 1 Diagram of pa, Meg^nti , acatmpanj, f„^mum a.jl>mm 6y I fhitn.n md If I 1 Figiire 1. Diagram or' part oC ColerMnc Township, negsntic County, Qumbec Legend VnttifHtrmnttttrnd Cr»nitm and^ptitr DUh^f brm€€im, pjro*»nltm,mte K' ;.l4;.';! ^fp^ntinm ant/ p^nitotite L-. Swpwitin* tnd p»ridatif * a^ V~m I Otromi • 111 I (protpaet Tirmtt, /iMa^ ^ L />« accnrnfity, *!,,«,„ «„/**» ^ f f*„trv„< ,.^ir/>0 Graham MIKMALr-JV or ULACK LA» ARCf J and granite appears only in the form of dykei. } i h. r. alihuuKh thei.- S~"'u'°^'" "' "•"*"y "^"'*^ »° collcctivtl i^ the "«rpentine belt, this IS owing to the economic importance of ti iscrpentini- and not to Its prominence; serpentine itself is the least ab. .dant rock prtM.nt and is. of course, of secondary origin, having beer, derived from the •Iteration of perklutite and pyroxenite. As a general rule in this area, foliation of the i;ncou» rocks due to regional compression, although obsenrable, is not * pronounced as Jt IS in the Broughton region farther to the northeast. Faults of small displacement are numerous in the serpentine, .,ut are less frequent in the other igneous rocks; many of these are due to small movements and have produced much slickensiding. Displarrmerts of m-veral feet are ■•^-ilefined i-\ -em of joints, poeicions fnany of the «elf ihe join system is *i.wn ir Figufi ' . on which >5«l aslx ftx^ am chromite iiwral, 4hich fuf afibestoa ,«r within A ^uare. Thew wht -e !iiey are i*h *n on also frequently found. The rocks havf which, in the peridotite, have detcrmi larger serpentine bands; in the serpi obscured by the shattered condition of it The general distribution of the roofct also are ir^rked the locations of tht ^. pitji. In each case these are indicated h\ i» inscribed within a circle, and for tfcr.. numerals are taken from Dresser's tk^- „ „.„ ^ ,^ „^ Map 23A. The more important occurw^wes of ea.. h of Hie two mineral's are given belo»r; in these lists, the princupal kxali ^ - hich spcdniens were collected are printed in italics. ne (4) Colerainc (5) Ireland (6) Colerai (7) (8) (9) JO) 11 (13: (14) (15) (16) (17) (18) (19) Com'tmmy. Oecunencet of Askatos. block A, Black Uke Chrome nJ Asbe^^ o» i:«H«snv range III, lot 26, King Bn» -o-i-nT. bJock A. BUck Lake (Jhromf .ad Aafean. • Standard A sbesio' .mpawf. American A sbt ampnx. range B, Iot8 30and31, mean A 1»^. block A, A merican A sbesi, Companv range B. lots 29 and 30, Jr^sim^Ashmst block A, American Asbestos Company. American Asbestos Company range B. lot. 27 and 28. west halfT (;m,m *. lot 28. east half, Soutkwark ptt. range A, lot 29, Dr. James Reed. range A, iol 28, Dr. James Reea. range B. lot 27, east half, BeU's AsUsht ^ntan-, mngt A, lot 27. Dr. Jamis Reed. ^^ '' C^f^i^ptHty. Occttrrences of Chrome Iron Ore. 11 Coleraine block A, Black Uke Chrome and Asbesto. Company. xr « . u n 21 22 • • (Black Lake chrome pU). nioon u r^u v..!* ^Biack Lake chrome ptt). Black Uke Chrome and Asbestos Company. range X, lot 19 northwest. block A. BhchLahe Chrome and Asbestos Company. Black Lake Chrome and AsbesUn Company. ColMmiat rnVMim ■UUITIM MO. IT, ■ block A. BlukUtt Ck^m ^ A,t^ company. ; • SlMiari A$tul»i Cmprmy ''"*" '*'^ ^• ^ ^-IWSl;*^ ^ ('Mw r^). D^^ ^^ •^^ *^>'*^,AmtHe*mthnmplt, RCX:KS OF THE SERPENTINE BELT oomplCT. ^ ' ^" ™"^"« *••* "°« ''^ic rock, of the of the nu« im^t^L^r ~"P°"^°" °' »yP'«»' -Pedmen. RtckAnalytn. HiO-110» , -_ H^+iio-....:::;:;:;::;::;::::;;;;ij:« •MiO prabablv low. i S*'i|««kLakeiUtioii. 2 Near Black Uke station. i ^t^y- «»afe n. lot 4a * ^^nhby, range II, lot 40. « he roughly estimated by mere inspection •f hand specimens, owing to the ckavage and somewhat bronzy lustre exhibited by this mineral; with increase in the amount of pyroxene the rock paaaea into a pyroxenite. In thin aectiona, it ia aeen that the iron ore cryatallized firat, followed by the olivine. The cryatala of olivine all have about the aame aize, and they are sometimes enckwed within the pyroxene, which forma rather large individuala, tuid waa the teat mineral to cryaUllize. The olivine ia aeklom entirely freah; alteration haa commenced aa uaual around the margtna of the cryaula, and along cracka traversing them, and aa the metamorphiam becomea more and more complete the rock paaaea over into serpentine. SEKPENTINB. The aerpentine, like the peridotite, ia uniformly dark olive-green when freah, weathering to a creamy colour. Since the alteration of the olivine of the peridotite commcncea on the aurface of the crystals, and all stages of the proceaa are to be met with, from the fresh original rock to the completely aerpentinized variety, it ia not aurpriaing that it is often a matter of difficulty to distinguish between perklotite and serpentine in exposures, or even in hand specimens. For this reason, the two, as well aa all partially altered peridotites, are generally referred to collectively at the mines aa "serpentine," and, using the term in thia sense, it may be said that many of the larger hills in the mining district, such as those near Black lake, are composed of serpentine (Plate IV). Serpentine proper, however, does not form large bodies; it occupies only small areas or zones within the peridotite (or related rock) where the meta- morphiam has been practically complete, and in this way it forms the country rock of all the asbestos and chromite mines. The rock has a massive compact texture, but contains occasional crystals of unaltered or slightly altered pyroxene; on freshly broken surfaces these are easily visible, owing to their cleavage and lustre, while on weathered surfaces they stand out in relief, as may be well seen near the summit of the hill adjacent to Black Lake village. When thin sections of the rock are examined, it is usually found that the whole of the olivine has been completely altered to serpentine, although MUSEUll BULLETIN NO. 27. ttLeU lT;alllel%r'"! T'^'^r^ ^ f-q-ntly traced; minute veinlete of para lei fibres of chrysotile may traverse these, markine no doubt, the positions of cracks in the crystals, along which therrS'n.z! at.on commenced Otherwise, the serpentine fibres have 3reX lillT 7T ^^^' ?''''^"' •" ''^" ^'""""t- '« ««^'dom completely altered, and frequently is only very little changed. Grains of iron Z TwhShT;"''' throughout the rock in much ?he same mint as th" in which they occur in the original peridotite. PYROXENITE. nvro!!n? '\''^^- ~"^'"' ""^'^ Py^""^"^ t''^" °«vine. it is named pyroxenite, and it is with a rock intermediate in composition be4^ pyroxenite and peridotite that the chromite ore-bodiefare "SS The pyroxenite is a dark green rock, and it is often very coar^^^- talhzed. as for example near the Danville asbestos mines. whereTe across, and occasionally as large as 5 inches by 8 inches. The pyroxene which IS by far the most abundant mineral, is largely diallage. ahhoueh of"rr 7ht'^ »>-« the optical character of'e/statite.'rd othet ZmT \u \ «^^s"bo'•dlnate amounts of olivine and of plagioclase feldspar, the rock passing with increase of the plagioclase into gabbro GABBRO. and J,^^"'f ^-P-^'"f tyP«s which are composed essentially of pyroxene IL tie ^.T7 Py/^^-^'te and diabase; it may be seen exposed a ong the roadside near the southeast shore of Black lake, and in many other places near the foot of the serpentine hills. The rock consists o^ ^y plagioclase and green diallage; but in place of the latter it may con fcun colourless hornblende, which is apparently secondary, and the rock may then more properly be called a gabbro-diorite. DIABASE. is JvL'^i^^'"^-^^" !^^ '^'"' '"'"''■^' composition as the gabbro. but no^SvW^ r •" 't"' ^"^ fine-grained, sometimes so much so tha no individual minerals can be distinguished by the unaided eye iZ 27^:::iX:T '^ "^"^"^'/^'^'-^^^^^^ ^y ^^^ occurren^lhr^ghoul the rock of yellowish-green streaks and spots, very conspicuous on weath- ered surfaces, of epidote. which has been derived from the alteration of Shows the diabase to be always rather highly altered, the original primary } MINERALOGY OF BLACK LAKE AREA. 9 constituents of the rock, plagioclase and pyroxene, having in very large measure been replaced by secondary products, including chlorite, epidote, quartz, calcite, leucoxene, and occasionally tufted aggregates of actinolite needles. Pyrite and magnetite are common accessory minerals. It is believed that there was no essential difference in the original chemical composition of the gabbro and diabase, but that the same magma has given rise to one or other of these rocks, according to the conditions of cooling. Diabase is well exposed along the Quebec Central railway between Black Lake and Thetford Mines, and also near the Roman Catholic church at Black Lake. In places, the rock, through loss of pyroxene, becomes more acid in composition and passes into porphyrite near the outer edges of the masses. PORPHYRITE. Marginal phases of the diabase frequently exhibit a porphyritic structure, in which phenocrysts of plagioclase are distributed through a groundmass which consists chiefly of fine granular chlorite and epidote. Although unimportant as regards the area it occupies, the porphyrite is noteworthy as marking the acid extreme of differentiation in many places. GRANITE. The granite is light-coloured, usually grey, but occasionally it has a pinkish tint. As compared with the basic rocks of the serpentine belt, it occurs only in small amount, but it is important owing to the favourable influence it seems to have had in the formation of the asbestos. Hills of granite are found in the northeastern part of Coleraine, and in other places the rock appears, probably as a direct differentiate, forming isolated masses which grade into diabase or porphyrite. More frequently, however, the granite occurs as dykes intersecting the more basic rocks, and such dykes may be seen in most of the asbestos pits. The rock is composed usually of quartz, feldspar (both orthoclase and plagioclase), and hornblende; in general, biotite is absent, although in certain localities it appears as an important essential constituent, more especially in the central parts of the larger bosses of granite, and there also the structure is often porphyritic. A little iron oxide is usually present. APLITE. Ferromagnesian minerals are absent from some of the dykes. In such cases the dykes are composed of quartz and feldspar only, and often they are so fine-grained that the constituent minerals cannot be distinguished in hand specimens. Such aplite dykes, while comparatively 10 MUSBVM BULLETIN NO. 27. rare, are of interest as representing the acid extreme reached in the differentiation of the magma, from which all the various rock types described above are believed to have separated in turn. ORIGIN OF THE MINERALS. The mode of origin of the serpentine (including chrysotile), chromite, brucite, hydromagnesite, etc., is well established or obvious and need not be discussed here. Many of the other minerals, however, occur in a somewhat unusual manner, which calls for an explanation. These are for the most part alumino-silicatesrich in lime, such asdiopside, vesuvianite, and grossularite. They are commonly found filling dyke-like fissures within the peridotite, or its altered equivalent, serpentine; these dykes sometimes consist entirely of compact granular aggregates of diopside, vesuvianite, or garnet crystals. The minerals just enumerated include some of the species most commonly formed in the contact metamorphism of impure limestones. In the present case, however, both the attitude of »hese deposits and the absence of limestone beds, preclude the possibility of their having originated in this way. The minerals do not occur as a contact phase, but as dykes or veins well within the basic igneous masses; and, more- over, the intruded sediments around the margins of the igneous masses do not include any limestone beds, but consist of Cambrian slates, sandstones, and quartzites. It becomes necessary, therefore, to seek for some other source for the lime and, at first sight, the igneous rocks with which the minerals are associated do not appear to be the source. The following figures taken from analyses by M. F. Connor, and quoted in Dresser's report, give the percentage of lime in the principal rocks which make up the mass of the serpentine belt: Lime Content of Rocks. CaO percentage Rock Locality 0-68 0-20 15-20 6-80 Peridotite Serpentine Pyroxenite Diabase Near Black Lake station tt a m Lot 40, range 11, Garthby, Wolfe county « « « u Thus the peridotite, which constitutes by far the major portion of the igneous masses as exposed in this area to-day, contains less than one per cent CaO. While the writers cannot claim to have made an exhaustive study in the field of the mode of occurrence of these minerals, they have had MINERALOGY OF BLACK LAKE AREA. tl 3 I ■5; an opportunity of examining them at many of the pits; as a result of these observations, they are of the opinion that the minerals were deposited in their present positions as a direct result of the last phases of the intru- sion, and that the lime they contain was probably extracted by magmatic waters from the already consolidated portions of the igneous mass. The processes involved are outlined below. It may be assumed that the large bodies of molten magma, which gave rise to the rocks of the serpentine belt, contained certain amounts of aqueous vapour and other volatile constituents which remained in the fluid state until after the main mass of the magma had crystallized. In the present case, the magma, during crystallization, underwent pro- gressive differentiation, until the portion last remaining in the molten condition had approximately the composition of a granite; this then invaded the already cooling, solid mass, giving rise to dykes and other intrusive forms. All the aqueous vapour and other volatile constituents of the original magma (the so-called magmatic "eritract") must have been concentrated in this last acidic differentiate and expelled when it consolidated. Although this was the last phase of the intrusion, and represents a period of relatively low temperature, these residual magmas were sufficiently fluid from the presence of hydious and other volatile constituents, to permit their circulation through the enclosing rocks. It is not believed that this fluid, as it originally separated from the magma, was sufficiently rich in lime to afford such minerals as diopside, vesuvianite, etc.; its chemical nature, however, suggests that it would have a very considerable solvent action on the walls of the fissures through which it passed, and it is believed that it has been responsible for the serpentinization of the rock in the neighbourhood of these fissures. The peridotite, however, always contains some monoclinic lime-bearing pyroxene, and the amount of this mineral is considerable in the rook associated with the chromite deposits, which is about intermediate in composition between a peridotite and pyroxenite. It is significant, there- fore, that the dykes bearing the above-mentioned silicates are more frequently met with, so far as is at present known, in the chromite pits than in the asbestos quarries. As there is an almost complete ai nee of calcite, in veins or otherwisp, traversing these rocks, the writers art of the opinion that the lime (and also alumina) present in the original rock and not required for the formation of serpentine, has been carried away in solution as silicate. Then, as these residual magmatic fluids rose ia the fissures, there arrived a time when, either owing to their cooling or to the fact that they were under diminished pressure, they became unstable and commenced to crystallize out, forming "dykes" or veins of such highly calcareous minerals as vesuvianite, grossularite, aad u MUSBUM BULLKTIN NO. 27 diofwide, the particular mineral formed depending, no doubt, on such factors as the composition of the fluids and on the temperature and preBsure. It will be noted that these are all high temperature minerals, that do not readily crystallize except in the presence of a mineralizer such as would be afforded by the volatile constituents of the residual magma. Although granite and aplite dykes are quite common, traversing the peridotite and serpentine in all the asbestos and chromite pits, n» reference is made in Dresser's report to their displaying pegmatitic structure. True pegmatite dykes do, however, occur, although as a rule they are much altered, some of the feldspar being almost entirely converted into kaolin. Molybdenite, zircon, and tourmaline have been found in small quantities in such dykes at one or two localities, as noted below. Some of the coarse diopside "dykes" also have a structure comparable with that of pegmatite. According to the view here outlined, the "dykes" of lime-alumina silicates are closely related to the granite and aplite dykes, the fluids bearing these minerals in solution, or in aqueo-igneous fusion, having passed along the same series of fissures in the already solid portions of the magma, and crystallized out as soon as the necessary conditions of temperature and pressure were reached. Some aplite dykes, examined in thin section, were found to be highly garnetiferous, though others were more or less free from this mineral. Many were found to be traversed by cracks and veinlets cemented by fine granular to compact grossular garnet (Plate IX). This last feature might be taken as supporting the view that the granitic residue of the magma first assumed the solid state, and was later injected by the residual magmatic waters which had, in the meantime, become enriched in such constituents as lime as a result of their solvent acfon on the walls of the fissures. The dykes compost ■< entirely of granular or massive garnet, such as those occurring at the Southwark pit and elsewhere, may then be regarded as the limiting phase of the above process, where, the granitic differentiate of the magma having all consolidated, the still fluid mag- matic waters have continued to flow along fissures and ultimately gave rise to dykes of garnet. At other localities, where difffrent conditions obtained, vesuvianite or diopside appear instead of grossularite. MINERALS. Altogether, some thirty-four mineral species have been observed in the various asbestos and chromite pits in the area. These are described in the following pages, the ^quence adopted being that of Dana's System of Mineralogy. IUj«BKALOGV OF BLACK LAKE AtEA. u Native Element. 