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THE AMERICAN MINERALOGIST, VOL. 53, MAY-JUNE, 1968 TRICLINIC TALC AND ASSOCIATED AMPHIBOLES FROM GOUVERNEUR MINING DISTRICT, NEW YORK1 MALCOLM Ross, U. S. Geological Survey, Washington, D. C. 20242 WILLIAM L. SMITH, Battelle Memorial Institute, Columbus, Ohio 43203 AND WILLIAM H. ASHTON, Johnson and Johnson, New Brunswick, New Jersey 08903. ABSTRACT New chemical, optical, and X-ray data are given for talc, tremolite, and a manganoan amphibole (tirodite) from the Gouverneur mining district, New York. All talc examined is found to be triclinic, a=5 .255, b=9.137, c=9.44. A, a=90046', P=9855', 1'=90"0', space group C1 or CT, structure type 1-layer triclinic (lTc) . Chemical analysis gives the composition of talc from the Arnold pit as Mg. 04Si, 960JoFo.1O(OH) 1.90. On the basis of fluorine analyses of 22 talcs from worldwide localities it is observed that talc derived from metamorphosed sedimentary rocks contains appreciable fluorine, from 0.11 to 0.48 weight percent, whereas talc derived from ultramafic rocks contains less fluorine. Two of the three tremolite specimens examined have prominent lamellae, oriented parallel to (lOT), of a second amphibole having the following unit-cell parameters: mono- clinic, a=9.50, b=18.04, c=5.28 A, p=1022S', space group P21 or P21/m. Chemical and X-ray evidence indicates that this amphibole is tirodite having the approximate composition Cao.2Mno.Mgs.9Si.022(OH,F)2. The tirodite probably exsolved from the host tremolite at temperatures below 500C. New unit-cell data are given from three tremolites. X-ray powder data are given for talc and tremolite. INTRODUCTION The purpose of this paper is to present new chemical, X-ray, and optical data for talc and the associated amphiboles tremolite and tirodite found in certain schists from the Gouverneur mining district, New York. This study is part of a broader investigation which the authors are conducting on the physical and chemical properties of talc and the associated minerals lying in the system CaO-MgO-Si02-H20-C02 The metamorphosed sedimentary rocks of the New York Grenville Lowlands are ideal for such a study for many of the mineral compositions lie mostly within this system. The present paper will present data only for the taIc-tremolite schists of the Gouverneur area. Although the chemical and physical properties of talc and tremolite were thought to be well known, our study and the recent studies of Bown (1966) and Rayner and Brown (1966) show that much is yet to be done in order to fully characterize these phases. 1 Studies of silicate minerals (10). Publication authorized hy the Director, U. S. Geological Survey. 751 CAM-109 752 MALCOLM ROSS, WILLIAM L. SMITH AND WILLIAM H. ASHTON THE GOUVERNEUR MINING DISTRICT The Gouverneur, or Balmat-Edwards, mining district is in the Grenville Lowlands of the northwest Adirondacks, St. Lawrence County, New York. Most of the bedrock of the Gouverneur area consists of metasedimentary and metasomatic rocks referred to as the Precambrian Grenville Series. The talc containing schists are found in a northeast trending belt which was described by Engel (1962) as more than six miles long, dipping approximately 45 to the northwest probably extending down dip some 2,500 feet, and attaining a maximum thickness of greater than 400 feet. The talc bodies occur as sheets and lenses in a highly folded and sheared marble of the Grenville Series. Metamorphic reactions between quartzite and dolomite produced various magnesium- and calcium-bearing silicates, especially diopside, tremolite, anthophyllite, and talc. Some of the talc and anthophyllite and probably all the serpen tine formed by later alteration of tremolite. Some of the schists are calcitic, probably as a by-product in the alteration of tremolite to a more magnesium rich phase. The amounts of the various minerals differ throughout the area; however, the predominant mineral is usually tremolite. In addition to the pyroxene, amphibole, talc, and serpentine constituents of the ores, there are also varying amounts of quartz, carbonates, gypsum, chlorite, and accessory minerals. Texturally the talcs range from massive to platy, and they vary in color from buff and gray to white. OC:;CURRENCE The Arnold pit of the International Talc Company, near Fowler, was visited in 1961 and again in October, 1966. Many of the samples described in this study were obtained from this pit. The exposed rock at the Arnold pit, near the old Arnold shaft, consisted of a glaciated surface which was being cleared of soil, and into which excavations were being made. The width of the exposure was estimated to be from about 280 to over 300 feet in the area sampled. The sequence of rock