Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/429

Rh MINEKALOGY 411 487. TROOSTITE, ZnSi + MnS i. Rhombohedral ; R 116. Cl. prismatic, oP2 ; brittle. H. = 5 5 ; G. 41. Asparagus-green, grey, and reddish brown. Vitreous. C.c. : oxide of zinc 58, oxide of manganese 13, silica 28. New Jersey. 488. CENTROLITE (PbMn) Si. Right prismatic; ooP 115 18. Form oP, P, oofoo. H. =5; G. =6 2. Red-brown. Cl. prismatic ; splendent on P. Southern Chili. 489. PHENACITE, Gl 2 Si. Hexagonal and tetartohedral ; R (p) 116 36 (fig. 473V Crystals R, oo P2, P2. Twins with parallel axes, and intersecting. Cl. R, and ooP2 ; fracture con ch oidal. H. =7 5 to 8; G. = 2 - 97. Transparent or trans lucent ; vitreous. Colourless, and wine-yellow or brown when fresh, but colour soon lost on exposure. B. B. infusible ; not affected by acids. C.c. : glucina 45 &quot;8, silica 54 &quot;2. Framont in Alsace, Takovaya in Urals, Miask, Durango in Mexico. 490. DIOPTASE, CuSi + H. Hexagonal and rhombohe- dral ; R 125 54, - 2R (r) 95 28 , ooP2, - 2R (a) (fig. 474). Cl. R, perfect ; brittle. H. = 5 ; G. translucent; vitreous. Emerald-green, rarely verdigris-green or blackish green ; streak green. C. c. : 38 7 silica, 50 copper protoxide, and 11 3 water. Altyn-Tiibeh in the Kirghiz Steppe, Murosh- naya, Copiapo. 491. CHRYSOCOLLA, CuSi + 2H. Botryoidal or investing ; brittle ; fracture conchoidal. H. = 2 to 3 ; G. = 2 to 2 3. Trans lucent ; resinous. Verdigris- to emerald-green or azure-blue ; streak greenish white. C.c.: 34 - 83 silica, 44 94 copper protoxide, and 20 23 water. Leadhills, Lackentyre in Kirkcud bright, Cornwall, Saxony, Hungary, Spain, Urals, Australia, Chili. 492. BOGOSLOVSKITE (Kupfcrblau). Massive; fracture conchoidal; brittle. H. = 4 to 5 ; G. = 2 - 56. Sky- to ultramarine-blue ; streak smalt-blue, and shining. A silicate of copper, with 45 - 5 per cent, copper oxide. Schapbach Valley in Baden, Bogoslovsk in the Urals. Demidowitc may be the same. Fig. 473 (sp. = 3 2 to 3 3. Transparent or Fig. 474 (sp. 490). GARNET GROUP. 493. GARNET, B 3 Si 2 + SSi. Cubic ; most common forms ooO and 202 (figs. 33, 40, 60, 475). Also granular. Cl. dodecahedral ; fracture conchoidal, or splintery. H.=6 5 to 7-5; G. =3 5 to 4 &quot;3. Pellucid; vitreous or resinous. Rarely colourless or white ; generally red, brown, black, green, or yellow. B. B. in general fuses to a glass, black or grey in those containing much iron, green or brown in the others, and often magnetic; imperfectly soluble in h. acid. C.c. ex ceedingly variable, but generally forming two series, according as R 2 3 is chiefly alumina or chiefly iron peroxide ; and these are again divided according as RO is more especially lime, iron pro toxide, magnesia, or a similar base. The more important varieties are Fig. 475. (1) Lime- Alumina Garnet, Ca^S ig + AlSi, with 40 silica, 23 alumina, and 37 lime. To this subdivision belong (a) Water Garnet. Colourless to white. Craig Mohr, Aberdeen ; Thelemark in Norway. (b) Grossular. Olive- to gooseberry-green. Craig Mohr ; Wilui river ; America. (c) Cinnamon Stone. Hyacinth-red to orange-yellow. Glen Gairn (Aberdeen), Allt Gonolan and Ord Ban (Inverness), Ceylon, Wermland. Romanzowitc, from Kimito (Finland), is the same. This variety when polished is often sold as Hyacinth. (d) Common Lime Garnet. Here one half of the alumina is replaced by iron peroxide. Colours red, brown, yellow. Piedmont, Vesuvius, the Urals. (2) Magnesia- Alumina Garnet ; RO chiefly magnesia. Arendal. (%} Manganese- Alumina Garnet; RO = MiiO; reddish-brown. Spessart (Bavaria), Sweden. (4) Marjncsia-Iron-Limc- Alumina Garnet, Pyropc. Colour