1 -3 DIAMOND. Microscopic crystals of diamond were obtained from chromite of the Montreal pit by R. A. A. Johnston, mineralogist of the Geological Survey. The following is his description of the diamonds and the method of extraction.' "No. 1. This specimen consisted of a massive, shiny black, some- what granular chromite, more or less intimately mixed with some greyish serpentinous material. "A fragment was broken from this specimen and crushed to a powder passing a sieve of sixty meshes to the linear inch; this powder was, when treated in a separatory tube with Thoulet solution, of a specific gravity of about 3-0; the heavier separate which settled at the bottom of the tube weighed after washing and drying approximately 11 grammes; this was mixed with SO grammes of chemically pure dry carbonate of soda and the mixture fused in a large platinum crucible at a cherry red heat for nours; after cooling the melt was digested in cii Ued water to complete disintegration, the supernatant liquid filtered off, and the residue treated with hydrochloric acid to remove oxides of iron, magnesium, etc. About half of the chromite was removed in these operations. This course of procedure was repeated several times. It soon became evident that this method was of little effect upon the coarser particles of chromite that were being left after each set of operations. Fusion with bisulphate of pot- assium was then resorted to, and the residue from this treatment, which showed a number of minute diamonds along with some undecomposed chrom.te, was freed from the latter by a final fusion with sodium carbonate. "The residue of diamonds obtained in the manner indicated above was found to weigh nearly 7 milligrammes or 0-06 per cent of the heavy separate operated upon, which constituted nearly the whole of the specimen. "These diamonds appear to the naked eye as nothing more than dust particles; under the microscope, however, with a moderate power they 'IWd., pp. 83-84. Figure 2. Diamond ex- tracted from chromite col- lected at the Montreal chrome pit ; the crystals are microscopic in size, the one shown in the figure being enlarged nearly 1,000 dia- meters; it exhibits a parallel growth of octahedra, a feature which has been frequently noted in these minute crystals. 14 yUSBUM BULLEHK NO. 17. are seen to be perfectly transparent and beautifully crystallized; the niost common form is that of the simple octahedron; many of them though, are apparently combinations of the cube and octahedron. The hardness could not be determined with accuracy owing to the very small amount of material available for experiment, but in the course of their removal from a beaker with the aid of a camel's hair brush, it was noted that even such light pressure as was occasioned in this way was sufficient to cause abundant fine scratches upon the glass. When exposed to radmm emanations they can be seen to fluoresce distinctly, a test which IS regarded as conclusive evidence of the character of the mineral. "No. 2. From the same locality as the preceding specimen. A dull greenish grey serpentine. Treated in the same manner as No. 1, it gave negative results. "No. 3. From the same locality as No. 1. A bright pink vesuvianite. It likewise gave negative results. "No. 4. From near Black Lake station. A dull grey peridotite. It also gave negative results." When examined with a high power under the binocular microscope, the crystals are found to have, in most cases, an octahedral habit, and they frequently exhibit a parallel growth in the direction of one of the crystal axes, as shown in Figure 2, which represents a typical crystal enlarged nearly one thousand diameters. Sulphides. MOLYBDENITE. Dresser' mentions the occurrence of molybdenite in very small amount at the Caribou pit; he states that the mineral was found in vein- lets, enclosed in vesuvianite. The writers have collected a few specimens carrying molybdenite both from the Caribou pit and also from the American chrome pit. In each case the mineral is disseminated through a garnetiferous aplite in the form of minute flakes. These are seen especially near the contact between the aplite and the serpentine, and occasionally also encrusting the sei^entine as a film at the immediate contact. The molybdenite, however, is by no means abundant, and was observed in a few specimens only. A microphotograph of a thin section of the aplite from the Caribou pit is shown in Plate IX and the rock is described under garnet on page SO. One flake of molybdenite in this rock had a diameier of one^centimetre, but otherwise, both at this locality and also at the > IbU, p. 84. III>««AL0GY OF BLACK LAKE AREA. u American chrome pit. the crystals observed were in general very much CHALCOPYRITE. Chalcopyrite is found at many places along the serjxntine belt, as a pnmary segregation, and associated especially with the diabase In general, the mmera! occurs only in small amc mt. and this is parti cdarly true as far as the Black Lake area is concerned. On many of the Bpecmens collected mmute specks of a brass-yellow mineral, almost microscopic m size, have been observed ; these are soft and react for copper and are no doubt chalcopyrite. PVRITE. Like the chalcopyrite. this mineral has been observed only as a ^^Z !7*'^"^"^ .°^ ?^ d'^»'^- «"d gabbro. through which it is disseminated as occasional microscopic grains. Oxides. ANHYDROUS OXIDES. QUARTZ. rfvt.^'''""* ^?"'- '^' "^^"'■'^"^^ «s a constituent of the granite and aplite dykes, quartz is entirely absent from the area. A few crystals were obtained from a boulder found about 5 miles northwest of Black lake- these are associated with apatite, and the occurrence is fully described' under that mineral on page 81. ucscnueu The quartz crystals are perfectly colourless and transparent, and they vary m size up.to 5 mm. in width and 1§ cm. in length. The ^rSn^r' J ^'■^^"'P'' combinations of the prism with the rhombc fnldHi ' r^ '"'^r "u^''';^' ''"' '"""y °^ '"^^ '^••^^^ '"dividuals exhibit n addition faces of the right trigonal pyramid s(1121). A trapezohedron ;^s o°hr''M"' r ''"'^f °^ '^' "-y^*"'^' ^"^ '" «" '^^^^ ^here this face was observed the crystals were found to be right handed. rhnJ^l P"""".^^^^^ ^"-^ striated horizontally on all the crystals; the d^l and 1 r," ^"•^\^'"«°»h ^"d bright on the small crystals, but a'n"d f^^e ;rttrir ''' ''''''' °"^^- '''' ^"■«-^' 'y--^' --^ ^^^^^^ Some doubtful new forms were observed on one of the crystals smiir N-(iri2r'R;?T/rvr *•^^^^(^«^«>• '(^«")- pcmD. Vii-6i;. IN UU^;, R(2133). The edge rs is replaced by four very narrow oscillation faces, which, in their order from r to s. have S '(" IT) Of r ^K' I^' ''''-' (^ » '^' ''■'■^'■' (^ ^' ^)- ^"ns i* » i;. Of these, the last is a fairly well-defined face, but the others •* MUUUM BVU.ITIN NO. 27. are little more than striations or lines. The measured and calculated angles for these forms are as follows: Form i» fi G> Nieaiured CalcuUted Meuured CalcuUted ♦ 1 1 :Yi ♦ VI 27* 03' 24 09 20 31 17 56 26* 59' 24 00 20 38 17 59 67' 38' 69 48 72 15 74 59 67» 35' 69 42 72 14 74 26 As these indices are calculated from single measurements only, the forms are not to be regarded as firmly cstablii.hed. MACNETITK. Magnetite occurs as a primary constifient of the basic igneous rocks, and also in the form of small irregular na&.es and veinlets within the massive serpentine, or associated with the chrysotile; it is also found intergrown with the chromite. In one interesting occurrence, nodules of magnetite up to 1-S cm. in diameter are completely enclosed within chrysotile, in such a way that the specimens have the appearance of a knotted string. However, when the chrysotile is stripped from the magnetite, the surface of the latter is found to bear the impressions of the asbestos fibres, indicating that in this instance the magnetite may have been formed later than the chry- sotile. CHROMITE. Deposits of chromite of workable size have been found at many points in the neighbourhood of Black lake, most of the productive mines being situated along the great serpentine ridge, which attains a height of 900 feet above the track of the Quebec Central railway; the locations of the more important pits are shown in Figure 1, page 5. Occurrence. The chromite does not occur in well-defined crystal individuals, but forms fine granular aggregates or apparently compact masses, having a black or slightly brownish-black colour, pitchy sub-metallic lustre, and brown streak. The compart ore often has a platy structure, breaking along ill-defined planes of parting, which, in some cases, are coated with a thin film of a white flaky biaxial mineral, which is probably clinochlore. The surface of the ore along such partings may also be highly polished or slickensided, due to diflferentia' novement or faulting subsequent to its solidification. MINIIALOGV or SLACK k-AH AIBA. ir The principal deposits of chromite have been found in a rock inter- medwte in composition between peridotite and pyroxenite. which represent tht two most basic, and earliest consolidated, phases of the differentiation of the magma which has Kiven rise to the igneous complex known as the serpentine belt. In shape, the ore-bodies are roughly lenticular, and they vary in size from small ptKrkcts up to masses contain- ing thousands of tons. As a general rule there is no sharply defined wall bounding these lenses, but the ore passes by rather gradual trans- itions into the country rock, through which chromite is then dispersed as scattered nodules and grains the size of a pea or smaller. When examined in thm section under the microscope, the chromite in these rocks IS seen to occur in isolated grains, and it displays the relations of a primary mineral. A very interesting occurrence of chromite is that at the Martin Bennett property (lot 28, range I. Ireland township). Besides occurrmg m massive form the mineral is also found as disseminated nodules enclosed in the serpentine adjacent to the massive chromite ore-bodies These nodules are of all sizes, from mere grains up to masses several centi- metres in diameter: one of the largest collected had dimensions 3J x 2} x li cm. At first sight they appear to be made up entirely of massive chromite. but. when broken open, it is found that there is. in addition a fair amount of interstitial serpentina, in part altered to brucite At the Hall chrome pit (Plate V) a granular chromite was observed, which IS so friable that it can be readily crumbled in the hand Analyses show that all the rocks of the serpentine belt contain traces or small percentages of chromium; this is probably present mainly in the form of chromite, disseminated through their mass in an extremely fine state of division, though it is possible that a little chromium may also enter into the composition of some of the ferromagnesian minerals wnicn these rocks contain. Origin. . ^ <^°"f ^^^«;!o"s such as those just enumerated, regarding the manner and attitude in which the ore occurs, have led to the view that the chromite was an original constituent of the magma, from which it ^parated by difTerentiaUon. This hypothesis was first advanced by K D. Adams' in 1894. and investigators who have since examined the de.wsits in the field have been practically unanimous in confirming this n" ■ , .VJ^''^"'^ ^°' **•'" """^^ °f °"«*" '^ thus summarized by uresser: The microscopic evidence that chromite occurs in isolated grains as a primary mineral. . eneral occurrence, in traces at least, ' TraM. Provfnce of Quebec Mining AMociation. 18M. • Op. dt., p. 9a W MUUUM aiTLLETIN NO. i7. in all the rocks of the series, the shape of the deposits, their relation to the wall rock, and the fact that they occur principally in a particular phase of the intrusive complex, viz., in transition rock between peridotite and pyroxenite, all go to support the opinion that the deposits were segregated from the magma of the original rock before it was completely solidified." Further evidence supporting the view that the chromite is primary is afforded by the discovery, made by R. . . A. Johnston, of microscopic crystals of diamond enclosed within the mineral. The theory that the ore was an original constituent and an early differrntiate or segregation product of the magma receives additional support from the fact that the granitic dykes, which represent the last phase of difTerentiation of the same magma, and which may be seen accompanying the chromite in most of the pits, have certainly been injected at some time subsequent to the formation of the ore -iKKJies. The frequent occurrence of granitic dykes within, or close to, the ore-bodies has been noted by many obse-vers. F. Cirkel, although expressing the belief elsewhere in his report that the chromite wa> formed during the cooling of the magma, goes so far as to state that these intrusive dykes exert "quite a favourable influence upon the deposition of the mineral."' The field evidence, however, all points to the ore aa having been solid before the dykes were injected, and the present writers cannot subscribe to the opinion that the latter could have had any influence, favourable or otherwise, on its deposition. If the dykes are actually more numerous m the vicinity of the rich ore lenses than elsewhere within the peridoti:e ?nd other a.ssociated rocks, a poini which has not hitherto been clearly demonstrated, it might be explained on the assumption that, as compared with the normal igneous rocks, the ore would constitute a brittle mass much more suscept- ible to fracturing than the relatively plastic peridotite. Further, the contact between the ore and the country rock, although nowhere sharply defined, should form a zone of weakness peculiarly prone to the develop- ment of fractures to be later filled by intrusivcs. This might explain the fact which has been repeatedly noted, that the ore-bodies are at times completely cut off by dykes. Where such magmatic injections have passed along fissures within the ore, they have frequently ripped off and trapped fragments from the walls, and these are now seen ."r.bedded within the dykes. The general shattering of the rocks which preceded or accompanied this last phase of igneous activity, and whose effects are seen especially in the peridotite, extended into the ore-bodies; as a consequence, the ore in many places > MliKi Bnseh. Can.. 1909, p. 23. 'Chrome Iran ore depotiu In the Eattm TowrKhips, Qiwbec," Report No. 19 IIIWBAtOCY or SLACK LAKB A»A. ,9 ha. a brecciatcd character, and .ubangular blocks and fraKmenu are conncc ed by .trmRcrB. vein., or wider band, of dyke mlteHal Th^ SZ rdi""-:,"" '" "'"^ '"^'' ^■^■' •• "«' «-"'»' at aSbu either impact d.op«,de or ve.uvianite. which ha. resulted from the pne" matoly^c action .^,llowing or accompanying the granite in.ruir « diM:UMH;d m an earlier section (p. 11). ■■>"u»mn», aa It may be noted here that the olwervation. of the writers lead them to beheve that many of the dyke. as«,ciated with the chrom te aVwelT ^rhap«. a. some of those cutting the peridotite and other^^k, nt"' Black Lake area which have generally been referred to a. "Ini ^ or B^an.t.c." W.11 be found on closer inspection to be composed S^mpac iX H^'f : "m"*^' °' -«"V'«"ite; Cirkel.. for ins^S. in dS ' ''llr 1 " ^Tt''^ '^'°"'' P'» (P'«'" VI and VII) sa>^ Another feature o the granitic dyke, in the Montrea pit worthy of attention is the peculiar colour which some of them exhibh SmaH ^kes have a distinct pink colour, and samples of the dyke pan e anTlv :^htSSL fdd°™r-'"' '"r^"'^"- "-'ver.^-hrorl' witli alkali (of the feldspar) gives a distinct purple colour, it is fair to It IS quite certain that the dykes to which reference is here made are th«e composed of lilac vesuvianite. and described elsewhe^ (p 5,? .n the H "V*"'" '^ ^""^ ^'"^^P^'°"^' -'°- there w'uldi nothill' l^r ^*^!^'P»'°" t° warrant one in regarding them as anything b"? granite. Many vesuvianite "dykes." however, as well as all H. composed of diopside and grossularite are white or pl^en colour « c losdy resetnble aplite that, unless examined indivWual ly Xy ;i;"h; easily be mistaken for such in the field. ^ ^ The shattering and brecciation of the ore have h^^n =. • j by faulting and sHckensiding. and in «,me SLs emir^lSrh":^ been cut off along the planes of such movement. *" o.,.l J .t''^""'"^ '^^l """ '''™'"'''= '« '" the main primary Dresser* quahfies this statement by adding: Lrresser "Subsequent solution and redeposition may have taken olace tn t: 7f::T' '"V°J t:!""' ^^^'"^' ^^ y^'^^ be nrc^ai^nr ZZ t '•"^".^^'"-'■'^^ bodies of chromite. which occasionally offshti o7 r '"-'T.' '^''"""^^ ^° ^'■^^'"^'^'^ '^-"^ -om uUra . T offshoots of chromite-bearing portions of the intrusive rock." The view that there may have been locally a partial re-solution of th^ chromite would seem to be confirmed by the o'::cu'rrence of Sep eme^^d! f!!!" chrome vesuvianite (and also of a crystal of ouvarovite)Tt the »Ol>.dt.,p. 27. 