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HUNT, OF THE GEOLOGICAL COMMISSION OF CANADA. ^T^HE oldest known group of rocks in North America is that A to which the name of the Laurentian System has been given in the Reports of the Geological Survey of Canada, and is made up of very much disturbed and highly crystalline strata, which are in great part gneissoid and quartzose. Interstratified with these, however, are beds of crystalline limestone, often of great thickness, and holding scapolite, pyroxene, phlogopite, ser- pentine, fluor, apatite,, spinel, corundum, condrodite, sphene, graphite, and other characteristic minerals. Associated with these limestones, there is another rock forming an important member of the group, and consisting chiefly of felspar, with small portions of black mica, green pyroxene, and occasional grains of garnet, epidote, and more rarely of quartz. This rock is often marked by the presence of small portions of hypersthene ; from the presence of this mineral, these masses have been described by the New York geologists as hypersthene rock. In addition to these minerals we may add ilmenite, or titaniferous iron ore, which occurs sometimes in large masses, and at other times in 2 Mr. T. S. Hunt's Examinations of some Fehpaihic Rocks, small disseminated grains, which like the hypersthcne appear ta mark the planes of stratification. If to these we add small por- tions of iron pyrites and a little disseminated carbonate of lime, we have the mineralogy of the rock so far as yet known. The texture of these felspar rocks is varied; sometimes the mass is a confusedly crystalline aggregate, exhibiting cleavage surfaces three or four lines in diameter, with a fine-grained, aomewhat calcareous paste in the interstices. Sometimes the whole rock is uniformly granular, while more frequently a gra- nular base holds at intervals cleavable masses of felspar, often several inches in diameter. The colours of these rocks vary from grayish and bluish-white to lavender and violet-blue ; flesh-red, greenish and brownish tints arc also met with ; the colours are rarely brilliant. These felspars seldom occur in distinct crystals, but their cleavage i» triclinic, a fact which, coupled with their densities varying from 2'66 to 3*73, shows them to belong to the group of which albitc and anorthite may be taken as the representatives. The bluish cleavable vai-ieties often exhibit the opalescence of labradorite, to which species American mineralo- gists have hitherto referred them ; but with the exception of a few analyses by myself, we have no published analyses of any of these felspars. My investigations show, that while all of them are felspars with a base of lime and soda, the composition varies very much, being sometimes that of labradorite, andesine or in- termediate varieties, and at other times approaching to that of anorthite. The results of these examinations, as far as yet com- pleted, I propose to give in the present paper, as the first part uf the history of these felspathie rocks. One of the ' jost interesting localities of these felspars is in tl^e parish of Chateau-Richer, in the county of Montmorenci near Quebec, where they cover a breadth of two or three miles across the strike, bounded by crystalline limestone on one side, and a quartzo-felspathic rock on the other, and rising into small hills. In this region several varieties of the rock appear, but the most interesting is made up of a finely granular base, greenish or grayish-white in colour, holding masses of a reddish cleavable felspar, which are sometimes from one-tenth to one-half an inch in diameter, but often take the form of large imperfect crystals, frequently 12 inches long, and 4 or 5 inches wide. These dimensions correspond to the faces M and T, while the face P, characterized by its perfect cleavage, is from half an inch to 2 inches broad. Twin crystcls sometimes occur having a compo- sition parallel to M. Hypersthene is met with throughout the rock in flattened masses, which although variable and irregular in their distribu- tion, exhibit a general parallelism ; they are occasionally 4 or Mr. T. S. Hunt's Examijiations of some Felspathic Rocks. 