types from the footwall dolomite to the hanging wall dolomite was observed to be as follows, as traversed across the floor of the mine in a westerly to northwesterly direction: (1) footwall dolomite (2) "limy talc" rock, about 30 feet (G-16) (3) "coarsely crystalline talc" lens, about 5 feet (G-17) (4) massive "talc ore," about 115 feet (G-18) (5) a sequence of an irregular interbedding of coarsely crystalline TRICLINIC TALC FROM GOUVERNEUR 753 tremolite (variety hexagonite) and massive talc ore, about 130 to 150 feet (G-19, 20, 21, 22) (6) hanging wall dolomite. The occurrence of a lens of coarsely crystalline talc near the footwall was atypical of the exposed rock. The complex interbedding of coarsely crystalline talc and the hexagonite-bearing rock was pronounced toward the hanging wall. The exposures of this type of talc ranged from a few inches to a few feet in width. The specimens of the coarsely crystalline talc which were collected for mineralogical study were found to be dominantly talc with a small amount of clear unaltered tremolite. The relatively coarse grained talc, known as "scale" at the mines, is associated with but distinctly different from the tine-grained commercial talc. A similar coarsely crystalline talc was noted in May, 1961, on the fourth level of the Wight mine of the International Talc Company, which is located about 3,000 feet to the southwest of the Arnold pit, in the same formation. The material from this part of the mine is richel in tremolite; the translucent to pure white talc and clear colorless tremolite being the major phases. Minor fibrous anthophy llite, partly altered to talc, is also present as a minor constituent. The sheetlike body of tremolite-coarsely Wi . . . FIG. 1. Index map of the Gouverneur talc mining areas, St. Lawrence County, New York. Modified, in part, from Engel, 1962, Plate 1. 754 MALCOLM ROSS, WILLIAM L. SMITH AND WILLIAM H. ASHTON crystalline talc rock was about 12 feet thick where examined and was reported to extend more or less continuously along the strike of the ore. The body extends from the surface or near the surface down through the sixth level of the mine. Additional samples of well crystallized talc obtained previously from the Arnold pit (G-1), and the "Talc" mine (CS-1), Gouverneur, N.Y., and also a sample of nearly pure quartz-tremolite rock from an area 3/4 of a mile southwest of the Wight mine (G-24) were also studied. The location of the various mines is given in the index map (Figure 1). The apparent mineral associations of the more carefully studied samples are as follows: (1) G-1, talc-minor clear tremolite and anthophyllite (2) G-16, clear tremolite-serpentine-talc-minor carbonate and tirodite (3) G-17, talc-minor clear tremolite (4) G-19, 21, lavender tremolite (hexagonite)-minor quartz, carbonate, tirodite, and tourmaline (5) G-24, tremolite-quartz-minor tirodite Small amounts of carbonate appear as a cementing agent in samples G-16 and G-21. On the basis of a rapid reaction to dilute HCI the cementing carbonate is probably calcite. TALC Chemical composition.-The coarsely crystalline talcs (G-1, G-17) taken from the Arnold pit in 1961 and 1966 are nearly pure, only a few small crystals of tremolite appear on careful optical examination of the picked material. Three spectrographic analyses (Table 1) show less than 0.2 percent calcium thus the amount of included tremolite is negligible. Wet chemical analysis (Table 2) confirms the presence of fluorine in the talc structure. Total loss (H20+ F) on ignition for samples G-1 and G-17 are given in Table 3. The chemical formula of this talc as given by the analysis G-1 is: Mga.04Sia.960looF .lo(OH) 1.90 The analysis shows a few tenths of a percent excess H 20 and this is considered due to analytical error. The small amounts of Fe, Mn, AI, Ca, etc., shown to be present are assumed to be mainly due to the small amount of tremolite. Partial chemical analysis for H 20 and fluorine were also made of talc (G-17) and tremolite (G-21) sampled from the Arnold pit in 1966 (Tables 1 and 3). Fluorine analysesl for a number of other talc specimens obtained 1 The samples were fused in 3.5 grs. of sodium carbonate, cooled and leached out in weak sulfuric acid. Samples were then transferred to stills and 100-125 m!. of 1:2 H2SO. TRICLINIC TALC FROM GOUVERNEUR 755 TABLE 1. SPECTROGRAPHIC ANALYSES OF TALC AND TREMOLITE FROM THE GoUVERNEUR TALC DISTRICT, NEW YORK Talc (G-l)' Talc (G-l)b Talc (G-17)c Tremolite (G-21)d Tremolite (G~24)f Si >10% 20--40 20--40 20-40 Mg >10 20--40 20--40 15-30 Fe 0.03 0.1 0.1 0 .2 Mn 0.03 0.01 <0.005 0.3 Al 0.03 0.1 0.05 0.2 Ti 0.001 0.01 0.005 0.02 Ni _e <0.005 <0.005 <0.005 Cu <0.005 <0.005 <0.005 Li 0.001 0.005 0.005 0.02 Na 0.01 0.05 0.05 0 .5 K 0.001 0.01 0.02 0.1 Ca 0.03 0.2 0.1 5-15 Sr <0.005 Ba <0.005 F 1.0 0 .30' 20--40 10--20 0.1 1-2 0.3-1.0 0.03 0.1-{).3 0.1-{).3 5-15 0.31g Arnold pit, Analyst: C. L. Waring, U. S. Geological Survey. b Arnold pit, Analyst: Ber~ard Snyder, Battelle Memorial Institute. Arnold pit, Analyst: Bernard Snyder. d Arnold pit, lavender tremolite, Analyst: Bernard Snyder. C - not looked for. f Colorless tremolite, 3/4 mile SW of Wight mine, Balmat, N. Y., Analyst: Bernard Snyder. " By wet chemical analysis. from worldwide localities were made to obtain more knowledge on the range of fluorine content in this mineral. These fluorine analyses are given in Table 4. Physical properties.