'Op.dup.9a 20 MVMVII BVIXITIN NO. 11. MontrenI chrome pit. The vesuvianitc w found either dep<»itc-d directly upon the aimpact chromite along narrow (ifam» and partinRn. or else lining drunes within the mawive white diop«idc which cemcntu the brecciated ore. It wou' « thus •cem that the magmatic waters, or "extract," which in an earlier section have been credited with exerting a powerful solvent action on the pcridotite and other rocks they bathed, have also been capable of dissolving the chromite with which they came into contact. It is also possible that some of the chromite thus taken into solution was later redeposited as a secondary mineral, since small veinlets of chromite are found, not only wit! in the country rock, but also penetrating the "dykes" of diopside and visuvianite. Microscopic Character. Microscopic examination of thin sections of the ore by Dresser revealed the interesting fact that it is not homogeneous but is made up of two distinct varieties of chromite, viz., a reddish-brown translucent substance and a black opaque material. The relative amounts of these present in the ore are variable, and Dresser was able to establish the fact that the high-grade ores contain as much as 90 per cent of the translucent variety, while in poor ores the black variety is greatly in excess. With regard to the microscopic character of the ore, he says: "Specimens of medium grades of ore show the two portions in the thin section to be definitely distinct from each other, though often intricately intergrown. In a few cases they had the appearance of inter- locking octahedral crystals, but in general crystal outlines cannot be well distinguished in either. Tn reflected light the two kinds of material are absolutely indistinguishable ."' The microphotograph of a thin section reproduced in his report shows the translucent variety with fairly sharply defined crystal outline, while the black material fills irregular spaces and sends off arms into the other. Judging from the photograph it would seem that these arms follow planes of cleavage or partings, since they show an obvious tendency to parallelism, both among themselves and also to the crystal outlines. In this connexion Dresser remarks: "In some sections the relative positions of the translucent and opaque portions are such as to suggest that the opaque might be an altered form of the other, but in others both appear to be primary."' Chemical Composition. Dresser treated a quantity of the crushed ore on a Wetherell magnetic separator, in an attempt to isolate the two varieties, the translucent >Op. dt., p. 77. •Op. dt., p. 79. MIN*IAL(MiV or IILAJK LAKt. AMEA. 21 reddwh-brown material being Im magnetic (as wtll a* IJKht.-r ami iiu.rc fnabk) than the black opaque portion. The two iiortionn wert- then analyiird and yielded the following rcKults:' AnalyuM of Chromik. R«l el The measured and calculated angles for tl follows: he form F (3584) are as Measured Calculated f . 8 .60 • OS' R° M' p 00 ^0 %^ 24 MUSEUM BULLETIN NO. 27. Occurrences. Montreal Chrome Pit. The best crystals were found at the Montreal chrome pit, especially in vugs in the massive lilac vesuvianite rock, or coating the slickensided surfaces of certain fissures in the serpentine. Three diflFerent habits were noted: one of these shows the simple acute negative rhombohedron f(0221), like the common form of " Fontainebleau sandstone"; a second habit is also a simple negative rhombohedron, the so-called "cuboid" ^(0554), and crystals of this type might easily be mistaken for chabazite. In each case these usually occur as interpenetra- tion twins, with twin plane_c(0001). The thiid habit is prismatic, the formsexhibited being m(lOlO), the positive rhombohedra r(lOll) and M(4041) and the scalenohedron r(3S84) ; M is larger than r while r(3584), although appearing as very bright facets on all the crystals measured, is almost microscopic in size. The rhombohedral crystals are seldom more than 1 mm. in diameter; the prisms are similarly thin needles with a length up to 2 cm. The massive calcite occurring at this pit is occasionally mangani- ferous, forming transparent or translucent cleavable masses of lilac colour. Caribou Pit. Crystals of calcite are found w=thin the druses of a miarolitic granite of aplitic_ character at this pit; the calcite, in simple negative rhombohedra f(0221). rests upon crystals of white albite which forms the walls of the druses. American Chrome Pit. The grossular garnet described below (p. 48) as exh>»-' v the very rare cube faces, is associated with massive white calcite DOLOMITE. Although carbonates of lime and magnesia are abundantly associated uith serpentine in many regions where the latter rock is found, in the serpentine belt of Quebec they are seldom met with, and then only in small amount. Dolomite may occasionally be seen as very narrow veinlets following joint planes which traverse the massive serpentine. Poorly crystallized specimens were collected from the Black Lake Consolidated Company's chrome prospect on the east side of Kings mountain. T' -rystals are very flat rhombohedra, with a somewhat lenticular form and a rough drusy surface. SIDERITE. Only one occurrence of siderite was observed . Brown rhombohedra, with a diameter of about half a centimetre, are associated with the apatite crystals described on page 81. « ^ MINERALOGY OP BLACK LAKE AREA. 35 ARAGONITE. As with calcite, the best examples of aragonite were collected from the Montreal chrome pit, where it occurs in druses associated with vesuvianite in its various colours, colourless diopside, ye!lowish-green '/ f k k /pi 1 p \ / / " \ \ \ \ n '/ / / p/ \ If \ k / r I -'A J, Figiir« 3. Aragonite from Montreal chrome pit, simple crystal with prom- inent development of thp prism m (110). Figure '. Aragonite from Mon- treal chrume pit, crystal twinned onm(llO). garnet, and clinochlore. With the exception of calcite, it has been thf last mineral to be formed here. The crystals are colourless and trans- parent or occasionally milky, and, for the most part, they are simple u MUSEUM BULLETIN NO. 27 individuals having an extremely thin bladed habit, tabular parallel t< the brachy-pinacoid, a(OlO); Jess frequently they are twinned oi m(llO), and sometimes stout six-sided prisms are met with as th( result of the repetition of this mode of twinning. The bladed crystals occur either as isolated individuals or in radiate: or tufted groups, implanted upon the vesuvianite or other matrix- thej measure less than 1 mm. across the blades, with a length up to Lboul 3 cm., and they are seldom doubly terminated. The forms most fre- quently present are: a(OlO). m(llO). v(U31), i(021), k(Oll), x(012) p(lll) and n(122); of these, the domes (v.i.k.x) and the unit pyramid (p) are usually developed to about the same size, but n was only observed as a nirrow line face truncating the edge between k and p. In the prism zone, the brachy-pinacoid a is present almost to the exclusion of the prism m in the bladed crystals, but at times the mineral presents a difTerent habit, with the prism (m) as dominant form, as shown in Figure 3. It may also be noted that in several of the crystals examined the forms m and a do r.ot form a true prismatic zone, being in reality an extremely steep pyramid and brachy dome, respectively, inclined to the vertical axis at angles of from 3 to 8 degrees. The twin crystals show two or more individuals in juxtaposition without re-entrant angles; a common type is illustrated in Figure 4. They exhibit the same forms as the simple crystals, except that n (122) was not noted; the dome x(012) also is sually not so large as the other forms. Aragonite in acicular crystals was also obse;ved filling small cavities in crystalline masses of amber grossularite from the Hall chrome pit. HYDROUS CARBONATES. HVDROMAGNESITE. Hydromagnesite is most frequently associated with brucite of which It IS the common alteration product. It forms stellate group's of radiated acicular crystals, having a white colour and somewhat silky lustre. Under the microscope the crystals show parallel extinction, and in convergent light an optic axis is usually seen to emerge obliquely, the plane of the optic axes lying at right angles to th~ length of the blades The mineral also occurs as a white chalky incrustation. The best speci- mens collected came from the American asbestos pits, but good spen- mens were also obtained at the Consolidated Asbestos and Chrome property from a new pit operated by Mr. Chretien; at the latter locality the radiated groups of needles, associated with the chromite, have an azure-blue colour which was found, on microchemical analysis, to be due to nickel. UINKKALOCy OF BLACK LAKE AREA. 27 In most of the open pits, joint planes in the massive serpentine are aeen to be coated in places with a thin deposit of hydromagnesite, in the form of stellate groups of acicular crystals. STICHTITE. The precious serpentine collected at the old Megantic mine, and described on page 77, sometimes includes small patches, or is traversed by narrow veinlets, of a lilac coloured mineral which has been identified as stichtite. Robert Harvie collected the first specimens of stichtite that were identified by the authors. Occurrence in Tasmania. This rare mineral was first found, associated with serpentine, near the Adelaide mine at Dundas on the west coast of Tasmania, and up to the present time it has not been recorded from any ether locality. The literature u^aling with the mineral has been collected and reprinted in a report' of the Tasmanian Department of Mines, published in 1914. In view of its interest in connexion with the occurrence at the old Me- gantic mine, a brief review of the history of the original stichtite is given below. Petterd describes the mineral as occurring in irregular masses, veins, and blebs in a pale yellowish-green serpentine, within which, also, it more rarely forms ill-defined bands. At times the serpentine is speckled with patches of stichtite, whir ■ vary in size from mere spots up to a diameter of 10 or 12 mm. Thv. colour is lilac, weathering to br' wn, ?.nd the mineral frequently encloses nuclei of chromite. Hardness 1}; specific gravity 2 • 20, ; nd also of a purer fragment, 2-12. The structure is foliated to compa> • granular. Owing to the common foliated char- acter, the mineral has a . .loritic appearance, and was at first referred to kammererite, under which name it appeared in the "Catalogue of the minerals of Tasmania" in 1896. Later investigations having proved that the mineral was a definite new species it was named stichtite, after Mr. R. Sticht, the general man»«»: "Note on Uw optical dauacteia," by L. K. Wanl 1 ii,,'*:.!?^™'' Chemical compoaltion." by Uura Iletner (Centralblatt f. Min.. etc.. No. 1», 1912, v-Ji^r. Jj™™ "*' °^'^°^ chararttr.," by A. Himmelbaucr (Tacherm. Min. u. Petr. MltUj.. Bd. JlXXII, Heft 1 u. 2, WI3, p. 1J3). 28 MUSEUM BIJLLETIN NO. J7. green sniution, but leaving a limited amount of flocculent residue; and t on heatinn it turns a bronze colour and becomes perceptibly magne More recently, the mineral has been analysed by Dr. Laura Hezi She refers to the stichtite as forming a rock mass composed almost tirely of a scaly mica-like mineral, recalling lepidolite, but with po< cleavitRc and a rather oily lustre; she states that the mineral appears have Ix-en derived from the serpentine, while grai,.j of chromite in latter have been converted entirely into stichtite. Dr. Hezner's ai ysis is reproduced in column (2) below. The author considers the S and FeO, shown in the analysis, to be due to admixed serpentine ; chromite respectively, and after removing these, the figures agree v ciosely with the formula Cr,0,.7Mg0.2CO,.12H,0 or 2Cr (OH),,S (OH),.2MgCO,.4H|0. This is taken as the formula for stichtite, ; column (3) gives the calculated percentage composition of the mine Analyses of Stichtite. SiO, COi Crrf), Ferf)i FeO MgO H,O-120».\ HJO+UO'I 7-2 11-5 90 36-0 36-1 99-8 3-87 to -45 20-44 110 37 12 0-95 26-31 100-24 tl-9S 20-65 38-06 29-34 10000 1. Analysis by A. S. Wesley. X \ alysM by Dr. Laura HeZner. S. Calculated percentage composition. Ward examined the mineral optically. Under the microscope found that it has the form of fibres and tufts, sometime, curved, radia disposed about nuclei of chromite. The radiating aggregates are wrapf round with a mosaic of small scales and fibres. He states that the m eral is not perceptibly pleochroic, that the fibres have parallel extinctii and are optically positive (measured with respect to their elongatio and that the birefringence is strong. The physical and optical characters were later determined Himmelbauer. He describes the mineral as occurring in scales wit! good basal cleavage. Hardness 1}; specific gravity 2-161. Optica uniaxial, or occasionally feebly biaxial, negative. Refractive index flakes, determined by immersion in a mixture of benzol and nitro-bena 1-542; birefringence, 6>-e = 0-026; pleochroism weak, w > c. He f ther states that the radial arrangement of the flakes around the chrom grains, as seen under the microscope, indicates that the latter mine MINERALCM.V OF BLACK LAKE ARRA. 29 ue; and that y magnetic, ura Hezner. 1 almost en- with poorer I appears to )mite in the zner's anal- ers the SiOi pentine and i agree very (OH),.SMg ichtite, and the mineral. tl-9S 20-65 3806 29-34 100-00 :roscope he ed, radially ire wrapped at the min- extinction, .'iongation), ^rmined by ales with a Optically ^e index of itro-benzol, €. He fur- le chromite ter mineral provided the chromium, while the magnesir Aras derived from the ser- pentine. Occurrence at Meganlic Mine. In general appearance and mode of occurrence, the stichtitc at the old Megantic mine is remarkably similar to that from Tasmania. More- over, the mineral so closely resembles, in its colour, the lilac vesuvianite (xxurring at the Montreal chrome pit, that it was not at f^rst distin- guished from the latter. The materi.il has not been analysed, but an examination of the general ch.-mical behaviour, as well as of the physical and optical characters, proves it to be stichtite. In making the indenti- fication, tlie several characters examined have been checked by direct comparison with those exhibited by a specimen received by tht Museum of the Geological Survey from Mr. W. 'I. Twelvetrees, government geologist of Tasmania. The stichtite apparently occurs very sparinsly, .md only a few specimens were collected. In these the mineral appears as small patches, ard also in the form of narrow veinlets, within the precious serpentine! The colour, on freshly broken surfaces, is deep lilac, but it weathers to a much paler shade. When examined with a lens, or, in some specimens, even by the unaided eye, the mineral -"s seen to be minutely crystalline, light being reflected from numerous very small faces, which are per- fectly flat and have a vitreous to oily lustre. These facets no doubt represent the basal cleavage referred to in the description of stichtite. and no fragment has been isolated showing cleavage in more than one direction. The mineral is easily scratched by a pin, and the hardness IS probably below 2. The specific gravity, by immersion in methylene iodide, was determined as 2- 166 and 2-185 on two fragments; it is very possible that the true value is somewhat lower than 2-166, since it is difficult to obtain fragments of the mineral entirely free from serpentine. When fragments are crushed in oil and examined under the micro- scope, they are found to be made up of minute thin blades or fibres, some forming a network, and others arranged nearly parallel. The colour is very pale lilac, and there is no perceptible pleochroism. The fibres invariably have parallel e. .^inction, and the birefringence is fairly strong. Compensation takes place when the quartz wedge is inserted normal to the length of the fibres, and the Tasmanian stichtite was found to behave similarly. Thus, as stated by Ward, the fibres are optically positive, measured with respect to their elongation. If, there- fore, the mineral is uniaxial, and the fibres are elongated in the direction of the principal axis, stichtite is optically positive, and not negative as would appear from Himmelbauer's observations. Notwithstanding the basal cleavage, the writers have in no instance observed a fragment to give an interference figure, as might perhaps have been expected, •• MUtKUM BULLKTIN NO. n. although a very large number were examined. Determinations of t refractive mdex, by the immersion method, were not altogether satisfa tory, but mdicated a value between 1-545 and 1-554. The powdered material effervesces when treated with dilute hydr ch one acid and the stichtite appears to be easily and complete soluble, yielding a bright green solution; an insoluble residue, howevc always remains, which is white and no doubt consists of the pale colour* serpcnline with which the stichtite is intimately associated. The fi tered solution reacts for chromium and magnesium. Heated before tl blowpipe, the mineral loses its colour and turns brownish or greenisl white, but It does not fuse nor become magnetic. The feebly magnet character after heating referred to by Petterd is doubtless to be asCTibc to admixed chromite in the Tasmanian specimens. At the old Megan.'i mine also, the adjacent serpentine includes a few small scattered grair of chromite. and it is no doubt from sach grains as these that the chrc mium of the stichtite has been derived. On most of the specimens collected there is a little magnesite c dolomite, in very minute white crystals, associated with the stichtit< especially where the latter occurs as n.xrrow veinlets. In view of thi it may be pointed out that the subtraction of one molecule of MgCC from Hezners formula would bring it into almost exact correspondenc with that earlier assigned to the mineral bv Petterd; but the description do not refer tr the presence of magnesite on the Tasmanian stichUt. specimens. Silicates. ANHYDROUS SILICATES. FELDSPAR. The various feldspars have already been referred to in the section deahng vth the rocks of the serpentine belt. The cystals of albite, mentioned above as occurring with caldte at the Canbou pit. are small prismatic individuals 2 mm. in lenirth exhibiting twinning on b(OlO). They are not terminated and are of no special interest. ENSTATITE AND HYPERSTHENE. These minerals occur as essential constituents of peridotite abd pyroxenite. and have been referred to under the descriptions of these rocks. DIOPSIDE. While diopside occurs at several localities in the area only that from I he Montreal chrome pit has been studied in detail. 