3 5 inches in length and breadth, by an inch or more in thick- jss, and are separated from the granular felspathic rock by a thin film of brownish-black mica. Titaniferous iron ore is also found in grains and lenticular masses, occasionally an inch or two in thickness ; these occur in the granular base, and gene- rally near the hypersthene, but grains of the mineral are ooca- sionally found in the crystalline felspar. Quartz in small grains IS imbedded in the titaniferous iron, but was not observed else- where in the rock, nor have any other minerals than these been detected. In the specimens of the rock which I selected on the spot for examination, the crystalline felspar constitutes from one- half to seven-eighths, while the hypersthene does not equal more than yf ^dths, and the titaniferous iron more than y^^dth of the whole ; the amounts of quartz and mica are insignificant. In other portions of the rock, however, the proportion of the ore may equal 5 per cent., and in some parts the amount of hyper- sthene is nearly as great. By the action cf the elements, the surface of the rock becomes of a dull opake white ; the cleavable masses of felspar are, however, less affected than the granulai- portion, and by their obscure reddish colour are distinctly visible on the weathered surfaces ; this change extends but a very little distance into the rock. Tho iron ore of course remains unaltered, but the dark brown hypersthene becomes lighter, and inclines to a pinchbeck-brown. The felspar is triclinic in cleavage ; the angle of P : M = about 80° 80'. Cleavage with P perfect, with the other planes distinct; P is often delicately striated, and sometimes curved. Hardness = 6, and density 3'667 to 2-674. Lustre vitreous, sometimes pearly on P; colour flesh-red, passing into reddish, greenish and grayish-brown; the surfaces sometimes mottled, but the red always predominating. The following analyses were made of three different specimens, which were carefully selected, and after being pulverized, dried at 213° F. The earthy ingredients were determined after fusion with carbonate of soda, and the alkalies by the method of Dr. J. L. Smith, which consists in igniting for some time the finely levigated mineral with five or six parts of carbonate of lime and three-fourths its weight of sal-ammoniac. The agglutinated mass slakes by the action of water, and yields to that liquid its alka- lies in the form of chlorides, with a mixture of chloride of cal- cium. A second ignition of the undissoved residue with two- thirds the first amount of sal-ammoniac ensures the separation of the last portions of alkali. These processes were adopted in all the analyses here given, with some exceptions to be noticed in their places. 4 Mr. T. S. Hunt's Examinations of some Felspathic Rocks. I. II. III. Silica .... 59-55 59-85 59-80 Alumina . . . 25-62 25-55 25-39 Peroxide of iron . •75 •65 •60 Lime .... 7-73 6-94 7-78 Magnesia . . . traces •11 •11 Potash .... •96 -96 1-00 Soda 5-09 5-09 5-14 Loss by ignition . •45 -30 •00 100-15 99-45 99-82 In another specimen the amount of lime was foimd to equal 7-89 per cent. The composition of this felspar is very nearly that of andesine, which, according to Abich, yields silica, 59-60; alumina, 24*18; peroxide of iron, 1-58; lime, 5-77; magnesia, 1^08; potash, 1-08; soda, 6-53 =99-82. The greenish base of the rock is generally finely granular and strongly coherent ; the grains possess the cleavage, lustre, and hardness of felspar ; the density of carefully chosen fragments was from 2-665 to 2-668. The greenish-white of the powder is changed to a fawn colour by ignition. When pulverized and digested with acetic acid, the mineral loses two or three thou- sandths of carbonate of lime, with traces of magnesia, iron oxide, and alumina. A portion which had been thus treated and care- fully dried gave the following results : — Silica . . . . Alumina . . . Peroxide of iron Lime ... Magnesia Potash . . Soda . . . Loss by ignition IV. 58-50 25-80 100 8-06 •20 1^16 5-45 •40 100-57 It is therefore a felspar differing but little from the crystalline andesine in composition. The hypersthene occurs in foliated masses with curved sur- faces. Besides the basal cleavages thus exhibited, it cleaves readily with the sides of an oblique prism of 87°, and with its longer diagonal. The hardness of the mineral is 6, and its aj b r( d( Mr. T. S. Hunt's Emminations of some Felspathic Rocks. blS-tr*V°n^tWn W^'' 'n'^"''!' '''''^'""0 ! colour powder ash-Krav thf-^Li. yellowijh-brown ; rtreak and f ubtra„sl„ef„7brittle Zl;;S^^^ had served to determine \h^ ,^ZJv^^\ "^ fragments which pathic matter bXeTthe laminf ^t" ''''^*"^°^'* ^^^^« "^ ^^l^" removed in breakW un ZT^ ^^ff were, as far as possible, results of two analysfs Z fusion l^T^^'T ^""^ "°«^y«i«- The follows :— ^ ^ ^"''^'^ ^^*^ carbonate of soda were as Silica . . Alumina , . Protoxide of iron Lime .... Magnesia . . Manganese . . Loss on ignition V. VI. . 51-85 51-39 . 3-90 3-70 . 20-20 20-56 . 1-60 1-68 . 21-91 22 59 . traces •20 •10 99-66 99-98 hardness was 6, LnLTnsilv nf J fi'^ "" ^'P"™'*-!