410 MINERALOGY 96 40 , OP (J/), Poo (r ooPoo (T). M : T 115 , T:n 111 21 , T: d 130 18 . Often massive or granular; fracture conchoidal. H. = 6 ; G. =3 4 to 3 8. Translucent on edges ; vitreous to resinous. Black to brown or greenish ; streak brownish grey. B. B. froths and melts to a brown glass. Gelatinous with h. acid. C.c.: 12 to 18 alumina with peroxide of iron, 13 to 26 oxide of cerium and lanthanum, 2 to 12 yttria, 4 to 20 protoxide of iron, 30 of silica. Small crystals common in the syenitic granites of Scotland ; as at Lairg, Boat of Garten (fig. 463), Aboyne, and Criffel. In lime stone at Urquhart (fig. 462), Greenland, Hittero and Snarum, Thuringia, Pennsylvania, New Jersey. Orthite (massive) at Finbo, Kragero, and Falun. Oerine (granular) at Riddarhyttan. Pyr- orthite has carbonaceous matter. Bodenite is a variety. 475. IDOCRASE, 3(Ca, Mg) 3 Si + 2AlSi . Pyramidal ; P (c) 74 27 (figs. 464 to 466). Crystals ooP (d), Fig. 464. Fig. 465. Md 6 to 7; G. =3-2 to ooPoo (M], P (c), OP (p), Poo (o) 56 29 , ooP2 (/). Prismatic, striated ; also granular ; fracture uneven. H. = 6 5 ; G. =3 35 to 4. Pellucid; vitreous to resinous. Brown, green, yellow; streak white. B.B. fuses easily, with intumescence, to a green or brown glass. Partially sol. in h. acid ; after ignition totally, gelatinizing. C.c. : alumina 16, peroxide of iron 7, lime 34, silica 38. Glen Gairu and Crathie, Aberdecnshire, in lime stone ; Broadford, Skye ; Wicklow and Donegal, Ire- ^-^^ land ; Egg, Norway ; Mussa, Piedmont ; Vesuvius ; Fig. 466. Wilui river, near Lake Baikal (fig. 463). Cyprinc from Thele- mark is azure-blue, from copper. OLIVINE GROUP. 476. FORSTERITE, Mg 2 , Si. Right prismatic. Like olivine (sp. 478). 3 3. Vitreous ; transparent. White, wax- yellow, greenish ; streak white. C.c. : magnesia 57 1, silica 42 86. Vesuvius. Boltonite, red, is from Massachusetts. 477. FAYALITE, Fe 2 Si. Right prismatic ; n : n 49 36 (fig. 467). Massive. Cl. rectangular. Black, green ish, or brownish. Metallic to resinous : fracture conchoidal ; magnetic. H. = 6 5 ; G. =4 to 4 1. C. c. : protoxide of iron 70 - 5, silica 29 - 5. Mourne Mountains, Ireland ; Fayal, Azores. 478. CHRYSOLITE (Olivine, Pcridote), (Fe, Mg) 2 Si . Right prismatic. 139 54 ; middle 108 P (c) 30 . 85 16 and Fi S 467 ( s ^ 477 ) ooP (n) 130 2 , Poo (d) 76 54 , 2Poo (k) 80 53 , oo Poo (J/) (fig. 468). Also massive. Cl. brachy- diagonal, perfect ; fracture conchoidal. H. =6 5 to 7; G. =3 3 to 3 5. Trans parent ; vitreous. Olive-green, yellow, brown, and colourless. B.B. infusible. Soluble, with gelatinizing, in acids. C.c. : 47 magnesia, 12 protoxide of iron, 40 silica. Talisker in Skye, Haalival in Rum, Elie in Fife, Unkel on the Rhine, Vesuvius, Esneh in Egypt, Brazil. Hya- losiderite, brown and yellow, with metallic * lustre and 30 per cent, protoxide of iron, is from the Kaiserstuhl in the Breisgau. 479. TEPHROITE, Mn 2 Si . Fig. 468 (sp. 478). Right prismatic ; granular, with rectangular cleavages. Ash- grey, rose-red. Adamantine; translucent. II. =5 5 to 6; G. =4 to 41. C.c. : protoxide of manganese 70 2, silica 29 8. Franklin and Sparta in New Jersey. 