1 »ll^fKl^ALocY or black lake area. 31 White, compact diopsidc rock occurs here as dyke-like IxxJies cut- ting the serpentine, and also in the form of narrow stringers and veinletn m the massive chromite; its mode of origin has already been discussed in an earlier section. Upon the walls of fissures and drur-y cavities within this massive diopside rock, where free crystallization has been possible, the mineral appears as small, but well formed, colourless, trans- parent crystals. A thin section of the massive rock photographed in ordinary light is shown in Plate VIII A. The rock has a granitic texture, and examina- tion shows It to be composed entirely of diopside, with the exception of a very little calcite or dolomite. The diopside is colourless, and very fresh and clear; it forms fairly large interlocking idiomorphic individuals, arid also granular aggregates of smaller crystals, which fill the inter- stices between these. Small druses are seen here and there, and it is in some of these that the carbonates have been deposited. A second variety of diopside is found in which the mineral forms large tabular crystals and platy masses with a white, or often pale lilac colour (the latter due to the presence of manganese). This coarsely rystallized material appears to be closely related to the other, and it often occurs in the same way quite close to the serpentine, from which It is separated only by a narrow zone of the compact white diopside. It seems reasonable to suppose that, under certain conditions, the solutions from which the diopside crystallized were cooled so rapidly in makmg their way along the fissures in the serpentine, that they were continually supersaturated, and the diopside crystallized out as a shower of minute crystals; this might be expected in the narrow fissures especi- ally and it would give rise to a "dyke" of compact diopside rock. Resid- ual solutions, filling cavities and druses in such rock, would then cool more slowly, with the formation of the colourless transparent crystals. Whe.e the fissures in the serpentine were wider, however, diflerent conditions would obtain; in such cases, the solutions would become highly supersaturated only where they were chilled by the serpentine walls. Elsewhere any crystals which formed might continue to grow until they ultimately formed a network stretching across the fissure It IS believed that the large tabular crystals and platy masses havt originated in this way. Colourless Crystals. Th^ colourless crystals are remarkable for two features: in the first place the occurrence of diopside in absolutely colourless and transparent crystals ,s in itself somewhat of a raritj-; in addition to this, the majority 01 the crystals present a habit, due to the large relative size of the faces St MV auixiTiM NO. ir. - .? fu J ?^!?^ ?" = "^*"' '''"^ projection of one of the ifwaiured mrrtah. •■tn the edge (331 : 331) vertical to em- nhowing two of the new fornu, ». (534) phasize the prwmatic appearance. and r. (T!-4-10). higure 7. Diopside, colourless crystal from the Montreal chrome pit; illustrate* the prominent development of the acute hemi-pyramid, J (331); the crj-stal also ex- hibits the new forms Y and J. Figure 8. Back view of Figure 7. KSL MINIIALOGV or BLACK LAKE AISA. M of the form 4(3(31), which appears to be unique, so far ai the writers can judge from a perusal of the literature to which they have had access. The crystals under consideration have the form of square pruma, terminated, in some cases at both ends, by various dome-like and other forms, and they are obviously monoclinic, with a vertical plane of sym- I / w crystal hographic of Figure 9. Diopside, colour- less crystal from the Montreal chrome pit; idealized inter- mediate habit representing the average of a number of crys- tals, but with the length of the prism somewhat exaggerated. Figure 10. Diopside, colour- less crystal from the Montreal chrome pit ; tabular habit with acute termination, the prism and the hemi-pyramid A (331) being the only forms prom- inently displayed; this illua- trates the average type. *• MUMlll BUI.LBTIN NO. j:. nictrj- pawing through the priitii. .Jiagonally. Without close inspectior the crystals might easily be mistaken for diopside of normal prismatic habit, presenting the unit prism w(nO); when measured and correctlj oriented, however, it is seen that the apparent prism consists in rcalit) of the four faces of the acute hemi-pyramid A(331), the angle 331 A 331 being 9r35'. The true prism zone has the forms a(lOO), f(31()) i(130), b(OlO), and occasionally certain others, as cited in the list below r • ' /r\ X Figure 11. Diopside, Figure 12. Back view of colourless crystal from the Figure II. Montreal chrome pit; crystal with somewhat flat termina- tion, due to the equal de- velopment of the pyramidal forms r_(Il2)j(Ill), *(221), and A(331). but these are all very small as compared with A(331). the only one of any prommence being a(lOO), while b(OlO) appears only as a very narrow line-face truncating the edge (331 :331). Other forms almost invariably present are 2(021), u(lll). x(221). s(Tll), 1(112), and the basal pina- coid. Figure 5 illustrates the habit and the relative development of the forms commonly exhibited by these crystals; it has been drawn with the edge (331:331) vertical in order to emphasize the prismatic appearance. One of the measured crystals having this habit is shown in orthographic projection in Figure 6. -.J .--«• MINKRALUGV or M.ACK LAU AUA. 35 Thcfc crystals measure up to 3 mm. in length and about 1 mm. across the prism. They occur in fissures and druses in the white massive diopside, notably in the immediate neighbourhood of the con- tact between the latter and serpentine. The commonly associated minerals are vesuvianitc and andraditc, both of pale yellow colour, and generally some thin blades of aragonite; the andradite in particular was noted as invariably occur- ring with the diopside of this habit. Less frequently, col- ourless crystals were obser- ved, somewhat similar in habit to that just described, but with the faces in the prism zone developed to about the same extent as those of the acute hemi- pyramid; Figures 7 and 8 illustrate this type. Like the last, these crystals are associated with the white massive diopside; but, it was noted that the druses in which they occur are almost always adjacent to veinlets or grains of chromite and that, in addition to the diopside, they usually contain crystals of emerald-green vesuvianite; other minerals which may be present are pale green andradite, calcite, and occasionally cimochlore. The diopside crystals measure up to 4 mm. in length and 1 mm. across the prism, but as a general rule they are rather smaller than this. Figure 9 shows an intermediate habit, idealized to represent the average of a number of measured crjstals, but with the length of the prism somewhat exaggerated. ttt Figure 13. Diopside, colourless crystal from the Montreal chrome pit; contact twin, with a(lOO) as twin-plane, parallel to which the crystal is flattened. W MUSBVM BULLETIN NO. 27. Another habit is illustrated by Figures 11 and 12. In this type the crystals, elongated in the direction of the vertical axis, are tabular parallel to a(lOO), the usual dimensions being about 2 mm. by i mm. Their terminations are flatter than in the crystals described above, owing to the larger development of the forms t(112), s(lll), and x(221) as com- pared with A(331). The basal plane is small but usually present. These crystals are, so far as noted, less common than the stouter types, and they frequently have a yellowish tint; they appear to favour the narrow fissures rather than the irregular cavernous druses in the massive diop- side, and are also found implanted on the walls of fissures in the chromite where they are accompanied by later crystals of emerald-green vesuvia- nite. Tabular crystals with acute terminations are also found; the prisms and hemi-pyramid A(331) are the only forms prominently displayed, and the basal plane is commonly absent. Figure 10 illustrates this type. Though twin crystals are not very abundant, a few were observed on the specimens collected. These are contact twins of the usual type and they are flattened parallel to the twin plane a(lOO); one of these, which was measured, is shown in Figure 13. White to Pale Lilac Diopside. This material is not well crystallized. Usually it forms platy masses which may have a surface measuring several square centimetres, with a thickness varying from that of paper up to 2 cm.; the plates or blades are intergrown in the form of an irregular network, intersecting one another at all angles and in all planes. The cellular spaces of this network have been more or less filled by the later deposition of crystals of pale green andradite and dinochlore, less often vesuvianite, both lilac and yellowish, and minute white calcite prisms. Occasionally imperfect crystals are found on these specimens; these are in the form of blades, tabular parallel to a(lOO), which is heavily striated parallel with the vertical axis and bevelled by narrow faces of the forms f(310) and m(llO) ; b(OlO) is small or absent. These crystals are comparatively large, measuring 1 cm. or more across the blades and several centimetres in length, and they are only slightly translucent. No crystals of this type were found showing terminations. Bright Honey-yellow Crystals. Small transparent crystals of a honey-yellow colour are fairly common at the Montreal chrome pit. They have the usual prismatic diopside habit; inspection indicated that no new or unusual forms were present, and the crystals were not measured. -^i^ltmmm'mmm UINBKALOGT OF BLACK LAKB AMA. VI Crystallography. Only the colourless, or slightly yellowish, crystals from the Montreal J chrome pit are dealt with in this section ; the specimens collected at other I localities have the more normal diopside habit, are in general poorly I crystallized, and present no unusual forms. A large number of crystals were measured independently by both writers, and upon these there were observed thirty-nine forms;' of these, twenty-eight have been previously recorded, while the remaining eleven are new for diopside. These forms are given in the following list, which I also indicates the frequency with which they occur on the crystals. i r»j.' ^^*>'-«'«'" 'o™» «* "•twi In Goldichmldfi WInktIubeUen (1897) ud dcbty-riz by Zunbaniai I L— . "'?*• "• "'°- **• '***• P- ^»)i 'ourtten •ddiUo-»l fomu uc reconlcd by WUtloek u haviaa si ""<*"'«<» »P to 1910 (School of MiawQuartwIy.XXXU. No. 1. p. 7J). 38 MUSBUU BULLETIN NO. 27. Crystal Forms of Diopsidefrom Montreal Chromt Pit Letter Symbol Occurs on all Occurs on most Rare; times Remark crystals. crystals observed 001 X Rare on tabi 010 X crystals. Usuallv ver small. 100 X 510 310 210 110 130 140 X X X X 2 Always nam Very narrow Always narn 1 Perfect face crystal of Oil 1 1 habit. 021 301 X 702 1 1 3 401 501 TOl 102 1 See Figure 6 2 Very small, 111 X Figure 13. 111 X Rare on tabu 521 X crystals. 331 X 441 2 See Figure* 332 Tl2 X Several and 8. See Figure 11 312 X Severa' See Figures 7, 9. 121 Several l31 1 1 5S2 I itm Forma. 610 3 Several 130-4 902 1 1 701 423 3 see Figures I3-4-10 Several < ^ and 8. see Figure 6. 534 773 Several S 1 iee Figure 6. "1 8- 11 -4. 1 N, 1.9.1 1 0. 1013-3 1 New Forms. The crystals are very perfect and the faces, includin] the basal plane, are unusually bright and yield single-image reflections The averages of the measured angles agree exactly, or to within a fcv MINERALOGY .ACK LAKE AREA. Reniarka ire on tabular crystals, ually very imall. ways narrow. ry narrow. ways narrow, rfect face on Tystal of flat labit. I Figure 6. y small, see 'igure 13. re on tabular rystals. Figures 7 nd 8. Figure 11. Figures 7, 8, Figures id 8. Figure 6. Figure 6. including ! flections, bin a few , minutes, with the accepted values (for Po = • 5390, qo " • 5670 or a ; 6 : c = 1-0934 : 1 : 0-5894 ; ^9 = 74° 9') and it has not been thought necessary to tabulate those for commonly occurring forms; those for the new forms are as follows: Letter Symbol Calculated values Measured angles, mean Yt 610 h - 80'" 17' \P - 90 00 = 80° 25' - 89 55 Dt 13-0-4 /#. - 90 00 V - 64 35 = 90 00 - 64 38 J. J02 U - 90 00 \p - 70 23 • 90 00 - 70 20 I, 701 !

- - 2 59 \p - 78 55J -- 3 lOi - 79 05 Oi Tg-13-3 U - -31 48 \p - 70 55 --31 29 - 71 06 The following particulars are added as indicating the manner in which these new forms were present on the crystals : .(610) D, (13-0-4) Ii. Y. .(902) .(701) .(423) .(i5-4-10) ....(534) Observed three times, on two crystals, one of which was a twin in each case, the prism zone was heavily striated vertically, but the faces (610) were fairly well defined. This form was observed independently by both writers on two crystals, as small, but fairly bright faces. Occurs on one exceptionally fine crystal as a very brilliant face of appreciable size (see Figure 7). Observed on one of the crystals of flat habit. This form was observed independently on three crystals, one of which is shown in Figures- 7 and 8; the faces are small, but suffi- ciently bright to admit of accurate measurement. These forms were present on several crystals, and are shown in Figure 6. The faces are in each case very minute, and did not yield very bright signals, but as will be seen from the table above, the mean measured angles a^ee closely with the values calculated for forms having these indices. 40 MVSKIII BlnXBTIN NO. 21. onlvT^.IT^'"'"*' T ^°"^ ^'^ *» N' O.) were observed on one crys ^^ brfSfsSr" ""^ "^-' ""'°^ '^^ ^^^- -^^^^ '^' -n^ for J^^f'^T- ^''*'°"«'' ^^"* °"« hundred forms have been record fod.ops.de. the crystals of this mineral are usually of fa.^y^ " ^ A arge major.ty of the recorded forms are rare and have beln oJ^rJ on^y on one or two occasions, or. in the case of many of them^^^ oTt e'crtr?r:mThfM ^r.^"^'' '''' forms\ave^S;n°?ot on me crystals Irom the Montreal chrome pit, and the historv nf ft,. irr ^'°"= ^"^"^^P-ticulars are abstracted from Zamb^nS exl^a same crystal XO^^h" fa« FC30lf '"' '""""°- »» ^h ^*°'^ |-'^^^*^->ri'»r„;^caTrr^^^^^^ C^arva shown in Figure 7. crysta. as a face of fair size am * ^'"'^ tLu^^Z^mL^^: ?y ^,'"^"™: »«th on crystal, f„,„ shown in Fig,?;^ 7Vlb, 13. ^^**''' ***'"'' °' *'''=*' ^r, " ^'°^^ te^T'i"'*'"^''"''.?" "y»t>>» from Testa Ciarva '' (^•'2) On Testa Ciarva crystals. _ '"'~''"^'*'<^^<: Observed on several crystals. '""^ S-''°^c52:^%?Ttt°es"<^X"' ^^^^ ^'-P"'. A-tria.. occur on the^fcrv^^? tt,?i? ' very acute hemi-pyramid ,"r "J!;{,. 00' ^-.^t.f, 'Op. dt. ''■ ^* *** 72 01 MINEKAUXiY OP BLACK LAKE AUA. 41 L (131) (f of Zambonini). First by E)aiia from Testa Ciarva; later by LaValle from Borne de Brous. Montreal chrome pit: Observed once on twin crystal as a very small face. ' (121) Given in Goldschmidt's Winkeltabellen, but is not mentioned in Zambonini's work on diopside. Montreal chrome pit: Observed on several crystals, one of them the twin crysut having the form L(T31) as a small face. ^1 (552) Has been noted on green crystals of diopside from Rotenkopf, Zillertale. Montreal chrome pit: On one crystal as a line face truncatine the edge (331:221). Chemical Composition. The material selected for analysis had a specific gravity of 3-267. The melt, after fusion, was coloured bluish-green, indicating the presence of manganese. The result of the analysis is given in column 1 below. Analyses of Diopside. ' 1 Montreal chrome pit (colourless) 2 Alatale (colourlRi^) 3 Nordmark (limpid) (Flink's type 4 Calumet island (white) 5 Near Ottawa (white) SiOi 54-77 0-17 0-89 0-11 18-46 26-33 54-74 2-91 1702 26 03 54-59 0-11 2-49 0-14 17-42 25-70 54-90 16-76 27-67 0-80 54-50 AI,Oi FeiO, FeO 1-98 MnO MgO 1814 25-87 0-40 CaO VoUtile 100-73 100-70 100-45 100- 13 100-89 2. Doelter, Tscherm. Mitth., 1877, 289. 3. Flink, Groth's Zietschr., 11, 476. 4. T. Sterry Hunt, Geol. of Canada, 1863, p. 468. , 5. Ibid., p. 467; white, semi-transparent, sp. gr. - 3-26 — 3-27, from the vicinity of Ottawa. The diopside thus approaches very closely to the theoretical com- position, CaMg(SiOj)i; there is very little ferrous oxide present, replacing magnesia, and alumina appears to be entirely absent. It is possible that a slight error in the determination of the ferrous oxide is responsible for the small percentage of ferric oxide shown in the analysis. Diopside with this degree of freedom from iron (and alumina) is somewhat rare. The analyses of two other Canadian examples are given in columns 4 and 5 above. In addition, columns 2 and 3 show the composition of colourless diopside from Alatale (Piedmont) and from Nordmark (Sweden), the latter representing Flink's type V; these are included for 42 MUSEUM BULLETIN NO. 27. compamon. and also owing to the close correspondence in optical TZ ^""Tu^' •"«*-"«' from these localitie^. anSJcrS the Montreal chrome pit, as detailed below. ^ Optical Characters. nf ■•nW«« 1 'Ti.i^ v^w.uui; vertical, immersed in Thoulet solu measured. The indices thus obtained are as follows : Method M.D., using prism 130A llO . Mp. usine prism 310a310 . I.R. from face (100).. 1-6691 1-6983 Light vit ing aloni axis 1-6765 1-6761 1-6873 1-6811 uwing to the small size of the orism farp« ft,» :ii • • a - 1-669, fl . 1-676, r - 1-698 iiigie oetween the optic axes, as they emerM fmm th^.l t measured with the crvstal mn m«^»^ j ."