-Talc specimens collected from the Arnold pit show two distinct habits; one variety is fine grained somewhat fibrous in nature (G-16) and is associated with white tremolite. The second variety is coarsely crystalline (G-1, 17), often occurring in nearly mono-minerallic zones. Only the coarse variety was studied by X-ray techniques. The coarsely crystalline talc forms platy crystals up to 1 cm in width. The crystals are pure white, translucent, with a slight adamantine luster. Some crystals grow as nearly perfect pseudotrigonal pyramids lying on (001). Often the pyramids are truncated by a small (001) face. added (volume kept below 150 mi.). Fluoride was separated from interfering substances according to the method of Willard and Winter (stearn distillation at 165C). The distillate was collected in 500 m!. volumetric flasks. Fluoride content of the distillate was then determined by a thorium nitrate colorimetric titration. 756 MALCOLM ROSS, WILLIAM L. SMITH AND WILLIAM H. ASHTON TABLE 2. CHEMICAL ANALYSES OF TALC (G-1) FROM ARNOLD PIT, FOWLER, N. Y. G-1' Ratiosb Ideale SiO, MgO F H 20 (-) H,O(+) 62.68 32 .33 0.48 0 .33 4 . 79 3 .958 3 .042 0.096 1 . 009 63.37 31.88 4.75 100.00 Total O=F/ 2 100.61 -0.20 100.41 Arnold pit, collected in 1961, Analysts: Joan Lathouse and R. D. Foltz, Battelle Memorial Institute. b Ratios calculated on basis of Mg+Si = 7 .000. e Mg3Si,O\O(OH).. Ten talc crystals from sample G-l were examined with the Buerger precession camera. All crystals gave identical unit-cell parameters; the best measurements are given in Table S. This talc is triclinic; the space group is cI or C1, and the structure type is one-layer triclinic C1Tc). In contrast to photographs of the common micas, the Okl and hkO precession precession photographs show a strong triclinic intensity distribution. There is little apparent monoclinic pseudosymmetry in any ot the X-ray photographs. X-ray powder data for this material are given in Table 6. Two talc crystals from sample G-17, one crystal from a sample from the "Talc" mine, Gouverneur, N. Y. (CS-l) and one crystal from a Balsam, North Carolina, sample (CS-2) were also studied by precession TABLE 3. FLUORINE AND H 20 ANALYSES FOR TALC AND TREMOLITE' Total loss (H2O+F) in weight percent Talc (G-1) Obs. Calc. Talc (G-17) Obs. Calc. Tremolite (G-21) Ous. Calc. to 110 110- 550 550- 1000 F H20 (+) 0 .33 0.57} 4 . 70 0.48 4 . 79 0.0 4.99 0.48 4.51 0.12 0.19} 4.33 0.42 4.10 0.0 4.96 0.12 4.54 0 .05 0.11} 1.45 0.30 1.26 0.0 2.37 0.30 2.07 Analyst: Joan Lathouse, Battelle Memorial Institute. TRICLINIC TALC FROM GOUVERNEUR 757 TABLE 4. FLUORINE ANALYSES OF TALC FROM VARIOUS LOCATIONS AND ORIGINS Sample Location and Origin %F G-l G-17 WA-3 42771 E 23 25 30 26 11 S 423 7 8 31 29 32 28 14 33 WA-lb 3 27 13 Gouverneur talc district, New York 0.48 Gouverneur talc district, New York .42 Gouverneur talc district, New York, .45 metamorphosed magnesian carbonate sediments. Val Chisone, Italy .44 Val Chisone, Italy .31 metamorphosed magnesian carbonate sediments. Murphy, North Carolina, .36 metasomatic replacement of magnesian carbonate sediments. Inyo County, California, .34 replacement of quartzite along dolomite contact. Brumado, Bahia, Brazil, .29 magnesia metasomatism of siliceous carbonate sediments. Casa Nova, Bahia, Brazil, . 27 lenses of replaced siliceous magnesian carbonate sediments. Windsor County, Vermont, .26 schistose talc-carbonate rock, not of ultrabasic origin, but asso- ciated with ultrabasic body. Allamoore, Texas, .20 metamorphism of interbedded limestone and magnesia rich tuff. Madoc, Ontario, Canada, .18 metamorphosed magnesian carbonate sediments. Dillon, Montana, .18 replacement of dolomite in fracture zones. Flinders Range, South Australia, .17 metasomatism of silicified magnesian carbonate sediments. Esmeralda County, Nevada, . 