- !»» Titanic acid . . Peroxide of iron . Magnesia . . . Insoluble quartz, &c. VII. 39-86 56-64 1-44 4-90 102-84 A large portion of the iron is to be regarded as nrotoxidp . Another variety of the lime-felspar rock from Ch^/tp!,?P^' i buf ;ixr L'S^^^ Th?:^r; ^-i^— P^n the dea'vage ; density of the greenish-gray portion was 2-681: an'dt'nalys'^ 6 Mr T. S. Hunt's Examinations of some Felspathic Roch. VIII. or . . . 55-80 ?\ na' ■*'... 261)0 Alumina -„ Peroxide of u-on . . • • ^ ^^ Lime .gy Magnesia .g^ J"^^'*^ ; 4-77 Soda ...••• .^g Loss by ignition .... __ t " "''";tuhtXc ' The\ eta Zt^y g.-anula.. felspar been met with in piacc. xn vitvoous lustre, exhibiting of a light reddish-gray ^«^^^^' ^^^^..^^^J^-^LcWed maU everywhere distinct cl^^^^^S^/',^"^.^" "^fi^rof brownish mica. graiL of ilmenite, sui^ounded lf^^.^*^^'"^2"^^^^^ are often Ihe imbedded crystals of ^^P^^^ ^^^^^y ,^ 'i„eh in thick- 3 or 4 inches ^^.^^^g^^.l^^^^^^^^ ness. The faces of pei tect cleavage u j tlcfined, the smaller crystals which are o ten sl^^^^^^^^^ ^^ ^.g^^. are sometimes curved, "ardness o aen y, lustre, vitreous; colour, f ^jj^^^^f ^^^^^^^ escence. Semitransparent, ^ ^^^^^.^^^^^^^ bouring parish of St. Joachim. ^ ^^^ Silica .... 57-20 57-55 57-35 Ilumina . • ■ 26-401 37.10 27-30 Peroxide of iron . '40 J ^^^ Potash .... » g.gg Soda • • . • • ^ ^? .00 -25 Loss bv ignition . _y^ ^^ • 99-66 99-75 m, J- . -n* «f Montreal also affords extensive exposures ot t '=■'•""11 cLrt"; tL;t JXnT„e.g/led and ho ^V Rawaon and Cl'f '"-^ '"^xceedinirly tough rock, with an uneven iS.::rfar«reJf^^£5-^s^^ bodies of this roek are ^^^^^^l^^ZX^^^^'-^^^^'^'' '" :r i^ntrAet^^r'ai^. l^rerslith i.mSite. These layers Mr. T. S. Hunt's Examinations of some Fehpathic Rocks. 7 of pyroxene are seldom more than 4 or 5 lines in thickness, and nay be an inch or two apart, while those of ilmenite are still thinner, and often enclosed in the pyroxene, along the sur- taces of which deep red grains of garnet are occasionally seen, Ihese different minerals appear in relief upon the white weathered surtace of the rock, and give a picture of its stratified structure, which IS, however, not less apparent upon the surfaces of recent tracture. Small, rounded, bluish musses of clcavable felspar arc trequeutly disseminated in the same planes as the other minerals In some places the pyroxene appears to pass into, or is replaced by, foliated hypersthene. A homogeneous fragment of this rock from Rawdon had a density of 2-691. It was bluish-white, gra- tiular and translucent, and gave by analysis,— ^j.,. XII. ^V»ca 54.45 Alumina 28-05 Peroxide of iron .45 ^^^'^ '. '. 9-68 rotash j.qq ?"^a, •......*.*.' 6-25 Loss by Ignition .... ^ T . . , ,. 100-49 In connexion with this variety, which has nearly the compo- 81 ion assigned to labradorite, I may give the analyses of two felspars which differ from it principally in their greater amount of lime. No. XIII., from tne township of Morin, belongs to the same area as the last, and forms large clcavable masses in a fine-grained base. Its density is 2-684 to 2-695, and its colour greenish-gray, passing into bluish-gray, with an occasional pearl- gray opalescence. The greenish paste of this felspar is softer 5i 5i .^' ^""^ V^^"^^ ^^*^ effervescence about four hun- dredth? of carbonate of lime to dilute acids ; the insoluble residue has nearly the composition of the felspar. No. XIV. is a clea- yable, lavender-blue, opalescent variety, from a rolled mass found m Drummond, Canada West, and having a density of 2-697. The determination of the alkalies in this was not made by the same process as in the other analyses, and probably does not give the full amount. ^iii XJV Silica ..... 54-20 54-70 Alumina .... 29*10 2980 Peroxide of iron . 1-10 -36 Lime 11-25 11-42 Magnesia ... '15 traces Loss by ignition . '40 '40 100-00 99-35 8 Mr. T. S. Hunt's Examinations of some Felspathic Hocks. At La-Chute on the Ilivicrc du Nord, there is a felspar rock astsociatcd like the others with crystalline limestone^ and holding in a greenish granular base a cleavable felspar resembling ande- sine in composition. Its lustre is vitreous, and the face of perfect cleavage, as in all these felspars, is finely striated. Den8ity,2*G87 ; colour, lavender-blue, passing into sapphire-blue; semitrans- parent. Its analysis gave — XV. Silica 6815 Alumina 2G09 Peroxide of iron '50 Lime 7*78 Magnesia '16 Potash 1-21 Soda 5'55 Loss by ignition '45 99-89 The byto'vnite of Thompson appears to be one of these gra- nular felspar rocks, and can scarcely be distinguished from some of the varieties just described. In 1850 1 examined an authentic specimen of the mineral, and found it to have a hardness of 6*5, and a density of 2*732 ; it gave by analysis,— XVI. Silica 47-40 47-30 Alumina .... 