^^^ "^^^ t"ese faces, wj witn tne crystal mounted and immersed in Thoulet solutic MINERALOGY OR BLACK LAKE AREA. 43 I optical char- crystals from ing in possess- n expected in U. tal axes is as ^tallographic )f symmetry, ;n the crystal im deviation By the same vas obtained, g vertically, e also deter- vas mounted ilet solution e face (100) Light vibrat- ing along c- axis 1-6873 1-6811 ime applies to below, nation was It from the hods, it is if decimals, (le other is 00). The faces, was •t solution as before, and was found to be 59° 48'. From this value the true internal ■ optic axial angle (2V), the apparent angle in air (2E), and the position of i the acute bisectrix (giving the extinction angle on (010)), were calculated J to be as follows: ; 2V - S9» IS', 2E - 111- 54', Bx. A £ - axis - 38° 21'. The axial angle for red light is greater than for yellow (p > v), but it was not measured. Judging from the appearance, in ordinary white light, of the rings surrounding the optic axes, there seems to be a dispersion of the bisectrices in the plane of symmetry (inclined dispersion), but the effect may be due, in part at least, to a distortion of the interference figure under the conditions of the experiment. The value of 2V, calculated directly from the refractive indices ; a, P, r, is 59° 29', giving also 2E = 112° 30'; these are not very different from the corresponding angles as derived from the actual measurement. From this angle 2V, together with a knowledge of the extinction angle on (010) (-38° 21') and the angle 010 A 110 (-43° 35'), the extinction angle on (110) is found, by the usual formula, to be 32° 19J'. A large number of measurements of this angle, made on cleavage fragments, fell within the limits 32^°- 33°. It was not possible to measure the ex- tinction angle on (010) directly, owing to the small size of this face on the crystals. The acute bisectrix is inclined at 51° 39' to the normal of (100), and at 22° 31' to the normal of (001). The value calculated for the refractive index for light vibrating in the crystal along the c-axis (using, as data, a, y, and the angle Bx^Ac-axis) is 1-686; this is in fair agreement with the observed values noted ab^-/e. As will appear from the above description, the main interest of the colourless crystals, from an optical standpoint, lies in the refractive indices, which are as low as, or lower than, any which have hitherto been recorded for this mineral. The optical characters of diopside naturally vary with the chemical composition, and this is especially true with regard to the relative amounts of FeO, Fe,0|, and AljOi which may be present. In general it has been found that tb? iiearer the mineral approaches to the theoretical composition, CaMg(SiO,)i, the lower are the indices. In this respect, the Montreal chrome pit crystals may be compared with the limpid crystals from Nordmark, Sweden (Flink's type V), and also with certain colourless crystals fi n Alatale, Piedmont. Analyses of these are reproduced above, and their principal optical characters are tabulated on page 44. No. 1 refers to the Montreal chrome pit crj'stak. 44 MVKUM BinXITIN NO. IT. JJr^mark "'' * '° "^"'"'' ^™'" '^'"*"'"" '"'* ^°"- ' *"d « *« <=nr.tal No. I } 3 4 i 6 1-669 J -6707, 1-6710 1-676 1-6776, 1-6751 1-67681 1-6758/ 1-6780 1-69359 1-698 1-6996. •7000 2V 2E 59" 29' 59 09 39 18 59 IS 58 43 58 52 Bx, A 112* 30* 111 47 111 55 38* 38~ 38 39 38 the v^Iu^Vr U.7d«„1°' '^"°* ^'^''""> ''«"'*• *'»'' ">« '"ceptfen of 2 whici 2. Dufct Bull. Soc. Min.. Pari., 1887. 10. 221. AUGITE. Augite and diallage are not found in the area except as roc'c for AMPHIBOLI!. The minerals of this group occur only sparingly in the area IS Ta've" ' '"r"^"'^ ^^"^^^' ^"^ ^'« hofnblende is f^ue t^2^s^l)T^T K 'i'"\''°" ""^ distinguished by Ad, as louows. (I) The hornblende changes t . a scalv maw havJno. oU Te7r °'^!°"''- '"'"■^ ^°"^ '^ -* alwa>. present ^ There rone of fine needles, generally in tufts, with parallel extinction and wl have a brown or yellow colour. This colou'T. howeve does 'not l^ to the needles themselves, but is due to the separation ^f hydratid o of iron on the decomposition of the hornblendYmdecu^e (ir^um S^^ nf ?K T ^^^"^ ^'^ colourless, and probably the sam those of the yellow zone, but longer and finer " Hornblende having a clove-brown colour, in which respect it ,n, what resembles edenite. is found in the gabbro-diorite wWch form S a^liJ: aS TLTd T' I'' Quebec'central Ranry'l'ine l^Z ^rrion th u T^^^^'^i about a mile from the former place. In t section the rock .s seen to be a quartz-diorite; the hornblende has a n brown colour, and each crystal individual is' surrou'dS by a ^'„e' •GeoL Surr.. Can., Aim. Rept. Igge, JMI. 1882. p. gA. MINMALOGV OT M.ACE LAKE AIRA. 4S o cry«tal« from Bx. Acquit 3«' 21' 38 49 38 m 39 061 38 031 of, I which givct rock-forming gabbro, and e area. The 18 frequently ed by F. D. by Adams, iving all the 2) There is a n, and which s not belong drated oxide (3) Running iedles which the same as ect it some- ich forms a ine between ■0. In thin i has a pale ' a zone of •econdary actinolitic material, in the form of very pale green to colour- lesB ahredt or fibres. Short fibres, often radially grouped, of pale green actinolite, are •Modated with the colerainite in the spectmena from the old Standard mine described on page 66. GARNET. From a crystallographic standpoint the garnets are amongst the most interesting minerals occurring in this area. Crystals exhibiting two quite exceptional features have been noted; these are amber-coloured grossularite, fairly rich in forms which present the very unusual cube I faces, and pale rose crystals, which occur as simple six-faced octahedra. Still another point of interest is the occurrence of grossularite in colour- ' less crystals. Garnets were found at most of the localities visited, and are of two varieties, grossularite (calcium-aluminum garnet), and andradite (calcium-iron garnet). Only the colourless grossularite occurring at the Southwark pit has been completely analysed; beyond this, the classification of the crystals as grossularite and andradite is here based on their behaviour with hydrochloric acid and before the blow- pipe. Crystals which are partially soluble in concentrated hydro- chloric acid and yield gelatinous silica on evaporation, and which also fuse to a globule that is strongly magnetic, have been classed as andradite; those which do not give these reactions, as grossularite. Subdivided in this way it has been found that the colourless, rose, and certain greenish- yellow crystals are referable to grossularite, while the andradite is always olive to apple-green in colour; the former crystals moreover are usually transparent and dodecahedral in habit, while the andradite is inclined to be opaque and invariably exhibits the trapezohedron as the dominant form. The crystals are all rather small, none having been observed with a diameter greater than 1 cm. A description of the principal occurrences follows: Occurrences. Unim Pit. Cavities in a fairly compact, rose-coloured, grossular- garnet rock are lined with well crystallized garnet of the same or paler colour, accompanied in many places by a little aragonite and brown diopside. Many of these crystals are simple dodecahedra, while on others the trapezohedron «(211) is also present as narrow truncating faces. The dodecahed-jr: faces are frequently striated parallel to the shorter diagonal, and, wi the ca.» of some of the crystals, each dodecahedron face is seen to b. .:. re?lny double, being made up of two very slightly inclined faces, *• MoSBVM RILLKTIN NO. i7, whcwc edge is the shorter diagonai. and which belong to a very four-faced cube. Other crystals on the same specimens are more complex; as b< the dodecahedron is the main form, and its edges are tuncated by n( but there are also present the four-faced cube, g(320), and six-l octahedron. The faces of the latter form are curved, rendering a d mmation of the indices impossible. Perhaps the most interesting crystals occurring on these specin however, are those which exhibit the rare six-faced octahedron. u(l I his form occurs practically uncombined on the crystals, being ao panied only by very minute faces of the dodecahedron and the I faced cube g(320). as illustrated in Figure 14. The faces of the faced octahedron are usually striated parallel to their intersections the dodecahedron; in other cases they are curved and the form of crystal then approaches a sphere, whose surface is generally drusy Garnet is apparently the only cubic mineral whose crystals have 1 observed to bear the form u(853), and. so far as the writers are aw even with garnet it has only been recorded once previously This m the case of garnets from Rothenkopf , Tyrol, described by Cathrcin > states that the crystals were combinations of (110), (211) and (3 with faces of the new form (853) lying in the zone (110:101) on t sides of the d-xlecahedron faces. In the case of the Union pit crystals, this rare six-faced octahed is found, as already stated, practically as a simple form; crystals v selected whose faces yielded good single images, and the mean measu angles were found to agree closely with the calculated values, as folio The rose-coloured garnets have diameters up to half a centime! but the more complex crystals and the simple six-faced octahedra ; usually smaller than this. Andradite. both apple green and pale yellowish, is also found in t Union pit, but the crystals call for no special description Soutkwark Pit. The grossular garnet in the Southwark pit is rema, able .n that it is colourless and transparent; it forms granular. somewJ with a httle reddish-brown vesuvianite in prismatic crystals, and mini ■ Mia. MitUi., 10, 55, 18(18. MI.VeilAUMiY OF BLACK LAKK A«KA. 47 a very »teep ex; 08 before, Pd by n(211), and six-fai-ed ering a deter- se specimens, dron, u(853). being accom- ;nd the four- 8 of the six- Bections with form of the Jrusy. lis have been ■8 are aware, '. This was Uhrein,* who , and (321), 01) on both octahedron rystals were in measured I, as follows : ulated 1_ centimetre, tahedra are ound in the t is remark- , somewhat rossularite, uid minute j »ix-.sidrd flake* of dinochlore. Within the cavitits. where the Rarnet has had an opportunity to crystallize freely, fin.- trystalh occur plentifully, •omc of which attain a diameter «.f half a centimetre. In habit they are always dodecahedral ; occasionally this fr)rni occurs alone, but as a general rule its edges are truncated by narrow faces ol the trapezohedron n(211). In addition to these forms, the four-faced culx- «(61()) and the trape- tohedron m(311) were ol)servcd on one of the crystals measured; but in each case these latter forms were present only as minute facets, which did not yield bright signals. An analysis of these crysf \ gave the results shown in the last column of the following table: A nalyses of GrossulariU. Theoretical composi- tion 1 Wakefield (white) 3 Hull (^cokiurlesa) 4 Orforcl (yellowish- white) 5 Southwark pit. Black lake Molerular ratio SiOi 40-00 22-70 37-30 38-80 22-66 1-75 35-00 068 0-30 39-85 2207 1-13 36-31 0-68 .18-60 22-71 1-60 34-83 0-49 0-47 MO 39-49 22-35 1-00 36-62 0-28 015 AltOi •6.S8...3 FeiOi -219... 1 FeO CaO -014 -007 •002 MgO . .? MnO K,0 Hrf) — Sp. gravity Refractive index 100-00 99-19 3-525 l-7438« 10004 99-80 3-52-3-53 99-89 3-60 1-734 1. Buljman, Am. Jour. So., 27, 1884, p. 306. 2. Wulnng, 3. Priv. com. M. D. Munn (cited by Dana, p 440). y Gra"l^m."^'^^'°' ^^"^ '*"' "' *'*■ ^'^''* ^'^ ^"^ \nc\uAt^ some MnO). The composition of colourless garnet from Hull and of white garnet from Wakefield and from Orford are given for comparison. The refractive index was determined by the minimum deviation method using sodium light and taking the dodecahedron faces for the prism. Hall Chrome Pit. Specimens of grossularite were collected from the Hall chrome pit by J. Obalski' many years ago, and are now in the mmeral collections of the Geological Survey. Many spec-.nens from this pit were collected by the writers. The crystal.s h.ive an amber colour ■ Geol. .Suiv., Can., Ann. RfK„ vol. X. 1897. i,. tjjA. « MUSIUM ■UUinN l»0. IT. and dodecahedral habit, with minor development of the trapezohei n(211). Small Jnues in some of the specimena contain thin bladf aragonite. The garnet occurs at the contact between aplite and serpentin peridotite. Plate III illustrates the mode of occurrence of one of t aplitic intrusions at the Hall pit; in other places they have a r regular dyke-like form. Figure 14. GrossuUrite, rose-coloured cryital from the Union pit, has the rT' "L'"?* '"' V*'J^7^ o<-t,,hedror- «(8S3). with minor deelopment of the dodecahedron and the four-faced cube jOCO). Old Standard Mine. Small reddish-brown crystals of garnet oo here, associated with tourmaline, in a pegmatite dyke. Ameru-xm Chrome PU. The crystals obtained from this pit are r in forms, and are of especial interest in that they exhibit faces of the cul a form very rarely found on crystals of garne^. In general the ha is dodecahedral. modified by the forins n(21 1) and r(332) which are ab< equally developed: the remaining forms, s(321), e(210), and g(3; ■apezohedron lin blades of ierpentinixed one of theae lave a mort- ; has the nt of the arnet occur pit are rich of the cube, 1 the habit h are about ind g(320) MINUALOCV or BLACK LAU AMA. ^ appear cwily a« narrow truncating farm; the cube face* also are quitt •imall FlKiirt- IS iihowR the average habit of these cryiUls. It should be mcntiont-d that althouRh many of the crysUls were examined under I hi Wmnular microgcopc, only five or six were completely mcwured, and It h iMitmMv that additional forms would be found if a special investi- Kation were made; this remark applies also to the other garnet occurrentn. deMiitjed here. a™!^ „ L ^'^'^''!^'~^^-P^^e ^'"i>er (tuccmte) ,,.\uurtd crystal from the -.Tn^-. ? chrome pit nch in forms, and especi iliy interesting in that it exnibits laces of the cu!*, .1 form rarely found on garnet crystals. These garnets are grossularite of pale amber (ouccinite) colour, and usually they are about 2 mm. in diatn-ter; they are associated with white massive calcite in a compact, granular, olive-green diopside ock. Montreal Ch^ "/ \ndraditp i- the only variety of garnet noted at this localit^ • ,^ ;,, ..^ ^j^h pale ^rcen clino- ch lorr of rath^ ,„.t, , ., ^,^^ ,^, ^^j^^ ^^ P*'« '•'-'•-^ a-y.u- , .. diopside, ifarnet. 50 MUSBL'M Bl'LLETIN KO. 27. dinochlore, and there is usually also some later caicite in minute, whi prismatic crystals. The garnets are olive-green in colour and almi opaque; some crystals measure as much as 1 cm., but the more perf ones are not more than 3 mm. in diameter. Andradite of pale greenish-yellow colour is also associated hi with the massive white diopside, at the immediate contact of the lit with the serpentine; the crystals are smaller than the above, averagi about 2 mm. in diameter, and they are also more brilliant and tra: parent. The diopside crystals associated with these garnets have t habit described elsewhere in which the acute hemi-pyramid /l(331) is abnormally developed as to simulate a square prism. In each case the andradite crystals are quite simple; they are trapezohedral in habit, the form n(211) often occurring uncombin< otherwise it is modified by small faces of the dodecahedron, and occasic ally also of the three-faced octahedron r(332). A single isolated crystal found at the Montreal chrome pit has deep emerald-green colour and might be classified as ouvarovite. Caribou Pit. Fissures in a fine-grained, aplitic granite are h« found filled with colourless or pale pinkish, very compact, granu grossularite; no definite crystals have been observed. A micropho graph of the aplite in ordinary light is shown in Plate IX. Orthocla in fairly large individuals, is the principal mineral present, quartz bei subordinat Plentifully scattered through the orthoclase are sm grains of colourless garnet; these may be isolated, or packed closi together in granular lookin< clumps but their most characteris arrangement is in the form of straight strings, along which the lit garnets are strung out like beads. Some of these strings may be trac completely across the thin section, traversing in their course seve feldspar individuals. It is very evident, therefore, that the garnet later than the feldspar, and apparently it replaces that mineral. T only other mineral present in the section is colourless dinochlore, in sm amount, and this appears to have been introduced at the same time the garnet. It was in this aplitic dyke that the molybdenite referr to on page 14 was found. Black Lake Chrome and A sbestos Company's Pit, No. [18] . The occi fence of garnet at this pit is similar to the last. It is a colourless to p; rose grossularite, seldom observed in well-defined crystals, and it occi in association with a granitic rock which ic itself very highly game ferous. A thin section of the rock was found to consist for the most ps of garnet in comparatively large colourless individuals. Quartz a feldspar, both orthoclase and plagioclase, are present, but only in mir amount. The rock as examined is not very fresh; there is a fair amou of caicite and also some chlorite, the latter in places being much stain lute, white, and almost lore perfect ciated here if the latter !, averaging and trans- is Jiave the A(331) is so hey are all ncombined ; id occasion- e pit has a :e. e are here t, granular nicrophoto- Orthoclase, uartz being are small ked closely aracteristic \i the little Y be traced rse several e garnet is leral. The re, in small me time as ite referred The occur- less to pale id it occurs ly garneti- ; most part )uartz and ly in minor air amount ich stained fimn,,6 Sectjon showing matter Mon. 5n.!?5P^'*"a: J?vllrt,n by tJ^itam> ana ^fiO.Gmhaid Ona fhot """""' Sectjon showing disti uuti'n of ¥etn maUer, Montreal Chi o nn Pit . [!