17 metamorphosed quartzite lens in dolomite. Tong yang, South Korea, .16 metamorphosed magnesian carbonate sediments. Dausa, Rajasthan, India, .11 metamorphosed magnesian carbonate sediments. Tamaulipas, Mexico, .04 hydrothermally altered basic dike, enclosed in serpentinized schist. Lamoille County, Vermont, .04 automorphic alteration of ultrabasic rock, associated with serpentine. Zambales, Philippines, .01 altered ultrabasic rock, associated with serpentine. Transvaal, South Africa, .007 altered ultrabasic rock, associated with serpentine. Providence County, Rhode Island, .004 associated with serpentine pods in greenstone. Note: Sediments refers to metamorphic rocks of sedimentary origin. 758 MALCOLM ROSS, WILLIAM L. SMITH AND WILLIAM H. ASHTON TABLE 5. UNIT-CELL DATA FOR TALC Arnold pit, G-l ca pb a (A) b (A) c (A) fj "Y 5 . 27, 9 . 137 9.44, 9046' 9855 ' 900' 5.27, 5.27. 9.45. 8453' 9859' 1200' System triclinic Diffraction symbol Ic. triclinic Ip. Structure type ITc ITc AB CD E pb 5 . 29 5.30 9 . 47 866' 9854' 1200' 5 . 26 9 . 10 18.81 1000' 5 . 27 9 . 13 18.88 10015' 5.27 9 . 13 18.94 100'40' 5.287 9.15. 18 .95 99JO' triclinic monoclinic monoclinic monoclinic monoclinic Ip. C. l e C. l e ITt 2M, 2M, 2M, 2M, C-setting (preferred setting). b P-setting (conventional setting) A Rayner and Brown (1966), Harford County, Md. B Gruner (1934), Harford County, Md. C Hendricks (1938), Harford County, Md. D Zvyagin and Pinsker (1949). E Stemple and Brindley (1960). Manchuria. techniques. All give the same unit-cell data as that given III Table S. Ross, Takeda, and Wones (1966) have shown that many mica samples are composed of more than one polytype. Thus a number of crystals from a given layer silicate sample should be examined before assuming the specimen is homogeneous. Talc G-1 from the Arnold pit appears to be so. Our present study coupled with that of Rayner and Brown (1966) suggests that most talc is triclinic. Previous reports of the monoclinic form may be in error. Unit-cell data for tales studied previously are compared to that of the Arnold pit tale in Table S. X-ray data for sample G-1 is given both in the C-centered setting and in a conventional primitive cell setting so that it may be compared to the results of Rayner and Brown. The transformation matrix from the C-centered unit-cell to the conventional primitive cell is: 1001 -1/2 -1/2 01001. The C-centered setting is preferred for it facilitates comparison with other layer silicate structures. Rayner and Brown examined the same specimen as that studied by Hendricks in 1938 and probably is also identical to that examined by Gruner in 1934. Thus, the only evidence for a two-layer monoclinic tale is the work of Stemple and Brindley (1960) and Zvyagin and Pinsker (1949). The optical properties of the Arnold pit tale (G-l) are: biaxial positive, optic angle variable ranging from 00 to 10, a=l.S4S0.002, /3='Y= l.S84O.002. The value of the optic angle is highly dependent on the TRICLINIC TALC FROM GOUVERNEUR 759 TABLE 6. OBSERVED" AND CALCULATEDb X-RAY POWDER DATA FOR TALC (G-1) FROM THE ARNOLD PIT. GOUVERNEUR. N. Y., MINING DISTRICT C-setting hkl P -setting hkl d (calc.) A d (obs.) A Ie 001 001 9.333 9.34 vs 002 002 4.667 4.68 w 020 010 4.568 4.56 s IlO 100 4.531 110 IlO 4.523 TIl 111 4.316 III T01 4.298 021 011 4.14 vw ''''I021 OIl 4.082 lI1 101 3 . - 3.85 vW 111 III 3.862 1I2 Il2 3 .504 3.43 w Il2 102 3.481 022 012 3.287 022 012 3.243 003 003 3.111 3.115 s lI2 102 3.061 112 112 3.040 II3 Il3 2.751 Il3 103 2.733 130 110 2.632 130 120 2.627 2.632 wOO 201 211 2.617 200 210 2.606l 2.598 m 131 121 2. 590f 023 013 2.588 131 TIl 2.578 023 013 2.555 131 111 2.490} 2.48 sd 131 121 2.472 202 212 2.442 1I3 103 2.424 201 2Il 2.415 113 113 2.4D9 132 122 2.382 132 TI2 2.361 004 004 2.333 2.336 V\V " CuKa radiation, Ni filter (}o.= 1.5418 A). Camera diameter: 114.59 mm. Lower limit 28 measurable: approximately 8 (11.0 A). b Calculated from the following unit-cell parameters: a=5.275, b=9.l37, c=9.448 A, a =9046', tJ=9855', "),=900', space group CT. All calculated spacings are given to d=2.284 A. vs (very strong), s (strong), ms (medium strong), m( medium), wm (weak medium), w (weak), vw (very weak), d (diffuse). 760 MALCOLM ROSS, WILLIAM L. SMITH AND WILLIAM H. ASHTON C-setting Izkl 040 TABLE 6. (Continued) P-setting hkl d (calc.) A d (obs.) A ()20 2.284 2.284 2.219 2.103 1.994 1. 871 1. 731 1.688 1.558 1.527 1.515 1.320 1.296 1 .271 /- vw m-d m-d wm m w vw-d w ms w w w vw amount of twinning in the crystal; highly twinned crystals have low optic angles. AMPHIBOLES Chemical properties.