480. KNEBELLITE, FeJSi Massive. Grey, brown, green, black. Glistening ; brittle. H. =6 5; G. =3 71. C.c. : protoxide of iron 35 5, protoxide of manganese 35, silica 29 5. llmenau, Dannemora in Sweden. 481. MONTICELLITE, Ca 2 Si + Mg 2 Si . Right prismatic. P (/) 110 43 and 97 55 , coP ( s ) 98 7 , ooP2 () 133 6 , Poo (k) 81 57 , |Poo (h) 120 8 , P2 (e) 141 47 and 82, ooPoo (6) (fig. 469). Vitreous. Grey, yellowish and greenish, and white ; streak white. Translucent. H. = 5 to 5 5; G.= 3 to 3 -25. C.c. : lime 35, magnesia 21 9, protoxide of iron 5 "6, silica 3 7 5. Sol. in h. acid, gelatiniz ing. Somma (Milan). 482. CHONDRODITE (ffumite), Mg 5 S io . Od Right prismatic. P middle edge 156 38 , polar edges 131 34 and 54 28 (figs. 470 to 472). Crystals monoclinic in habit, often granular- massive. H. = 6-5 ; G. =3 15 to 3 -25. Fig. 469 (sp. 481). Translucent ; vitreous to resinous. Yellow, red, brown, green, and black ; streak white. B. B. infusible. Decomposed by acids. C. c. : Fig. 470. Fig. 471. Fig. 472. silicate of magnesia, with 2 to 3 of fluorine. From limestone on Loch Ness (?); Pargas, Finland; Gallsjo and Aker, Sweden ; Ni-w York ; Sparta, New Jersey. Humitc, from Somma. 483. LIEVRITE, 3(Fe, Ca) 2 Eight prismatic. P (o) polar edges 139 30 and 117 27 ; oop 112 38 , Poo (d) 112 49 , oo P2 (s) 106 15 . Crystals (fig. 124) are long-prismatic and vertically striated ; also radiated, columnar, or fibrous ; brittle. H. =5 5 to 6 ; G. =3 9 to 4 2. Opaque ; resinous or imperfect metallic. Brownish or greenish black ; ttreak black. B. B. fuses easily to a black magnetic globule. Sol. in h. add, forming a yellow jelly. C.c.: 29 "3 silica, 19 6 iron peroxide, 35 2 iron protoxide, 13 7 lime, and 2 2 water. Piio in Elba, Fossum, Kupfrrberg, Rhode Island, and Greenland. 484. CEKITE (Ce, R) 2 Si + H. Hexagonal ; OP; ooP; in low six-sided prisms. Generally fine- granular ; fracture uneven, splintery; brittle. H. = 5 5; G. =4 9 to 5. Translucent on the edges ; dull, adamantine, or resinous. Clove-brown, cherry-red, or pearl-grey. Sol. in h. acid, leaving gelatinous silica. C.c.: 20 5 silica, 73 5 protoxide of cerium (with didymium and lanthanum), and 6 water. Bastnaes near Riddar- hyttan. 485. GALMEI, Zn 2 Si + H-. Right prismatic, and hemimorphic ; 2P2 (P) with polar edges 101 35 and 132 26 , ooP (d) 103 50 , Poo (o) 117 14 , Poo ( l) 128 55 (fig. 46); common form ooPoo (s), ooP, poo. Also columnar, fibrous, granular, and earthy. Cl. prismatic along ocP, very perfect; along Poo perfect. H. =5; G. =3 "3 to 3 5. Trans parent to translucent ; vitreous and pearly. Colourless or white, but often light grey, also yellow, green, brown, and blue ; becomes electric by heat. B. B. decrepitates slightly, but is infusible ; with cobalt solution blue and partly green ; readily soluble in acids, and gelatinizes. C.c. : 25 silica, 67 5 zinc oxide, and 7 5 water. Wnn- lockhead, Mendip Hills, Matlock, Raibl and Bleiberg in Carinthia, Aix-la-Chapelle, Iserlohn, Nertchinsk, Pennsylvania, Virginia. Used as an ore of zinc. WlLLEMITE GROUP. 486. WILLEMITE, ZnjSi . Rhombohedral ; R 116 1 . Cl. basal, and prismatic, ooR ; brittle. H. =5 5 ; G. =3 9 to i 2. White, yellow, brown, and red. Vitreous lustre. C.c. : oxide of zinc 73, silica 27. Altenberg,
Liege, Greenland, New Jersey.