^\l j^j ^'t MWifr oFhlac vesuvianite crystals Efr? :^ Oruses lined with jellon vesuvianita tr="'^3 diopsideand aragonite I ^ I ^ona afmasaive white diopaide r* 'W\ ^°"' ofaerpentjne traveraed yyX by thraads atatbastoa a 1 1 ll *'"^"*' afperidotite carrying nillB diaseminatad chromite ^ ^i>^!S^£i%/^i';^i,Sx, in MINERALOGY OF BLACK LAKB ABEA. $1 by hydrous ferric oxide Some serpentine is also present in the section, being, no doubt, a portion of the dyke wall. Crystal Forms. The forms observed on the garnet crystals from the various pits, as far as they were examined, are as follows: Form Locality ^••:j a(lOO) Dodecahedron d(llO) Four-faced cube ". '. ;*(6io) . , , e(210) Three-faced octahedron r(332) Trapewhedron !m(3n) Six-faced octahedron. ... . .'.'.'..'. u(853) ! * '. .8(321) American chrome On all crystals 5yjuthwarkpit American chrome pit American chrome pit American chrome pit Southwark pit On all crystals Union pit American chrome pit Colour pit Amber Colourless Amber Amber; Union pit, rote Amber Colourless Rose Amber CHRYSOLITE. Chrysolite, or olivine, occurs only as a constituent of the peridotite and pyroxenite, and is described in the section dealing with thesTrocks. VESUVIANITE. Very finely crystallized specimens of vesuvianite are found at several bcahties in the area. The crystals have a brilliant lustre, are f"r ie Tk oTh r"' '^^r''"*' ^'"^. ^'^P'^y " ^'^^ ^^"«^ °f ~'°"^' '"eluding b oL w '• ' "^ ^een various shades of yellow, clove, and reddish! brown, and m some cases they are colourless; w.'h the exception of the brown variety the crystals seldom exceed one millimetre in diameter. Occurrences. Montreal Chrome Pit. This locality (Plates VI and VII and Figure 6) has furnished some of the best material examined by the writers larabrdl'r^"' ^^"°" ^"' -'""^'^^ ^-^^^- all'occurrngTn •naJs'^'h.v:^" vesuvianite forms compact, fine-grained, crystalline masses, having a deep tint which renders the specimens very striking aftertr' ^V''-'^'=JV'f ^^" '°""^ '''^' '"^^ ~'°"^ fadesTomewhaf ^he rriTr'" ° ^'^ ^^ ''«'^*- E'^^^-tion of thin sections shows that the rock does not always possess the same structure. The vesuvianite h^ the usual high index of refraction and very low birefringLilf tJe no^ceab^Te * f''*^' ' '^"*' ^"* ^"'^^ ^'-^^'"^^ pleochroism is dCtion ^f 1 ^' ' ?P^^""^ ""'""^'"^^ f°' '•^''^ vibrating in the So ^"'™ ^^' ^"^ P^'" '"'**-• '"' ^^^' vibrating normal 53 MITUUM BULLBTIN NO. 27. In some sections the rock displays a fine, even-grained, grar texture, being composed entirely of fairly stout interlocking prism: vesuvianite. Small driises are seen here and there. The prisms quently interpenetrate one another completely, and when this feal is pronounced, owing to the intersection of several prisms at a sii point, it forms a transition from the granitic texture to that now tc described. In this second type, a radial grouping of the vesuvianite individua characteristic. The radially orientated prisms dovetail into one and at their common point of intersection and give rise to spheres, or, in sect to circular aggregates. The spaces between these radial groups ma] filled with vesuvianite showing the ordinary massive intergrowth may be left vacant as druses; many of them, however, contain ra< coarsely crystallized colourless diopside, as well as some smaller gr of colourless garnet, both of which are contemporaneous with, or sligl later than, the vesuvianite. Plate X is reproduced from microph graphs of this rock, and clearly illustrates the various features referreTamid s, the other forms present, and t, having a relatively small development, and the basal pL either absent or of trifling size. Figure 18, omitting the basal would represent an average type. The minerals most frequently associated with the vesuv described above are caldte and aragonitc, the latter in tufted £ of flat bladed crystals; less frequently there are also present dio both colourless and yellow, and a white, amorphous material, po porcellophite, a variety of serpentine. The emerald-green crystals are always associated with white, coi diopside. The latter material, as already stated on page 31, fom walls and outer portionsof certain dyke-like bodies which cut the scrp< at this locality, and it also occurs as a network of irregular veins trav the massive chromite, giving to the ore a brecdated appearance, vesuvianite occurs as brilliant green crystals resting on crystals of o less or pale diopside lining cavities in this compact rock; similar cr are also found along fissures in the chromite, directly attached 1 ore, but as a rule these are poorer and almost microscopic. The habit of the crystals is illustrated in Figure 20 and Figure 22. The [ are square in outline, owing to the invariable predominance of i as compared with m(llO); the base, though small, is always pr The main pyramid in this variety is the ditetragonal form s(311), ai steep pyramid t(331) is also well developed. Owing to the large re size of these pyramidal forms, the termination of the emerald- crystals is, on the whole, more acute than in the other varietie complete list of the forms observed on these crystals is set forth i table on page 58. MINBIAI.OtiV or BLACK LAKB AREA. $$ m 0(01 1) was e lined instead .analysis of the >th manganese variety might iling, the most ;ed appears to ns; the mother X, until there e the effect of y the mother , the colouring t formation of }f the latter is le dominating present, m, p. basal plane is e basal plane, le vesuvianite tufted groups :sent diopside, terial, possibly vhite, compact 31, forms the : the serpentine eins traversing earance. The stals of colour- imilar crystal? :tached to the ic. The usual t. The prisms mce of a(lOO) Iways present. i(311),andthe ; large relative emerald-green varieties. A ;t forth in the It may be noted here that emerald-green chromiferous vesuvianite also occurs on the Monetnaja estate, Ekaterinburg, Urals. Pale yellow crystals also occur with the diopside in a manner similar to the above, but they are of a different habit (see Figure 21). Thr basal plane was absent in eight crystals which were measured, and wai not observed on others which were examined with a lens. The prisma a and m have about the same development, sometimes one, sometimes Figure 19. Vesuvianite fromthe Montreal chrome p't; illustrates the way in which some oi the lilac crystals are striated. Figure 20. Vesuvianite from the Montreal chrome pit ; emerald-^reen crjrstaL the other, being the larger, and the edge between them is invariably truncated by narrow faces of the form f (210). The crystals are terminated by the unit pyramid p(lll) as dominant form, with s(311) somewhat smaller; faces belonging to other forms, as listed in the table below, are minute and not universally present. Although these and the emerald- green crystals are obviously later than the diopside with which they occur, M MVMVM ■VU.BnN NO. 17. they were not found aMociated, in the apecimens collected, in sue way as would render it possible to determine whether or not they strictly contemporanet>us and formed under the same conditions. 1 Figure 21. Veauvianite from the Montreal chrome pit; average habit of the pale yellowish crystals. Figure 22. Vetuvianite from the Montreal chrome pit; average habit of the emerald-green crystals. difference in crystal habit, however, is interesting, as possibly indlcatii the influence of the presence or absence of chromium in determining tl forms developed on the crystals. lUNBBALOCT OT BLACK LAKB ABBA. S7 Cakite, aragonite, clinochbre, and porceliophite are the minerals moit commonly ataodated with the emerald-green crygtalt; the yellow variety haa in addition andradite associated with it. SoHtkuMwk Pit. Clove-brown and reddish-brown crystals are associ- ated with the colourless groflsular garnet described on page 46; the largest crystals observed have a length of 1-5 cm., and measure 4 mm. across the prism. Several crystals were measured aiid on these the forms tabulated on page 58 were noted ; the habit is usually determined by the forms a(OlO) and s(311); p(lll) is sometimes fairly large and the base is absent. Caribou Chrome Pit. This locality yields reddish-brown crystals of habit similar to the last. American Chrome Pit. Vesuvianite occurs here in compact masses of pale yellow colour; where more coarsely crystallized, it forms a network of prisms, but well terminated crystals were not seen. Union Pit. Bottle-green, as well as reddish-brown, vesuvianite occurs at the Union pit, but in neither case was it found to be well crystallized ; the former is usually associated with clinochlore and brownish diopside, the latter with colourless, rose, and pale green grossularite. Hall Chrome Pit. At this pit there is found a massive vesuvianite rock, almost uncoloured, associated with which are crystals having an emerald-green colour. Table of Occurrences. For convenience of reference, the differently coloured varieties of vesuvianite occurring in the area at the principal localities visited are tabulated below: Rt Emerald- Lilac to colourlew Pale yellow Rcddiah- brown Bottle- green Montreal chrome X z X X X X X z X Southwark Caribou American Union Hall Crystallography. About sixty of the crysvals were measured, these being chiefly of the lilac, emerald-green, and paK' yellow coloured varieties, which, owing to the brilliance of their faces, {-resent almost perfect material for gonio- metric work. The total number oi forms observed in this series of crystals » MITSKUM BI'LLKTIN HO. 17 was sixteen ; these forim are given in the following table, which alw how they were distributed anmng the differently coloured crystafc. Crystal Formt of Vtstmanile. Utter Symbol Lilac to cnlourlnw Emerald- green Pale yellow Ret 001 X X 010 X X ■ no 120 130 X X X X X X X X X 3S0 .VII 221 X X X X X 111 i.n 1.12 ?4I X X X X X X X X X X X X X X 121 X Oil X 4M X 151 — X No new forms were note I. anil all those observed are comn occurring and well LstaL!i';i ,- minute facets on the pale yellow crystals from the Montreal cfarorr the mean measured and the calculated angles being as follows: Measured Calculated v(151) / <» - "'"' 11«18' As has already been noted the same form probably .; urs ,. : lilac crystals from this locality, together with y(411) a, . ' ', '\. . three all lying in the striated zone (100) : (311). The other form, r(461), is marked as doubtful in GoM^.c r.^ Tabellen. It was here observed on one of the emerald-green < and although quite small, the measured angles agree so nearly witn calculated values that the form may be con.sidered as well establishe Measured Calculated r(461) / *■ " P°*^' 33°4r ^ ' t P - 75 33 75 32 It has not been thought necessary to give the means of the an( as measured, for the other fortns, since they agree in eveiy case, wi a few minutes, with the accepted values, using the co-ordinate Po = q 0-5376 or the axial ratio a: c = 1: 05376. Min. notet, Ser. I, U.S. Ool. Surv.. Bull. No. 490, p. 9. MINRB.VI-CXiY or M.S(K LAKE AHEA. 59 lich also !ibow> rystak. ReddMh- brown re commonly I the possible 'bserved as a t' on brown- trved as very il chron . pit. io!d!.c. f.i'cr .• een i irly w'tn the stablished. f the angles, case, within e Po = qo = It was at first thought that slight variutiuns mi«hi Ik- obscn-cd in the aagir^ of the diffcTenlly coloured crystals t\w to -» ditT*renc<' in ch' mical cmpoiiition. and with a view to testing thi^, xhv m^ans oi the angles oi (he M'Virally ailoured varieties hav» Uun as.s. w. re as follows: ColOM' of cryMaJ LUac. . . . Emenld. Yellow.. . Gdt value.. No of angles 31 63 19 p(lll) 4S»01 44 59i 45 02 45 00 .No. of ariKlcs 37M5J' 37 15| 37 16 37 14 37 112 46 t(311) _i So. of j .intileii i(312) •25J' 23} 26 59' 35' 59 34| S9 ii 22 15 1 1 il«, V :|8 i9J 59 32 — 18 26 40* 23 J' 40 23 40 22 The results are ( .f a negati\e character, since tiie differtnc'-s ob.serveil between the corresponding angles for tti.- severally ailoured varieties are (^nl> of the same order as those met with in a number of crystals of the same colour. As wall have appeared from the foregoing description, however, it would seem possible that the siight differences in composition, which have given rise to the several colours, have at least been sufficient to influence the habit of the crystals; in other words, the habit is, in general, constant in cr>'stal8 of the same colour and distinctly different in crystals of different colours. Chemical Compositiim. Heating at 105 degrees C. produces no apparent change in the mineral, and there is practically no loss in weight (about 0- OS per cent); in one instance the finely powdered material was kept at 165 degrees C. for an hour, with the same result. At a higher temperature fusion with intumescence takes place, and if the material is in the form of a powder I It cakes and turns a bath-lwick colour, losing in weight at the same time I to the extent of about 3 per cent. The melt obtained after fusion with sodium carbonate is green, indicating manganese, which is always present, though only in very small amount. The mineral is not acted on by acids. A qualitative test for chlorine and fluorine gave negative results. MUSBUH BUIXBTIN NO. 27. Several analyses were made of the lilac crystals, with the folic results: Analyses of Lilat Crystals 0/ Vesunanile. . SiO, AI.O, Fe,0. CaO MnO M 1 2 3 4 5 36-67 36-74 36-94 36-72 37-31 20-35 19-95 19-95 20-07 19- 83 1-01 0-60 0-87 0-82 0-97 37-35 37-59 37-90 0-18 0-21 0-29 2- 1- Mean 36-88 20 03 0-85 37-61 0-23 2- In each case the total iron present has been calculated as F no seperate determination was made for ferrous iron. The watei estimated indirectly from the loss in weight after heating; at 105 de C. this loss was 0-03 per cent and there was a further decrease of per cent after prolonged ignition. A second determination on am selected sample gave a total loss in weight of 3-33 per cent. The i of the above analyses is given in column 2 in the following table, specific gravity of the lilac crystals is 3-32. A single analysis of the pale yellowish-green crystals from Montreal chrome pit gave the result shown in column 3; as will be r there is a dose correspondence in the composition of the two vaiii the only essential difference being, that in the yellowish-green cr> about 4 per cent of the AUOi has been replaced by its equivalei Fe,0,. Analyses of VesmianiU. Calculated for Clarke'i formula Lilac crystab. Yellowish-gre crystals. SiO, 36-96 20-94 36-88 20-03 0-85 37-61 0-23 217 0-03 306 Vk.ftl AliOi 15-96 4-30 0-54 38-66 FeiOi FeO CaO 40-25 MnO MgO 1-25 07 311 HiO-ioS'C.::. Hrf)-H05'C.... 1-85 100-00 100-86 100-51 Analyses of vesuvianite do not, as a rule, lead to any simple for for the mineral, and specimens from different localities may vary cons ably in composition. It is, broadly speaking, a calcium-alumi silicate, in which varying proportions of the calcium may be rcpl by equivalent amounts of other metals, especially magnesium and fei MINEEALOCV OP BLACK LAKB AREA. MgO g 1 9 2-49 1-85 3 217 i 61 iron, and ferric iron may at the same time take the place of some of the aluminum. Water of constitution appears to be an essential component of the mineral, and in thirty-six analyses quoted in Dana's Mineralogy, the percenUge of water ranges from 0-55 to 3-41. Clarke> regards vesuvianite as an orthosilicate with composition essentially Ca7(OH)iAl«(Si04)., and he assigns to the mineral the constitut- ional formula reproduced below. The percentage composition calcul- ated for this formula is given in column 1 of the preceding table. SiO«I / Al— Si04" \ SiO,- rCa,: ?Ca,= ESiO, \ 3i04— Al „l, -Ca -SiO» / / Al— Si04= \ ECa. ECa, ESiO« \ ESiO«— Al / EAI, ^i^SiO. ai(Oh) ai(6h) Vtimianite Garnet Constitutional formulae of vesuvianite and garnet (aft"r Clarke). In the occurrences here described, garnet is frequently associated with vesuvianite, but at many localities in the area it is also found alone, forming dykes under conditions which suggest that its mode of origin must have been similar to that of the vesuvianite in the dykes of this mineral noted at the Montreal chrome pit and elsewhere. A comparison of the graphic formulae of the two minerals (after Clarke) is thus instruc- tive, as indicating that their molecules are very similar, both as regards composition and constitution; from this it might be inferred that the genetic relation between these two species would be very close. Optical Characters. The crystals always exhibit both the first and second order prisms; and, although one of these, usually (100), generally has a large develop- ment relatively to the other, it is possible to select crystals in which the faces of both forms have an appreciable width, and to use these as prisms, with internal angle of 45 degrees, for the determination of the refractive indices by the minimum deviation method. A series of trials, however, showed that no great degree of accuracy could be attained. This is in part owing to the fact that perfect prism faces are found only on very small crystals; the prisms used consist of two faces, of which one belongs to the form (100) and the other to (110). and it usually happens that one or other of these is extremely narrow, so that the light from a sodium flame refracted through the prism is so feeble that the images cannot be very accurately adjusted on the cross hairs. On the otiier hand, if larger crystals are employed, the images, while being sufficiently bright, are niultiple; this is the result of a feature which has already been referred ' Ctarke, F. W.. "The conMitution of the nuunl ilhcatn, ' V. S, Gcol. Surv.. Bull. 588. p. ja 62 MUSEUM BULLETIN NO. 17, to in dealing with the crystallography, viz., the faces of the prism (1 even when free from vertical striae, are in general not simple, but ( is made up of two parts inclined to one another at an angle varyini to half a degree or more, their edge