- Two varieties of tremolite occur in the Arnold pit specimens; one lavender to pink in color (G-19, 21), the other pure white (G-16, 17). The lavender form occurs in large prismatic crystals several millimeters long. The varietal name "hexagonite" is often used to describe this tremolite; the type material reported as coming from Edwards, St. Lawrence County, N. Y. (Dana, 1892, p. 389, 393). The white variety of tremolite is associated with the "limy talc" (G-16) and to a small extent, with the coarsely crystalline talcs (G-1, 17). The lavender tremolite occurs in nearly mono-mineralic zones between the massive talc ore and hanging wall dolomite. An exceptionally well-crystallized colorless tremolite rock collected 3/ 4 of a mile southwest of the Wight mine was also examined (G-24). Spectrographic analyses of the lavender and colorless varieties (G-21, G-24) are given in Table 1. Quantitative analyses for H 20 and fluorine for the G-21 tremolite are given in Table 3. The analyzed samples G-21 and G-24 contain a small amount of tirodite and quartz. Engel (1962, p. 309) gives complete mineral analyses for two tremolites collected from the old Arnold mine. These analyses are recalculated in our Table 7. The various analyses (Table 1, 7) show that the Gouverneur tremolites have a nearly end-member composition with some MnH , K, and Na replacing calcium, F replacing (OH), and Al replacing Si. There are four different occupied cation sites in the tremolite crystal TRICLINIC TALC FROM GOUVERNEUR 761 TABLE 7. TREMOLITE CHEMICAL ANALYSES FROM ENGEL (1962, p. 309) Weight percent Atomic ratios" Q' 15b 9b 15 SiO, A],O, F e, Oa MgO FeO TiO, MnO CaO K ,O Na20 H 2OH 2O+ F CI CO 2 57.83 0 . 57 0.20 24 .25 0.11 0.03 2.81 11.42 0.14 0 . 17 0.06 2 .09 0.41 0.01 0.00 100 . 10 57.76 0.64 0 .00 24.73 0 . 14 0 .05 0.06 13 . 27 0.09 0 . 28 0 . 13 2.38 0 .26 0.02 99.81 Si 7 .915 7.897} 8.00 1 Al 0 .092 8.028 0 . 10-1, FeaJ. 0 .021 Mg 1.9-1-5 5 . 038 FeH 0.012 5 .285 0.016 5 .066 Ti 0 .003 0 . 005 MnH 0 . 325 Ca 1.675} 0 .007 1.944 K 0.025 1.744 0 .016 2 .033 oNa .().!4J O. 0 73J OH 1.907 (1 .820) 2.170 (1. 882) F 0 . 178} 0 . 180 0.113} 0.118 CI 0 .002 0.005 O=F+CI 0.17 0.11 99.93 99.70 Arnold No.3 mine, 11th level, F owler, N. Y. b Arnold mine, 14th level, Fowler, N. Y. Number of ions on the basis of: number of oxygen atoms=22.00 and (OH)=2.00F-Cl. structure, designated M I , M 2, M s, and M 4 The smaller metal atoms such as Mg and Fe enter the M I , M 2, and Ms sites whereas the larger cations such as Ca and Na enter the large M4 site. With our present knowledge of amphibole structure we do not expect any alkalies or alkaline earths to enter the M I , M 2, or Ma sites. Ideally the M4 site should take up 2.00 calcium atoms per formula unit. The small cations, however may enter the M4 sites in appreciable quantities replacing some of the calcium or sodium. Physical properties.- X-ray studies of the lavender and white tremolite were made using both single crystal and X-ray powder techniques. The lavender tremolite specimens (G-19, 21) are essentially mono-mineralic. The crystals appear optically perfect with no evidence of twinning, exsolution or alteration. Single crystal photographs show tremolite G-21 to be monoclinic, space group C2/ m, Cm, or C2 with a = 9.816 A, b = 18.04, 762 MALCOLM ROSS, WILLIAM L. SMITH AND WILLIAM H. ASHTON TABLE 8. UNIT- CELL DATA FOR TREMOLITES FROM THE GOUVERNEUR, NEW YORK TALC DISTRICT G-21" G-24" G-16d Single crystal Powderb Single crystal Powderb Single crystal a (A) b (A) c (A) (j V (A3) 9.81. 18.04 5.27. 10430' 904.4 9.818 (5) 18.047 (8) 5.275(3) 10439' (3') 904.2(6) 9.79. 18.04 5.28, 10425' 903.9 9.812 (2) 18 .077 (3) 5 . 273 (2) 10443' (2') 904 . 5 (3) 9.81s 18.04 5.281 10435' 904.2 System monoclinic monoclinic monoclinic Diffraction symbol C*/* C*/' C'/' Lavender tremolite, Arnold pit, St. Lawrence County, N . Y. b Obtained from least-squares refinement of powder data given in Table 9. Errors in thousandths of an Angstrom and minutes given in parentheses. " White tremolite, 3/ 4 mile SW Wight mine, N. Y. d White tremolite, Arnold pit, St. Lawrence County, N. Y. c = S.276, and {3 = 10430'. The hOI precession photographs exposed to unfiltered molybdenum radiation for 100 hours show extremely weak spots representing a second phase. X-ray data for this tremolite are summarized in Table 8. X-ray powder data for tremolite G-24 and G-21 are given in Table 9. Spectrographic analysis was given in Table 1. In addition to lavender tremolite described above two white tremolites (G-16, G-24) were examined by X-ray single crystal techniques. Both tremolites show, under crossed nicols, thin lamellae oriented parallel to the (101) plane. In sample G-24 the lamellae are so distinct they can be seen in the hand specimen with a low power binocular microscope. Precession photographs of both specimens give unit-cell data elose to that of the lavender tremolite (Table 8). Superimposed on the strong single-crystal patterns of the host tremolite phase is a weaker pattern of a second amphibole. This second phase is a elino-amphibole having space group symmetry