Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/431

Rh MINERALOGY 413 in very thin plates. Generally uniaxal, sometimes with diver gence ==56. Metallic, pearly. Usually dark green, brown, or black; streak greenish grey or white. B. B. difficultly fusible to a grey or black glass. Completely sol. in concentrated s. acid, leaving white Fig. 488. Fig. 489. pearly plates of silica. C.c. : 39 silica, 17 alumina, 10 iron protoxide, 20 magnesia, 9 potash. Hillswick, Shetland, in gneiss; Sutherland, Ross, Inverness, in limestone; Skyeand Fife in trap; Pargas, Boden- mais, Greenland, New York. JRubcllan is a decomposedTvariety. 513. HAUGHTONITE, (Al.Fe) Si + (Fe, K),Si. Oblique prismatic. Cl. basal, perfect. H. =3; G. 3 1. Vitreous to adamantine. Chocolate-brown to black. Weathers pah- green and ochry. Difficultly soluble in acids. B.B. fused with difficulty to a highly magnetic bead. C.c. : silica 36, alumina 18, ferric oxide 4 5, ferrous oxide 18, magnesia 9, potash 8, water 3. Common in the granites of Scotland. Black Forest, Harzburg, Tyrberger. 514. LEPIDOMELANE, (Al,Fe) Si + (Fe, K)Si. Oblique prismatic. Cl. basal, perfect ; brittle. H. =3; G. =2 97. Vitreous; transparent to opaque. Rich brown to raven-black. B. B. fuses easily to a black feebly-magnetic bead. Sol. in h. acid, leaving pearly scales of silica. C.c.: 37 silica, 17 alumina, 24 iron peroxide, 3 protoxide, of iron, 8 potash, 10 magnesia, 4 water. Rarely in gneiss, Scotland; common in granite, Ireland; and Pers- berg, Sweden. 515. ANOMITE, 12Mg, 3A-1, 2K, if, 12Si, Oblique prismatic, c :m 98 42. Form c, m, o, b (see fig. 488); divergence of optic axes 12 to 16. Monroe(New York), Lake Baikal. 516. PHLOGOPITE, (f R 3 + JR) Si 3. Oblique prismatic. OP (c), P (m), - JP (o), oopoo (b). c : m 98 30 to 99. Cl. basal, perfect. H. =2 5 to 3; G. =275 to 2 97. Pearly to submetallic. Yellowish brown with copper-like reflexion; also green, white, and colourless. Transparent. Divergence of optic axes 3 to 20. C.c.: 14 alumina, 2 protoxide of iron, 28 mag nesia, 8 6 potash, 2 &quot;57 fluorine, 41 silica. B.B. whitens, and fuses on edges. Decomposed by s. acid, leaving the silica in scales. Pargas (Finland), Fassa Valley, New York, Canada, Ceylon. Char acteristic of serpentine and of dolomitic limestones. 517. ZlNNWALDITE. Oblique prismatic. Forms as in figs. 490, 491 ; also 2Poo (H) and 3P C 3 (a;). m:c 98 to 99. Divergence of optic axes 65. G. = 2 82 to 3 2. C.c. similar to muscovite (sp. 519), but with 4 to Fig. 490. Fig. 491. 8 fluorine, 2 to 5 lithia, and traces of rubidium, cresium, and thal lium. Altenberg and Zinnwald, St Just and Trewavasiu Cornwall. Cryophyllite from Cape Ann in Massachusetts is similar. 518. LEPIDOLITE. Oblique prismatic. Forms like muscovite. Divergence of optic axes 50&quot; to 77. Cl. basal, perfect. H. =2 5 to 4; G. =2 84 to 3. Often massive; scaly granular, coarse or fine. Lustre pearly. Colour rose-red, violet, lilac, yellow, greyish white. Contains 5 to 6 per cent, lithia, with rubidium, caesium, and thallium, also fluorine. B.B. colours flame red. Mourne Mountains, Rozena (Moravia), Uto (Sweden), Ekaterinburg, Maine. 519. MUSCOVITE (Muscovy-Glass), 3 A lSi + KS i. Right prismatic, with monoclinic habit. OP(c); ooP(37); ooP c oo (b); P (m); 2P c oo (y). ooP nearly 120. Twin-face c. Cl. basal, perfect ; elastic. Angle of optic di vergence from 44 to 77. Metallic, pearly. Colourless, and tinged of various shades to black. B.B. fuses to an opaque enamel. Not affected by acids. C.c. : 36 6 alumina, 11 8 pot ash, 45 1 silica, 4 5 water, with traces Fig. 492. of fluorine. Shetland, Loch Glass in Sutherland, Glen Skiag (crystals 15 inches in length) and Struay Bridge in Ross, Aber deen, Cornwall, St Gotthard, Norway, Sweden, Siberia. Crystals over a yard in diameter in China, where it is used for windows. Ftichitc, bright green, has 6 per cent, of chrome oxide. Margaro- dite contains 4 to 6 water. Gilbertitc, Cornwall, may be different. 