being parallel to the principal of the crystal. It is possible also that the variable values found foi refractive indices may be partly due to a slight non-homogeneity in material of the crystals, such as has been frequently observed in «.ase of vesuvianite. The crystals are always optically negative, and the double refrac is weak. The average of U n fairly good determinations on the crystals gave for the refractive indices: u - 1'708, i " 1-705, and e-ui - -0-003 As an indication of the limits which were observed, the eight posi 4S-degree prisms in one crystal examined, and on which the first second order tetragonal prisms were about equally developed, j values ranging from (J - 1-70S. € - 1-;02toa» - 1-711, € - 1-709. The indices of the emerald-green and yellowish-green crystals fall within these limits, and approach closely to the above mean val from which it would appear that the effect on the refractive powe their slight differences in chemical com|x>sition is not very pronoun Although it has not been possible to determine the refractive ind very exactly, the results are sufficient to show that the crystals hav« appreciably lower refractive power than is usual in vesuvianite, this is no doubt owing to their relative freedom from iron. The hig observed limits for these crystals ( = 1-711, c = 1-709) are Ic than the generally recorded values for vesuvianite, which range f to - 1-712 to 1-732 and e = 1-7108 to 1-726; although Iddings' qu one exceptional case in which green-brown crystals from Sandford, Ma were found by Hlawatsch to have the values w = 1 • 705, € =1-701. each case the refractive indices given above refer to yellow (sodii light. Examined wirh the dichroscope, the crystals exhibit a notice; pleochroism, which, although weak, is fairly well marked in the stoi crystals; this is as follows: Colour of crystals. For light vibrating along horizontal axis (wi. For light vibrating ak vertical axis (f). Lilac Emerald-green Clove-brown pink bottle-green deep brown colourless bluish-green paler brown I Iddingi. J. P.. "Rock mimrula." IUU6. p. J78. MINBKALOCY OF BLACK LAkt AgEA. ZIRCON. A few scattered crystals of zircon were observed on specimens, from the old Standard mine, of the new mineral, colerainitt, which is described on page 66. The crystals, measuring 2 mm. in length by 1 mm. in width, have a reddish-brown colour, and a brilliant lustre; they arc t-imple combinations of the second order prism, a(lOO), with the first order pyramid, p(lll), and in most cases they are doubly terminated. EPIDOTE. Epidote occurs only as a secondary rock constituent, being especially abundant in some of the diabase masses. TOURMALINE. A few specimens bearing crystals of tourmaline were collected from the dump at the old Standard mine. These specimen*, doubtlcs.s came from a pegmatite dyke, and they consist mainly of plagioclase, optically near albite, with a little muscovite. The flakes of muscovite measure up to one cm. in diameter and are much contorted; microscopic crystal* of reddish-brown garnet are also present, especially in the vicinity of the mica. The tourmaline has a greenish-black colour, and the largest crvstaJ observed measures 4 mm. in width, by 1 -5 cm. in length. The crystah. were not measured on the goniometer but by inspection they are seen to be trigonal prisms, heavily striated along their length, terminated by the rhombchedron. HYDROUS SILICATES. SCOLECtTE Scolecite was reported from this area as long ago as 1890, in which year the Annual Report of the Geotogical Survey' refers to a specimen from "Black Uke, township of Coleraine" as having been presented to the mineral collection by Dr. J. T. Donald. The foltowing description of these specimens is given by Robert H. Jones': "In one of the granulitic d^kes on the Glasgow and Montreal Company's property. Professor Donald found and sent to me a sample of scolecite, which occurs in transparent glassy needles, filling minute veins, and in masses of white, grey, and colourless radiating fibres." A specimen collected in 1913 by Robert Harvie from the Glasgow pit of the British American Asbestos, now the Asbestos Corporation, was identified by one of the writers as scolecite. The mineral occurs « Gtol. S«ry.. Cm., Ann. R»pt., vol. V. pt. I. 1890-J. p. 68A. CtB*y LodETOOd ud Son, Uadoa. 1S97. p. IJO. •• MVSBl'M BUU.ITIN NO. 27. lining narrow fieeures in an aplitic rock, and has the form of slen prinnatic crystals arranged in divergent groups; they attain a size 2 cm. in length by about 3 mm. in width, but are commonly narroi than this, and they have a silky lustre. Examined under the microsa the crystals are found to be biaxial, negative, with weak double refracti and the extinction angle, Bx, A c-axis, was measured as 1 7 degrees. MICA. The minerals of the mica group are not at all common in the ai either as constituents of the principal rocks or otherwise. Biotite occasionally present in some abundance in the granite, but in gene this rock is essentially bnrnblendic and contains no biotite. A bro coloured mica is associated with the colerainite at the old Standi mine, and specimens of a tourmaline-bearing petjmatite from the dui at the same mine carry crystal flakes of muscovite (damourite). CLINOCHLORE. Clinochlore is fairly widespread, and sometimes occurs in v< sharply defined crystals, as for example at the Montreal chrome j These crj'stals are tabular in habit, quite transparent, and have a d< bluish-green colour by transmitted light, the tint being paler in the thini crystals; when extremely thin they are colourless. More commonly 1 mineral forms irregular deavable masses, with colour varying from grc to white, and these at times display a massive or compact structure. The best crystals collected have a width of 1 cm. or less andi not more than 2 mm. in thickness, though poorer and opaque cryst of larger size occur. In form they are six-sided plates with bevell edges; the base has the usual pearly to vitreous lustre, is usually fain striated parallel to its edges, and is seldom sufficiently flat to yield single-image reflection. The faces of the other forms are also found examination to be, for the most part, very imperfect; occasionally crystal will display between the two basal planes one or more faces whi are perfectly sharp and have a high and somewhat greasy lustre, but generally happens that these planes are heavily striated, have a d lustre, and yield continuous strings of images when examined on the reflei ing goniometer. Some crystals exhibit as many as six of such imperfc planes lying in a zone; but owing to their character and also to the fa tliat most of the crystals are lound, both by the presence of reentra angles and by optical tests, to be repeatedly twinned, it has not be possible to determine these forms with accuracy. The following fori Kcem to be well established, however, as occurring on crystals from t Montreal chrome pit. c (001) u (227) M (Tl2) t (043) ' (101) d (225) V (132) y (205) m. (112) $ (0-1 1-24) f (401) n (225) ' fine grained, although under a higi power the material is seen to be similar and to display the same rac arrangement. Within this, the clay-like substance is dispersed as du particles, or in blotches and streaks, and it is found especially at centres of the circular radial groups of crystals. Throughout the fi grained material, also, there are many more coarsely crystallized pate and veinlets, representing small druses and crevices within the r which have been completely filled. The following analyses of the matrix (column 1) and crys (column 2) were made by M. F. Connor: Analyses of CoUraiuite. Matrix Crystak Molecular ratio Percentage c position, calc ated SiOi 26-98 16-10 0-22 None 36-56 0-12 0-28 0-20 19-91 24-40 22-77 0-45 Not det'd 32-70 0-10 0-30 0-09 19-63 406-6. .2 223 2\ , 3-0/-* 25-42 AljOl 21-61 FeiOi FeO MgO 817-5 2-0 40 1-0 ,-•4 CaO 33 90 (NaK)iO MnO H,0 1090-5... 5 19. 07 100-37 100-44 10000 The mineral is thus a liydrated magncsian aluminous silicate, the case of the crystals the molecular ratios approximate to 4MgO.Al 2SiO|.5HjO and the percentage composition calculated for sue compound is given in the last column above. The calculated va are in fair agreement with those gi\en in the analysis, and the forti 4MgO.Al,08.2SiOj.5HiO or H.MgjAlSiO, is, therefore, adopted colerainite. The massive character of the matrix naturally renders it imposs to be certain that the material selected for analysis was free from for admixture, but the analysis at least serves to indicate that it has es« MimiiALocv or black lakb ansa. «» ally the same composition as the crystals. The approximate composition of the matrix, as calculated from the analysis, would be near bMKO.AUO*. 3SiOi.7H|0; if it is composed in part of colerainite of composition 4MgO.AI|0|.2SiO|.5HtO, it is necessary to assume the presence also of some admixed hydrous magnesian silicate, near serpentine. Colerainite may be regarded as a basic orthosilicate, with the constitutional formula shown below; it may be compared with newtonite' from which it differs in having the two monovalent radicles (MgOH), in place of two hydrogen atoms. SiO,^=^(MgOH)^H siO.^^H, AI-OH AI^H OH \h Colerainite Newtonite When heated at first gently to dehydration, and then strongly in the blowpipe flame, the mineral whitens, disintegrates, and falls to pieces, showing a tendency to exfoliate, and finally it fuses with littk- or no intumescence to a white, rather lustreless, glass. Moistened with cobalt nitrate and heated, the mass becomes blue. Heated in a closed tube, the mineral whitens, decrepitates, and flies to pieces, and at a high temperature gives off much water. It is decomposed with difficulty by hydrochloric acid with separation of flocculent silica, but apparently without going entirely into solution. The behaviour of the compact matrix is similar, with the exception that it does not fall to pieces to the same extent on heatii.j;, and as a consequence it appears to fuse more easily. In some specimens, the crystals are in part covered with a later deposit of a cream coloured amorphous substance, which has the lustre and rather the appearance of polished meerschaum. In one specimen collected, two nearly adjacent druses, which are lined with crystals of colerainite, are partly filled with this material, the flat surfaces of the deposits in the two druses being parallel to one another. This material was not analysed. It has a hardness rather below 3, and the specific Kravr> is 2-45. Thin splinters fuse quietly in the bunsen flame to a .vhite opaque globule, and the substance becomes pink when moistened HitJ! ci.balt nitrate and heated. ^..olerainitc was observed at only one other locality in the area, spt imens ha » ii.g been collected on a dump near the Union pit. from which they iioutidcs- came. The specimens have the same botryoidnl form as Hose Irom ; i. old Standard mine described above, but they are not nenrly =s wfii crystailized. The botryoidal spheres vary in diameter ' C irkr - .V "The coutimtion of tbt- natural nUcatct;" U. S. Gcol. Suit.. Bull. Na SM. MM. MIJSBVM BVLLtTIM NO. IT. from one-eighth to half an inch ; they are compodcd of compact materii with only a very thin, imperfectly cry»ta!line crust on their surfat No individual crystal flakes were observed on any of the specimens, b the crust was identified with certainty as colerainite, by its optic characters. Much of the compact matrix is white with a surface recalling ungiaz porcelain, as in the old Standard mine specimens, but here it shows greater tendency to concentric banding. Immediately adjacent *o t crystalline crust the material is commonly translucent and n<;ai colourless, and thiti zone is followed by banding in white, pale crea and pink. Altogether, the specimens have very much the appcaia iCC banded chalcedony and at first, indeed, they were assumed to be tl mineral. The lustre is either dull, like that of chalcedony, or waxy, li common opal. The hardness is 2J to 3 and the specific gravity, as det( mined on several pieces by the heavy liquid method, is 2-34-2-3S. The compact material, with as little as possible of the crystalli crust attached, was analysed by M. F. Connor with the result given column 1 below. Union pit Loganite, Calumet (alls Pseudqphite, Berg Zdjar SiOt 33-00 13-12 Trace 35-30 Oil 015 2-55 16-12 33-28 13-30 1-92 35 50 |l600 33 -U AliOi 15-42 FeiO, FeO 2-58 CsO MbO 34-04 \w.... ...:..:. NaiO H(0-108* H*O+108* 12-68 100-35 10000 98-14 This analysis differs from those of the old Standard mine matei mainly in showing a higher content of SiOj and lower AUOi. Th( can be no doubt, however, that this material is closely related to tl which forms the matrix of the old Standard mine specimens, and it very probable that in both cases it is not a homogenous mineral. T composition, as calculated from the analysi.s, is roughly SMgO.AU* SSiOt.9HiO; if it is assumed that the material analysed was in pi colerainite, then this might have been mixed with a hydrous magnesi silicate of composition 4MgO.3SiOj.4HjO, near serpentine, or "aph dite," which approximates to MgO.SiOj.HjO. In its blowpipe ch acters and behaviour towards hydrochloric acid, the Union pit mater resembles that from the old Standard mine; this further suggests 1 essential identity of the two occurrences. HINEIALOCV or BLACK LAH ARBA. 71 The analysis of the original loganitc' is reproduced in column 2 above, and it is interesting to note the close a)rrcepondcnce in composition between this and the Union pit material; the SiO|,AI|Oi,and MgO content is almost identical in the two sulMtances, but loganite contains appreci- ably less water and further has nearly 2 per cent FetOi, whereas the other is essentially free from iron. The resemblance between the two sub- stances ceases here, however; they arc widely different in their physical characters, loganite being descrilied as follows: "Hydrated aluminous magnesian minerals, sparry in crystallization are met with in several localities among the Laurcntian limestone in Canada. The first one to be mentioned occurs at the Calumet falls. It is associated with pale green serpentine, brown phlogopite, and apatite, in a white crystalline lime- stone, and has been described by the name of loganite. It occurs in short thick oblique rhombic prisms, replaced on the edges or on the acute solid angles. The crystals arc generally rounded, but present a prism of 124 degrees, or near to that of hornblende. There is a distinct cleav- age with the sides and the base of the prism, and an imperfect one with the longer diagonal. The hardness of the mineral is about that of calcareous spar, and its specific gravity is from 2 -60 to 2 -64. The surface of the crystals is dull, but the lustre of the cleavages is vitreous and shining. The colour is dove-brown or chocolate-brown, and the mineral is sub-translucent, brittle,, and with an uneven fracture. The crystals, which are seldom more than one-fourth of an inch in diameter, are penetrated by carbonate of lime, from which they are with difficulty freed. The mineral is infusible before the blowpipe, and partially decomposed by acids. . . . The composition [in the analysis reproduced above] is calculated for 100 parts, excluding the carbonate of lime." Loganite is generally regarded as a member of the chlorite group of minerals, and, more particularly, as a variety of penninite. It is nearly related to, or identical with, pseudophite, which has a very similar composition, but contains 2 or 3 per cent less water (see analysis in column 3 above). Pseudophite, which occurs as.sociated with enstatite at the Berg Zdjar in Aloisthal, Moravia, and elsewhere, is described' as being a compact massive substance, without cleavage, which resembles serpen- tine (whence the name from noevios false, and ophite or serpentine); H = 2'S; sp. gr. = 2'75-2-77; lustre, weak; colour, greyish-green, olive- green, pistachio-green; feel, unctuous. The present material thus somewhat resembles pseudophite in its general physical characters, except as regards colour and specific gravity, but it contains considerably more water. ■ G»l. of Can., 1«63, p. 490. • Oua. Mlncrakxy. 