P2dm or P2 1 with a=9.48 A, b= 18.03, c=S.29, and {3= 101SS'. The unit-cell data for the P2dm amphiboles (G-16 and G-24) are given in Table 10 where the data is compared to that obtained by Bown (1966) on a similar specimen. As pointed out by Bown, who first reported existence of this P2dm amphibole, the two coexisting amphibole phases have a common b-axis with the b-dimensions almost identical. The TRICLINIC TALC FROM GOUVERNEUR 763 TABLE 9. OBSERVED" AND CALCULATEDb X-RAY POWDER DATA FOR WHITE (G-24) AND LAVENDER (G-21) TREMOLITE FROM THE GOUVERNEUR, N. Y. MINING DISTRICT Tremolite, G-24 hkl d (calc.) A d (obs) A [ Tremolite, G-21 d (calc.) Ad d (obs) A / 020 9.039 9.054 15 9.024 110 8.403 8.410 40 8.405 001 5.100 5.092 20 5.103 130 5.087 5 .082 5.046 60 III 4.873 4.875 10 4.873 4.866 5 200 4.745 4.751 10 4.749 4.739 10 040 4 . 519 4.523 30 4.512 4.514 10 021 4.441 4.442 220 4.201 4.209 15 4.203 4.197 50 201 4.020 4.028 5B 4.021 111 3.980 nn 3.875 3.880 15 3.984 3.873 3.878 10 221 3.673 3.673 041 3.382 131 3 . 379 3.380) 3.380 3.373 25 150 3.379 3.374 240 3.273 3.272 65 3.271 3.274 85 310 3.116 3.120 100+ 3.119 3.115 100+ 201 3.103 3.107 311 3.016 3.016 3.013 5 060 3.013 3.008 241 3.004 3.004 5 3.002 151 2.942 2.944 45 2.939) 2.942 35 221 2.935 2.937 330 2.801 2.802 25 2.802 331 2.727 2.727 2.727 20 151 2.706 2.712 100+ 2.705 2.709 60 Il2 2.608 2.609 061 2.594 2.594 35 2.591 2.589 15 241 2.558 2.557 5 2.559 CuK", radiation, Ni filter (X = 1.5418 A). Pattern taken with North American Philips X-ray diffractometer internally standardized with sodium fluoride. Specimens contain a small amount of quartz and tirodite. b All calculated interplanar spacings are given down to d = 2.530 A. Calculated spacings less than this are given only where indexable to an observed spacing. Calculated from the following unit-cell parameters: a=9.812 A, b= 18.077, c=5.273, i3=10443', space group C2/m. Composition by electron microprobe anal- ysis: Ca\.SMno.aMgs.2Siso...(OH, F),. d Calculated from the following unit-cell parameters: a=9.818 A, b= 18.047, c= 5.275, i3 = 10439', space group C2/m. 764 MALCOLM ROSS, WILLIAM L. SMITH AND WILLIAM H. ASHTON ilkl 002 260 202 350 351 420 312 242 171 132 261 152 202 280 351 370 190 422 510 460 442 530 441 172 223 372 282 133 '2, 10, 1 461 1,11,0 403 600 TABLE 9. (Continued) Tremolite, G-24 d (calc.) A, d (obs) A Tremolite, G-21 d (calc.) Ad d (obs) A ! 2.550 2.543 2.530 2.381 2.335 2.295 2 . 272 2.208 2.182 2 . 1641 2.162J 2.130 2.0401 2.040J 2.015 2.000 1.965 1.962 1.888 1.864 1.837 1.810 1.805 1.726 1. 716 1. 713 1.685 1.683 1.649) 1.648 1.619 1.586 1.582 2 . 530 2 .379 2 .295 2. 267 2.182 2.164 2. 132 2 . 046 2.015 1.999 1.961 1.887 1.864 1 .805 1. 710 1.685 1. 675 1.649 1.617 25 15 20 20 5 55 5 10 25 10 10 30 15 10 5 15 10 40 15 2 . 552 2.541 2.530 2.380 2.334 2. 296 2.272 2.207 2 . 180 2.166 2. 161 2. 129 2.043 2.038 2.015 1.999 1.9621 1. 962J 1.889 1 .864 1.836 1 .812 1.806 1.725) 1. 716 1. 712 1.684) 1.683 1.646) 1. 648J 1.617 1.5861 1. 583) 2.531 2.379 2.336 2 .295 2.268 2 .210 2.177 20 100+ 45 20 20 5 10 2.161 2.043 25 5 2 .015 1 . 998 1.961 1.892 1.864 1.836 1.810 30 100+ 15 35 10 10 15 1. 720 15 1.685 10 1.648 1.618 1.585 1.561 30 30 20 5 (Table 9 continued on following page) IIkl 571 402 1, 11, 1 282 '263 482 2,10,2 0, 12, 1 591 731 TRICLINIC TALC FROM GOUVERNEUR i65 TABLE 9. (Continued) Tremolite, G-24 d (calc.) A, d (obs) A Tremolite, G-21 d (calc.) Ad d (obs) A I 1.555 1. 551 1.524 1.514 1.512 1.502 1.471 1.445 1.398 1.365 1. 555 10 1.525 1.511 1. 503 1.470 1.445 1.433 1.398 1 . 365 10 10 20 10 10 35 10 15 1. 555) 1. 553J 1.522 1. 514 1.511 1. 501 1. 469 1.443 1 . 554 1.530 1.514 20 10 100+ 1.468 1.435 5 75 a-axes of the tremolite and P2 d m amphibole lie in a common (010) plane and at an angle of 230' of one another. The study by Bown was made on a tremolite from the Wight mine, St. Lawrence County, N. Y. showing "extremely fine (001) lamellae." His material is probably very similar in composition to specimens G-16 and G-24. In the 121m setting of Bown TABLE 10. UNIT-CELL DATA FOR THE SECOND AMPHIBOLE PHASE EXSOLVED FROM THE GOUVERNEUR TREMOLITES G-24a G-16b MgBown (1966)- cummingtonited a (A) b (A) c (A) {3 V (A') System Diffraction symbol 9.502 18.04 5.284 10225' 884.6 monoclinic P2!/* 9.476 18.03 5 . 28, 10155' 883.5 monoclinic P2 1/ . 9.51 17.95 5.27 1020' 880.0 monoclinic P2!/. 9.467 17 .937 5.292 10214' 878.1 monoclinic C.I.? Data obtained from the same single crystal patterns as those of tremolite G-24 (Table 8). b Data obtained from the same single crystal patterns as those of tremolite G-16 (Table 8). - Cell edges transformed from the I-centered cell: a=9 .87 A, b=17.95, c=5.27, {3 = 109.5, space group 121m. d Unit-cell data of an iron free cummingtonite, Mg,SisO,,(OHh, as extrapolated by Viswanathan and Ghose (1965). 