port- wine to purplish red. Elie in Fife, Zoblitz in Saxony, Bohemia. (5) Iron-Alumina Garnet, Almandine, Noble Garnet. Colum bine-red, inclining to violet, blood-red, and reddish brown. Common in mica-slate, gneiss, and granite. Shetland, Ross, Inverness, Aberdeen, Falun, Arendal, Tyrol, the Urals, North America, Pegu, and Ceylon. (6) Lime-Chr(nne- Alumina Garnet, C-a 3 Si a + (6r, Al)Si, Uivaro- wite. Emerald-green ; with 22 per cent, chrome oxide. Bissersk and Kyshtimsk in the Urals, India, and California. (7) Lime and Iron Garnet, Ca 3 Si 2 + Fe, Si. This includes (a) Common Iron-Garnet, Rothojfite, Allochroitc. Subtranslucent or opaque. Green, brown, yellow, or black; with white, grey, or yellow streak. Sweden and Arendal. (b) Melanite. Black; opaque; in thin splinters translucent; streak grey ; slightly magnetic. Albano near Frascati, Vesuvius, France, Lappmark. (c) Colophonite. Yellowish-brown to pitch-black, also yellow or red; resinous; streak white. G. =3 43. Arendal. The red varieties, when cut en cabochon, are termed Carbuncles. 494. AXINITE, (Al, B) Si + 2(Ca, Fe)Si. Anorthic. Crystals unsymmetrical. u : P 135 31 ; u : r 115 38, P:r 134 45 (figs. 136, 137). Cl. distinct along planes trun cating the sharp edges between P and u and P and r. H. = 6 5 to 7; G. =3 2 to 3 3. Pellucid; vitreous. Clove-brown, inclining to smoke-grey or plum-blue ; but often cinnamon-brown in one direc tion, dark violet-blue in a second, and pale olive-green in a third (trichroism). B. B. colours flame green ; intumesces, and fuses easily to a dark green glass, becoming black in the ox. flame ; ot sol. in li. acid till after ignition, when it gelatinizes. C.c.: 45 - 9 silica, 5 9 boracic acid, 17 5 alumina, 9 3 iron (with manganese) protoxide, and 21 4 lime. Botallack and other mines in Cornwall, Bourg d Oisans in Dauphine, Kongsberg, Arer.dal, Nordmark in Sweden, Pyrenees, St Gotthard, Tyrol, Thum in Saxony, Urals, and North America. 495. DANBURITE (Ca, B) 2Si. Right prismatic. ooP(7) 122 52, &amp;lt;xP2 (&amp;lt;?) 94 52 , Poo (d) 97 7, 4P (w) 54 58 , OP (c), P (o), 2P2 (r), oopoo , &amp;lt;xP4 (n). Fig. 476. Fig. 477. Fig. 478. Fig. 479. Cl. basal ; fracture uneven to subconchoidal ; vitreous to greasy lustre. H. =7 to 7 5; G. =2-986 to 3-021. Pale yellow to reddish brown. Translucent ; brittle. C.c. : 22 76 lime, 28 &quot;46 boracic acid, 4876 silica. Danbury in Connecticut, Russell in New York. HELVINE GROUP. 496. HELVINE, MnS + 3R 2 Si. Cubic and tetrahedral. or -jr- - ^- (fig. 64 and with 66). Im- 2t Mm bedded or attached. Cl. octahedral. H. =6 to 6 5 ; G. = 31 to 3 3. Translucent on the edges; resinous. Wax-yellow, siskin- green, or yellowish brown. B.B. in the red. flame fuses with in tumescence to a yellow obscure pearl ; sol. in h. acid, evolving sulphuretted hydrogen, and gelatinizes. C.c. : 34 silica, 10 glucina, 8 iron protoxide, 43 manganese protoxide, and 5 sulphur. Schwarz- enberg in Saxony, and near JVIodum in Norway. 497. DANALITE, 3R 2 Si + ZnS. Cubic. In octahedra, with striated dodecahedral planes. H. - 5 5 to 6 ; G. =3 43. Vitreous to resinous. Flesh-red to grey ; streak lighter. Translucent ; brittle. C.c. : protoxide of iron 29, of manganese 6 5, of zinc 19, silica 31 5, sulphur 5 5. Reckport in Massachusetts. The crystals (fig. 66) 498. EULYTINE, BLjSis. Cubic and tetrahedral. 2 ~ and - small, and often with curved faces ; fracture conchoidal. H. = 4 &quot;5 to 5; G. =5 9 to 61. Transparent and translucent ; adamantine. Clove-brown, yellow, grey, or white; streak white or grey. C.c.: 16-2 silica and 83 8 bismuth peroxide. Schneeberg and Brauns- dorf near Freiberg.