6th otitloii. p. 6S1. MICIOCOPV RESOIUTION TBT CHART (ANSI and ISO TEST CHART No. 2) M2a 14.0 2^ 2.2 l2 I 1.8 jA .APPLIED IM/OE Inc 1653 East Main Street Rochester, New York U609 USA (716) 482 - OJOO - Phone (716) 2Ba-59e9-FQ» 72 Munm ■inj.mN ho. it. In view of the very compact and almost amorphous condition of t material from the Union pit, and also to a lesser degree of tlie matrix the old Standard mine specimens, with the consequent uncertain as to the constitution of the material selected for analysis, it has not be deemed advisable to assign special names to these substances. Ev in the Union pit spedmcnfi, which have an extremely compact structu like chalcedony, it is usually possible to see some small glistening flakes colerainite distributed through the material, and sometimes these a arranged in very narrow streaks. When crushed and examined in < under the microscope, the fragments are found to be all perfectly trar parent, with low index of refraction, and for the most part they a weakly birefringent with a concentrically banded spherulitic structur occasionally also, a flake is found which gives the uniaxial positive intc ference figure. Other fragments, however, appear to be perfectly isotrop and amorphous. It is believed that the crystalline material is in s cases colerainite, and that there is probably associated with this son amorphous hydrous magnesian silicate, perhaps also aluminous, < indefinite and possibly variable composition. In some cases the latt may have a composition approaching that of pseudophite or loganit and in others near serpentine. Although the colerainite specimens, both from the old Standai mine and also from the Union pit, were collected from dumps, and tl material was not actually seen in place, it doubtless originally forme veins traversing the massive serpentine in each case; and, judging by tl size of the specimens, especially those on the old Standard mine dumi these veins must have had a width of 2 or 3 feet at least, and may haA been very much wider than this. As has already been stated, examinatio shows that this vein material is composed almost entirely of colerainit alone, with probably some associated amorphous hydrous magnesia silicate. The mode of occurrence would thus be very similar to that < the veins or dykes composed of other minerals, such as diopside an yesuvianite, which have been noted at several localities and describe in earlier pages, ?nd it is believed that the colerainite veins have originate in a similar way to them. The conclusions arrived at by the writei regarding the genesis of these various mineral veins have been set fort in a section dealing with the origin of the minerals (page 10). Briefl stated, it is believed that the extremely acid and aqueous granitic magm which formed the last phase of intrusion of the it neous rocks of th serpentine belt, acted as a powerful solvent on the basic rocks as it wa injected through fissures traversing them; this solvent action bein largely due to the extreme difference in chemical composition betwee; the magma and die invaded rocks. As a result, the magma, or th magmatic residue, was enriched in certain constituents derived froB HINMALOGT OT BLACK LAKE AKBA. 7| theae rocks, and, on crystallization, it formed dykes or veins of such minerals as diopside, grossula'-ite, and vesuvianite. Present observations indicate that veins of these minerals, containing high percentages of lime, are of more frequent occurrence in the chromite pits than elsewhere; that is, they are associated with a rock which was originally near pyroxe. nite in composition, and which contained an appreciable amount of lime. It is believed that the genesis of the colerainite veins is to be explained in a similar manner. In this case, however, a hydrous silicate of alumi- num and magnesium has been foimed, containing no lime, and it is interesting to note that colerainite has been found only at asbestos pits, where the original country rock was a peridotite, containing little or no lime. SERPENTINE. Serpentine is the mineral most commonly met with in the various quarries and pits of the area. In its fibrous form, chrysotile-asbestos, it constitutes a product of great economic value. Several other varieties of the mineral occur and are described below, but they are only of miner- alogical interest. Mode of Occurrence of the Massive Serpentine and Chrysolile. Full descriptions of the mode of occurrence of the massive serpentine and chrysotile in the area may be found by referring to the report of Cirkel' and more especially to that of Dresser. The outstanding features may be summarized as follows: The massive serpentine occurs within the i>eridotite masses, in the form of zones or bands, whose boundaries against the peridotite are fairly sharp and are roughly parallel to one another, i.e., they rather resemble dykes in outline, and assume all attitudes from vertical to horizontal. The' more prominent bands fall into roughly rectilinear sets, which follow the same directions as the main system of joints in the peridotite. Others, which are in general narrower and more irregular in their course, intersect these and one another at all angles, so that, in some places, the peridotite presents a remarkably intricate network of such serpentine bands. Of these minor bands. Dresser believes some follow strain fractures due to regional compression, and others, cracks caused by exfoliation. Although these bands are fairly well defined, the peridotite for some distance on each side of them is serpentinized to a fairly considerable, and gradually decreasing, degree. >Cirkd, Fittx. "Chryiotih Mhntw, itt occuncncc, exploiutioF, inUliiig, ud unt;" Cu., rapoct No. 69, 19ia 74 MUSBVM BULLETIN NO. 27. The central part of the massive serpentine bands is usually occupi by the fibrous variety, chrysotile; this also is dyke-like in shape, t, its boundaries agair:.t the massive serpentine are roughly parallel one another, and are r-ther sharply defined. There appears to be a fairly constant relation between the tot width of any massive serpentine band and that of the chrysotile vt which "t encloses. Attention was first called to this feature by Dressi who, from a number (49) of measurements, found that the entire serpc tine band is about 6-6 times as wide as the asbestos vein within it. The chrysotile fibres are all arranged parallel to one another, ai lie in directions normal to the walls of the vein. Usually the fibres are n continuous right across the vein, especially in the wider ones, but the is a parting, or sometimes more than one, at or near the middle, whi is occupied by a film of granular iron ore, usually magnetite. Carbonates of lime and magnesia occur only in very small amou in the serpentine and associated rocks of the area, either in the form veins or otherwise. Lastly, granite is frequently found in the vicinity of good asbest deposits, or, stated in another way, an accumulation of asbestos vei (and, therefore, also of serpentine bands) can very frequently be notio in approaching the granite dykes. Mode of Origin of the Massive Serpentine. As has already been stated, the principal rock of the serpentine bj in the Black Lake area is peridotite, or a rock intermediate between tli and pyroxenite, and it is generally agreed that the massive serpentii has resulted from the metamorphism of this rock; it is further believ* that the serpentinization commenced along joints and other cracks, fro which it proceeded outward in opposite directions. Field evident points to the joints being more or less contemporaneous with the grani dykes; in other words, the rocks were shattered during the last phas of igneous activity, joint systems were developed, and along some of tl fissures so formed, the granitic magma was injected. This correlat the commencement of the change from peridotite to serpentine with tl period of granitic intrusion, or some time subsequent thereto. While the actual source of the serpentine is thus well establishe there may still remain some doubt as to the mode by which the chanj has been brought about. The production of serpentine from olivii involves, in general, either an addition of SiOj or a removal of Mg< in addition, of course, to hydration. If the reaction was of the first typ siliceous waters would supply the necessary reagent; in the second t>'p the excess of MgO must enter into some new form of combination, sue as carbonate, in which case it would be necessary to asume that tl MINBRALOGV OF BLACK LAKE AREA. 73 solutions producing the metamorphism were charged with COj. These two types of serrentinization may be represented by the equations (1) 3Mg,Si04 + SiO, + 4H,0 (2) 2Mg,SiO« + CO, + 2H,0 2H4MgiSi,0. H«Mg,Si,0,+MgCO,. If the metamorphism takes p' .- -- through the agency of siliceous waters, serpentine is the only product necessarily formed, with perhaps some iron oxide (magnetite) if the olivine of the peridotite is an iron- bearing variety; but serpentinization by means of carbonated waters necessitates the simultaneous formation of a considerable amount of magnesium carbonate. Since the rocks of the area are free from carbon- ate, except in very minor amounts, the evidence points to siliceous and not carbonated waters a^ the reagent which has been responsible for the serpentinization. There yet remains the question as to the source of these waters, whether they were of meteoric or magmatic origin; and here again there is no certain proof for either of these alternatives. The field evidence, however, points to a connexion between the granite dykes and the amount of serpentinization ; and it seems most probable that the metamorphism was brought about by magmatic solutions which accompanied the injection of these dykes, or which wer» not required in the composition of the dykes and were expelled as the laUer consolidated. Mode of Origin of the Chrysotile. Various theories have been advanced to explain the origin of the chrysotile veins, and references to the literature dealing with this subject will be found in the reports of Cirkel and Dresser. It will be sufficient to reproduce here the conclusions arrived at by the latter author as the result of an ex .ided examination of the district :' "The position, size, and number of asbestos veins in rich ground, make it inconceivable that the spaces they now occupy were once open fissures, and especially that many of them were open at the same time. Open fissures up to 2 inches in width, running in all directions from vertical to horizontal, extending 100 feet or more in length, and occupying in places as much as 10 per cent of the entire rock, would be a mechanical impossibility. The possibility remains of crevices having been enlarged and filled by replacement. "But the asbestos of the veins is practically identical in chemical composition with the serpentine of the walls, which is strong evidence against the material composing the veins having been brought in either from above or below. Segregation from the walls also would imply a difterence in chemical composition, which does not exist. In other ■Op.clt.,p. "'ii- IT. Cmnparisom vilh Russian Deposits. A very ck»e resemblance between the mode of occurrence of chryiotile^isbestos in Quebec and in the Urals is indico ed by the ( lisher* dtscriptions of the latter deposits, and the following notes cono ing t.-cn Hre of interest as affording a con.parison of the two.' The Russian deposits are situated about 80 miles northwet< Ekaterinburg, where serpentine and allied rocks form a belt 2 to 3 n wide, extending for 30 miles with a very regular north and south tr( The rocks of the belt lie wholly within granite and they consist of cl itic and talc schists (in places carrying emeralds and other gei diabase, porphyrite, and serpentine. The serpentine forms a at of elliptical masses with their longer axes running north and so parallel to the trend of the belt, and one of the largest of these mt is a mile long by about 1,000 feet wide. Some narrow portions of belt consist only of diabase and porphyrite, and veins (dykes ?) of latter traverse the serpentine in places. As in Quebec, the aslx is mainly in veins of cross fibre, and tiese attain a width of as muc 8 inches; but there is also some fibre, up to a yard in length, run parallel to the fissure walls. The associated minerals are stato include magnetite, well crystallized, in veins and small aggregi garnet, including grossularite, ouvarovite, and andradite; vesuvia sometimes emerald-green and chromifcrous ; chlorite; crystalline qu chalcedony, and rarely milky opal; and occasionaly aragonite ai calcium-iror -magnesium carbonate. The writers have not been able to obtain any information regai the actual mode of occurrence of these minerals in the Russian dep( but it will be observed that the mineral association is, in the main same as that of the Black Lake area; the most notable difference the absence of diopside from the Urals and the occurrence the quartz, chalcedony, and opal. It may be added, however, thai matrix of the colerainite on the specimens from the Union pit so cl resembles chalcedony or common opal t*iat the specimens collected at first wrongly labelled as such. As an additional point of resemblance between the Quebec Russian asbestos deposits, it is interesting to note that, in the descri of the latter, as given in the abstract referred to, no mention is ma the occurrence of limestone in association with the rocks of the s ;rpe belt. > KfyiteMtet oonotTB- I lorthwest oi 2 to 3niilM south trend sist of chlcr tther gems), nu a waieu I and soutk, these maaiKMi rtions of thr kes ?) of ike the asbestok f as much a* gth, running re stated to I aggregatCK, vesuvianitp, alline quartc, {onite and t ion regarding sian depodts. the main, the ifferences are cnce there ol ver, that the pit so closely :ollected wtre Quebec aad he description ion is made tt the s ;rpentioe TOl. XT. WM EAOUN. Kaolin occurs •pwingly in some of the rocln, m an alteration product of the fetdspar. Tltano-Slllcata. LBUCOXENB. The diabase which occura in the area is, aa a rule, very much altered, and leucoxene forms one of the secondary products usually present. Phoaphata. APATITE. Specimens bearing well crystallized apatite were obuined about 5 miles northwest of Black lake, near the road leading to St. Ferdinand de Halifax. They were not found in plaz-e, but in some boulders used in the construction of a stone fence, anu their original location has not been traced. The first, and also the finest, specimens received by the writers, were collected in 1912 by D. A. Niail, of the Geological Survey, whose attention was attracted to the boulders by .some bright quartz crystals they con- tained. The quartz crystals in these boulders had been observed prior to thi'j by Mr. A. Nadeau, of Black Lake, who, at the suggestion of R. Harvie, collected a numtx^r of specimens for the Geological Sur\cy. The locality was later visited by one of the writers. The boulders, which are in many cases cavernous or drusy, consist mainh ot massive white quartz, and have doubtless, come from some quart? or p*gma >tic veins in the immediate vicinity. A considerable amount s mira i ,(nall scales, more or less altered, is sometimes present, especially in tr averiu-us Ixnilders, and, associated with it. are pyrite and siderite (p.^* 24), Ixith in small amount, together with their alteration pi dii. ! a soft earthy limonite with which the druses are more -n this (i p< If is removed, the walls of the cavities ■<\\ crystals of colourless qu.irtz, usu y small, =.- a length of one centimetre; these are described flh^pection shows that many of "^he quartz crystals crystals of colourless, transparent apatite, which, in turn, rest on the m. -sive white quartz, indicating that the apatite crystals are later than the rr ivc quartz, but older than the quartz crystals. Owing to their »iner i,4 occurrence, it was not possible to remove any complete crysui * apaf)t<< from the specimens; nevertheless, a considerable amount =a«teria was > i/tained, consisting of partially broken crystals, but enua*^ •' suxaUc for goniometric measurement. or less filled. " are found tfi but sometime on page 15. f are superpo^e{i u 12 NVnUM BUIXniM NO. It. The crystals, which, as already noted, are perfectly colourless a- n.insparent, are mostly very minute, but some measured up to oi centimetre in diameter. The habit is invariably tabular parallel to tl base, and the crystal plates are quite thin, even the largest crystals n< exceeding 2 mm. in thickness. They are generally doubly terminate Irregularities on the basal . lane in all the crysUls measured indicate th; parallel growth is very prevalent. Owing to the habit, the basal pinacoid is by far the most prominei form on all the crystals. Otherwise, they are of two types, ch-— >.ctc. izi in general by the presence or absence of the prism of tl -it ord« m(lOlO). In the first type, the principal forms presenj, ' u lition the basal pinacoid, are the prism of the first order m(10lO; ..U the ti pyra nids of the second order s(n21) and /(1 122). Other forms not on vh; ^ crystals, in the order of their relative development, arc ihc fii order pyramids. y(2021), xOOll). and r(1012); the third order pyrami( ;i(2131), n(3141), and o(3142); and the third order prism, h(2130). addition to these, the firs* order pyi imid, a(3032) was noted as sm faces on some of these crystals. In the second type, the largest form, after the base, is the fi order pyramid, r{10l2); the second order prism, a(1120) is present narrow faces, but the first order prism is lacking. A complete list of forms observed, together with the measured a calculated angles, is given belov : Crystal For fA^Hk. Letter 1 1 Syi.-.ojl 1 1 Mcasurc : 90' 00' 22 57 40 16 51 48 59 27 36 16 55 43 71 52 56 47 • 65 57 ' "-'^; ■ Museum Bulletin No. 27. 85 Plate III. Granitic intrusion in peridotite, grossurlaite is found at the contact; Hall chrome pit, Thetford quarry of the Dominion Mines and Quarries, Limited. (Page 48.) 87 Ml'SEUM BULI-KTIN No. 27. 89 in. ATE V. Chromite pocket of Hall chrome pit, Thetford quarry;^ of the Dominion Mines and Quarries, Limited. (Page 17.) St' ti'F '}\ MrsKi M Hi IIKTIN No. !'■ 9J Pi.ATK vri. The main Montreal chrome pit, showing chromite pockets. (Page 19.) •5 I * L i 7" c i ~. ^ ~ 3 m'i Mt!>KrM Hii.i.KiiN No. n. VI Platk IX. A. A. and B. Microphcitographs of ropes of garnet In feldspar in a garnctlfcrous aplitc, magnified 30diamctfrs, it;ilural IIkIiI; Caril;Tni ohrome pit. t!'.ii.t -'•0.) ML'SEL'M Bl'LLETIN No. 27. 99 Platk X. /r '■"1 Sggg* N \ ^^ - ^^^^Bk -'""^"^-^r, 1 1 'v- '*■■• ■4 .}i f " 1- 1- B. A. Microphotograph of radiated vesuvianite with dioixside, magnified 30 diameters, natural light; Montreal chrome pit. (I'agc 52.) B. MiiTophotograph of radiated vesuvianite with dio|>side, magnified 30 diameters, polarized light, Montreal chrome pit. (Page 52.) MisEi M Bri.LKTiN No. 27. tot PlAlE XF. A. MIcrophotograph showing .Iriisv character of colerainite-Uuiring rm-k, maBnitipcl 30 diameters, natural hght ; Standard asl)eslos mine. (Page 67.) B. Microphotograph show-ing driisy character of colerainite-l)earing rock, magnified 30 diameters, ix)larized hght; Standard aslx-stos mine. (Page 67.) Ml SKI \i Bi i.i.KiiN Ni). >7. KM Plate XII. ^irifek^ c. MicrophotOKraphs of aggregates of wcdge-shafx-d .■olerainlti' crvslals; Standard aslicstos mine. Note lines piirallel to the l)ase of the wedges. (Page 67.) .A. Magnified 50 diameters, natural light. H. Magnified 50 diameters, polarized light. C. Magnified 100 d imeters, polarized light.