766 MALCOLM ROSS, WILLIAM L. SMITH AND WILLIAM H. ASHTON the lamellae are oriented parallel to the (00l) plane. Bown suggested that the lamellae are clino-anthophyBite. Ross, Papike and Weiblen (1968) have made a more complete study of the composition and structural state of the amphiboles in sample G-24 and also have studied a sample of the manganoan amphibole tirodite (Segeler, 1961) from the International Talc mine No.3 in the nearby Talcville, N. Y. area. X-ray precession photos and least-squares powder refinement of tirodite give the following unit-cell data: a=9.550 0.001 A, b=18.0070.003, c=5.2980.001, ~=10239'l', space group P2 1/ m or P2 1. The single crystal photos also show a weaker pattern of a second amphibole oriented parallel to the (101) plane of tirodite. The unit-cell data for this second phase is: a=9.78 A, b= 17.99, c=5.27, ~= 10425', space group C2/m. The (101) lamellae can be seen optically in the tirodite grains. Electron microprobe scans over the Talcville tirodite give the approximate composition as Cao.4Mn1.2Mg5.4Si8022(OH,Fh The lamellae are about one micron thick and have a much highel calcium and lower manganese content than the host tirodite phase. Microprobe examination of sample G-24 shows that in addition to the crystals of calcium-rich tremolite there are a few grains of a manganeserich amphibole. The lamellae in the tremolite are manganese-rich and similar in composition to tirodite. The lamellae in the Mn-rich amphibole are calcium-rich. The approximate compositions of the tremolite and Mn-rich host phases are Ca1.6Mno.aMg5.2Si8022(OH, Fh and CaQ.2Mno.9Mg6.9Si8022(OH, F)2 respectively. Chemical and X-ray evidence leaves no doubt that sample G-24 contains two amphiboles, tremolite and tirodi~e, with tremolite exsolving tirodite and tirodite exsolving tremolite. It is estimated that tirodite composes about 5 weight percent of the sample. The tirodite sample from Talcville is an analogue to sample G-24, the major phase is tirodite, the minor exsolved phase is tremolite. In order to obtain more precise unit-cell data for the lavender and white tremolites (G-21 and G-24) the X-ray powder diffractometer data (Table 9) was subjected to least-squares refinement. The refined parameters are compared to the single crystal X-ray data in Table 8. The amount of tirodite in sample G-21 is probably less than one weight percent and in sample G-24, probably less than 5 weight percent. No lines of tirodite could be detected in either sample and thus should not have effected the refinement. The optical properties of all three tremolites studied (G-16, G-21 and G-24) are nearly identical (biaxial negative, a = 1.604 0.002, ~ = 1.612 0.002 and 'Y = 1.628 0.002), suggesting similar chemical compositions. The lavender variety does not show (101) lamellae although the X-ray TRICLINIC TALC FROM GOUVERNEUR 767 photographs show definitely that the second amphibole phase is present but composing probably less than one volume percent of the crystal. The lamellae are much more pronounced in G-16 and G-24 and the X-ray diffraction single crystal patterns of the lamellae are relatively strong with many reflections appearing in the hOI, hll, and h21 nets. DISCUSSION Talc.~Talc deposits may form by the metamorphism of carbonate rocks, by the replacement of silicified carbonate rocks, or by the alteration of ultramafic rocks. There are reported occurrences of talc formed from mafic and felsic igneous rocks, pegmatites, tuff, and low magnesian sediments; however, these involve complex and unique conditions that are atypical of the major occurrences. Talc bodies may also form by contact metamorphism in rare instances where the chemical conditions are correct. Twenty-two specimens of essentially pure talc obtained from nineteen different deposits have been analyzed for fluorine content (Table 4). All of the talc samples were found to contain fluorine. Although too few samples have been studied to permit firm conclusions to be drawn, the following relationships may be inferred: (a) Talc from deposits believed to be derived from the metamorphism of carbonate sedimentary rocks, formed by the replacement of silicified carbonate rocks, or occurring in talc-carbonate-amphibole schists, were found to contain 0.11 to 0.48 percent fluorine. (b) Talc from the five deposits believed to be derived from the alteration of mafic or ultramafic rock, and which are intimately associated with serpentine, show fluorine content below 0.04 percent. The present study coupled with that of Rayner and Brown (1966) definitely shows that the common variety of talc has a one-layer triclinic structure. Other polytypes, if they occur will probably be rare compared to the 1Tc form. To summarize, talcs from the following localities have been shown to have the one-layer triclinic structure: (1) Harford County, Maryland, U.S.N.M. 82519 (2) Arnold pit, St. Lawrence County, New York (3) "Talc" mine, St. Lawrence County, New York (4) Balsam, North Carolina. Tremolite.