30-45 Peroxide of iron . . '89 Lime 14-24 Magnesia .... "87 Potash -38 Soda - 2-82 Loss by ignition . 2-00 9905 I remarked at the time, the undoubted felspathic character of the mineral, which I described as corresponding to the thior- sanite of Genth^ and as probably anorthite with up admixture of quartz*. The frequent association of ilmenite with these felspars, derives additional interest from the fact, that the immense deposits of this ore at Bay St. Paul are accompanied with a lime felspar. Here, besides many smaller masses, a body of titaniferous iron ore, 300 feet long by 90 feet wide, is exposed on the side of a hill, and a still larger mass is said to occur in the vicinity. The ♦ See this Magazine, S. 4. vol. i. p. 324. Also Report of the Geological Survey of Canada for 1850-61, p. 38, where analysis XIV. has also appeared. Mr. T. S. Hunt's Examinatioru of tome Felapathic Rockt. 9 ore is coarsely crvstalline; its colour and streak are iron black, and its lustre submetallic j it affects the magnetic needle very feebly. Hardness, G; den-lty, 4-56 to 466. Its analynis gave me titanic acid, 48-60 ; j, coxide of iron, 37-06 ; peroxide of iron, 10-42; magnesia, 3-60=99-68. Disseminated through portions of the ore, are small, garnet-red, translucent grains, which have an adamantine lustre, a coiichoidal fracture, and a hardness of 6. They are found by analysis to be pure oxide of titanium, and are to be referred to the species rutile or brookitc. We have in the rocks which have been the subject of these examinations, a scries of felspars in which the amount of silica varies from 47-40 to 59-80 per cent., and that of the lime from 7-73 to 14-24 per cent., the amount of the alkalies decreasing as that of the lime augments. These results only help to confirm the conclusion which may be drawn from all the previous analyses of triclinic felspars, that there are no defined limits for those species which, like vosgite, labradorite, andesine, and oligoclase, have been created between albite on the one hand, and anorthite on the other. I therefore proposed some time since to regard all of the intermediate felspars as mixtures of these two species, which, being homoeomorphous, may be supposed to crystallize together in indefinite proportions. * Multiplying and expanding the received formulse of albite and anorthite, I represented them as follows (silica being SiO, and alumina alO = (Al« 0»)-i-3)* : — Eq. wt. Density. Eq. vol. Albite . . (Si'«8al'2Na4)0«4=1054-4-s-2-62 =402-4 Anorthite . (Si3'al24Ca8)O^=1118-4-i-2-72=405-0. The composition and density of the intermediate felspars per- mit us to regard them, for the most part, as mixtures of a soda- albite and a lime-anorthite. In the analyses of many albites and anorthites, however, we have evidence of similar admixtures ; for some albites contain from 1 to 25 per cent, of lime, and anor- thites from 3 to 4 per cent, of alkalies. Of a like significance is the constant presence of a small amount of potash with the soda of these felspars, and the magnesia, sometimes amounting to 5 per cent, in anorthite, leading us to infer the existence of lime and potash-albites (orthoclase ?), and soda and magnesia anor- thites. The difficulties presented by the vai-ying composition of these felspars are obviated by admitting such a mixture of species as constantly takes place in the crystallization of homoeo- morphous salts from mixed solutions, and this consideration should ne/er be lost sight of in the study of mineral chemistry. It was not until after I had published this view of the consti- tution of the triclinic felspars (a view which must also be ex- * American Journal of Science, 2nd series, vol. xviii. p. 2/0. 10 Mr. T. S. Hunt's Examinations of some Felspathic Rocks. tended to the scapdlites), that I became aware that Th. Scheerer had recently proposed to regard all felspars as combinations of ancrthite with labradorite, anorthite with albite (orthoclase), or labr.idorite with albite*. It was gratifying to find that this tliaunguished chemist had already arrived at a solution of the problem of the felspars not unlike my own, but I inust object to admitting labrr.dorite as a distinct species, o.v as having any higher value than oligoclase, andesine, or the felspars X. and XV. in the present paper. Montreal, Canadft, Mamd 1855. * Poggendorff's Aiinalen, vol. Ixxxix. p. 19, cited in Liebig and Kopp's Jahresbericht, 1853, p. 806.