520. PARAGONITE (Soda-Mica), 2A.. 2 Si 3 + (Na, ft)Si. Massive; foliated. Lustre pearly. H. =2 5 to 3 ; G. -278 to2 9. Yellowish, greyish, and greenish. C.c.: 40 1 alumina, 6 1 soda, 4775 silica, 4 6 water. Monte Campione, St Gotthard. 521. SANDBERGEKITE (Baryta- Mica). White minute scaled aggregates. G. =2 894. C.c. : 30 2 alumina, 4 9 magnesia, 5 9 baryta, 76 potash, 42 6 silica, 4 43 water. Pfitsch Valley in Tyrol, and the Swiss Alps. 522. MARGAKITE (Lime-Mica). Right prismatic. Cl. basal perfect. H. =3 5 to 4 5; G. =2 99 to 3 1. Lustre of cl. pearly. Lateral planes, vitreous. Snow-white, reddish white, and pearl-grey. Laminae brittle. Optic axial angle 109 to 129. C.c.: 51 2 alumina, 1T6 lime, 2 6 soda, 301 silica, and 4 &quot;5 water. Grciner in Tyrol, Naxos, Asia Minor, Greece, Pennsylvania, North Carolina. Diphanite is similar. 523. EUPHYLLITE ( Jft 3 + g SJ-jSig + ^H . Like muscovite, but laminae not easily separable. H. =3 &quot;5 to 4 5; G. =2 83 to 3. Lustre of cl. pearly to adamantine. White to colourless. Transparent to opaque. Laminae brittle. Optic axial angle 71^. C.c.: alumina 42 3, lime 15, potash 3 2, soda 5 9, silica 41 6, water 5 5. Unionville in Pennsylvania. 524. CLINTONITE, (f R 3 + f Al) 2 Si + jft . Oblique prismatic; in hexagonal tables, or massive foliated. Cl. basal, perfect. H. =5 to 5 - 5; G. =3 15. Translucent; pearly to metallic on the cleavage. Angle of the optic axes 3 to 13. Reddish brown to yellow. C.c.: 397 alumina, 21 1 magnesia, 13 1 lime, 19 &quot;2 silica, 2 protoxide of iron, 4 9 water. Amity and War wick in New York. Brandisite is similar. 525. XANTHOPHYLLITE. Oblique prismatic, C about 90. Crystalline aggregates. Radiate lamellar. H. = 4 5to 6; G. =3 1. Lustre pearly. Colour yellowish to copper-red. Angle of optic axes to 20. C.c. : alumina 43 6, lime 13, magnesia 17 5, silica 16 9, water 5 1. Zlatoust. 526. CHLORITOID, FeSi + AlH. Right prismatic ; in foliated crystals ; brittle. Cl. basal. Lustre greasy to pearly. H. =5 5 to 6 ; G. =3 52 to 3 56. Dark green ; streak greenish white. C.c.: 40 alumina, 27 protoxide of iron, 25 silica, 7 water. B.B. infusible, but becomes magnetic. Decomposed by s. acid. Hillswick in Shetland, Pregratten in Tyrol, Ekaterinburg, Canada. 527. MASONITE. Broad plates. H. =6 5; G. =3 53. Grey -green. Streak grey. Pearly to vitreous. C.c.: 26 4 alumina, 19 peroxide of iron, 167 protoxide of iron, 32 68 silica, 4 5 water. Middletown in Rhode Island. 528. OTTRELITS, Al 2 Si 3 + 3(Fe, Mn)Si + 3H. Thin hexagonal tables. Cl. parallel to the prismatic faces. H. = 5 5 ; G. =4 4. Translucent; vitreous. Greenish or blackish grey. C.c. : 24 - 3 alumina, 16 8 protoxide of iron, ll l protoxide of manganese, 43 4 silica, 5 65 water. Ottrez in the Ardennes (Luxemburg), Aste in the Pyrenees, Ebnat in Bavaria, Newport (Rhode Island), Vardhos (Greece). 529. PYROSMALITE, Hexagonal. P 101 34 ; crystals ooP, OP; tabular; also granular. Cl. basal, perfect ; brittle. H. =4 to 4 5 ; G. =3 to 3 2. Trans lucent to opaque ; resinous, or metallic-pearly. Liver-brown to olive-green. C.c.: 35 5 silica, 27 5 iron protoxide, 21 - 5 manganese protoxide, 8 chloride of iron or manganese, and 7 5 water. Nord- mark in Sweden. 530. ASTROPHYLLTTE, (K 3, Right prismatic, with oblique&quot; habit. In long tabular prisms, and in stellate groups. Cl. basal, perfect. H. =3 5; G. =3 33. Submetallic to pearly. Tombac-brown to gold-yellow. Pellucid. Axial divergence 118 U to 124. C.c. : peroxide of iron 9 3, protoxide 23 6, protoxide of manganese 10, soda 3 9, potash 5 9, titanic acid 7 90, silica 39 2. Brevig, El Paso in Colorado. CHLORITE GROUP. Fig. 493. 531. CHLORITE, 2RSi + R.,Al + 3H : . Hexagonal. P 106 50 ;&quot; crystals tabular of OP, ooP or OP, P (fig. 493) ; often in comb-like or other groups ; generally foliated andscaly. H. =1 to 1 5; G. =278 to 2 96. Leek-green to blackish green ; streak greenish grey. C.c.: 21 alumina, 20 protoxide of iron, magnesia 18, silica 24, water 11. Tarf- side, Bute, and Jura in Scotland. Cornwall, Cumberland, Wales, Fassa Valley, Urals, America.