~Engel and Engel (1968) suggest that the temperature of metamorphism in the Gouverneur mining district in the is 500 to 600C range. Some of the tremolites were enriched in manganese at the expense of calcium and sodium (e.g., Table 7, analysis 9b). The evidence given by Ross, Papike and Weiblen (1968) shows that the manganese-enriched 768 MALCOLM ROSS, WILLIAM L. SMITII AND WILLIAM II. ASIITON tremolite coexisted with a second amphibole tirodite which was enriched in calcium. On cooling both phases unmixed to produce the (101) lamellae. Apparently at high temperatures the M4 site can hold appreciable quantities of manganese. The appearance of exsolution lamellae in tremolite should be very useful in understanding the paragenesis of the Gouverneur schists and can also give information on the extent of solidsolution in tremolites. Alteration oj the tremolile-bearing schists.-Optical and X-ray examination of a number of tremolite rocks from the Gouverneur area show the following retrograde alteration sequences: (1) Sample CS-1, "Talc" mine tremolite+ talc........an thophyllite+ talc (2) Sample G-2, International talc mine, N. Y.; G-5, Fullerville, N. Y. tremolit e........anthoph yllite........ talc (3) Sample G-6, Fowler, N. Y. a n t h o p h y llite........ t a l c (4) Sample G-18, Aronold pit tremolite........serpen tine (5) Sample G-26, Wight mine tremoli te........anthophyllite........talc? Tremolites CS-1, G-5, and G-26 show prominent exsolution lamellae. Stemple and Brindley (1960) give evidence for the transformation tremolite........talc in a specimen from the Gouverneur area. All of the very fine grained talc, anthophyllite, and serpentine noted in the Gouverneur schists appear to have grown by a latter alteration of tremolite or anthophyllite. The coarsely crystalline talc (e.g., G-1, G-17) is associated with clear unaltered tremolite and appears to be a primary metamorphic assemblage; not a result of any retrograde alteration. The coarsely crystalline talc is not valuable commercially because of its poor milling quality. The fine-grained alteration products of the amphiboles (e.g., G-16, G-18) forms the commercial ore. The superior milling quality of this ore is probably due to the fine-grained nature of the magnesium silicate alteration products. ACKNOWLEDGEMENTS We wish to thank Margaret H. Appleman for preparing the tremolite X-ray powder patterns and handling the computer computations, Paul W. Weiblen of the University of Minnesota for the electron probe analysis, and James J. Papike for advice on amphibole crystal chemistry. REFERENCES BOWN, M. G. (1966) A new amphibole polymorph in intergrowth with tremolite: Clinoanthophyllite: Amer. Mineral ., 51, 259-260. TRICLINIC TALC FROM GOUVERNEUR 769 DANA, E. S. (1892) System of Mineralogy. 6th ed.: John Wiley and Sons, Inc., New York. ENGEL, A. E . J. (1962) The Precambrian geology and talc deposits of the Balmat-Edwards District, northwest Adirondack Mountains, New Yark. U. S. Geol. Surv. Open File Rep., 357p. ENGEL, A. E. J. AND CELESTE G. ENGEL (1958) Pr~gressive metamorphism and granitization of the major paragneiss, northwest Adirondack Mountains, New York. Geol . Soc. Amer. Bull., 69, 1368-1414. GRUNER, J. W. (1934) The crystal structures of talc and pyrophyllite. Z. Kristallogr., 88, 412-419. HENDRICKS, S. B. (1938) On the crystal structure of talc and pyrophyllite. Z. Kristallogr., 99, 264-274. RAYNER, J. H. AND G. BROWN (1966) Triclinic form of talc . Nature, 212, 1352-1353. Ross, M., H. TAKEDA AND D. R. WONES (1966) Mica polytypes: Systematic description and identification. Science, 151, 191-193. Ross, M., J. J. PAPIKE AND PAUL W. WEIBLEN (1968) Exsolution in clinoamphiboles. Science (in press). SEGELER, C. G. (1961) First U. S. occurrence of manganoan cummingtonite, tirodite. Amer. Mineral. 46, 637-641. STEMPLE, I. S. AND G. W. BRINDLEY (1960) A structural study of talc and talc-tremolite relations . J. Amer. Ceram . Soc. 43, 34-42. VISWANATHAN, K. AND S. GHOSE (1965) The effect of MgH - FeH substitutions on the cell dimensions of cummingtonites. Amer. Mineral. 50, 1106-1112. ZVYAGIN, B. B. AND Z. G. PINSKER (1949) Electronographic determination of the elementary cells of pyrophyllite and talc and structural relation of these minerals to montmorillonite. Dokl. A cad. Sci. USSR 68, 505. Manuscript received, July 18, 1967; accepted Jor publication, September 25, 1967.