Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/427

Rh MINERALOGY 409 C.c. : silica 30, alumina 48 5, with 5 5 iron peroxide, 12 5 iron protoxide, 3 5 magnesia ; often impure. Bixeter Voe and Unst in Shetland, Boharm and Marnoch in BanfTshire, StGottliard, Greiner in Tyrol, Finistere, Urals, and North America. Xantholite is a yellow variety from Urquhai t (Inverness). 465. SAPPHIRITE, 4Mg, 5A1, 2Si. Oblique prismatic; granular. H. -7 to 8; G. 3 4 to 3 5. Vitreous; pale blue or green; translucent; dichroic. C.c. : alumina 63 &quot;2, magnesia 19 3, silica 14 9. Fiskenaes in Greenland. TOURMALINE GROUP. 466. TOURMALINE, EgSi+ SSi. Rhombohedral ; R 133 10. Crystals of OR, - $R; usually long prismatic, and striated (fig. 45, and 249 to 252). Generally hcmimorphic ; also radiating and fibrous ; fracture conchoidal to uneven. H. 6 5to7 5; G. =3 to 3 3. Black varieties opaque, others transparent ; vitreous. Generally black ; but colourless, yellow, brown, blue, green, and rose-red; streak white. Different colours often disposed in layers parallel to the axis; and portions of one crystal differing also in colour along the axis. By friction acquires positive electricity; and becomes elec trically polar when heated. Powder insol. in h. acid ; imperfectly in s. acid. C.c. complex, but all with water and fluorine, some with boracic acid. Coarse black columnar varieties, railed Schorl, very common in granite and gneiss. Black occur at Portsoy in Banff, Clova, Cabrach, and Rubislaw in Aberdeenshire, Bovey in Devon shire, St Just in Cornwall, in Greenland, Arendal, Tyrol, and North America ; blue or Indicolite at Uto in Sweden ; green at Glen Skiag in Cromarty. Crystals ruby-red within, surrounded by green or red at one extremity and green at the other, also blue and pink, at Albany, Paris, and Hebron in Maine. Currant-red or Eubellite in India and Ceylon, also in Siberia and Brazil. 467. DATHOLITE, Cafi + CaSi 2 + H-. Oblique prismatic, C 89 51. ooP (g) ]15 22, ooP2 (/) 76 38 , P (P) 120, - Po (a) 45 8, ooPoo (s), 2P c oo (o) (fig. 454) ; or rhombic with 6:/90, b:al 65 a, b:c 141 9 , and f:g 160 39. Fracture uneven, or conchoidal. H. -= 5 to 5 5 ; G. = 2 9 to 3. Transparent or translucent ; vitreous. Colourless and tinted green ish, yellowish, or pink. In closed tube yields water. B.B. intumesces and melts easily to a clear glass, colouring the flame green; the powder gelatinizes in h. acid. C.c.: 38 1 silica, 21 6 boracic acid, 3 4 7 lime, and 5 6 water. Bishopton in Renfrew, Glen Farg in Perthshire (fig. 455), Salisbury Crags and Corstor- phine Hill near Edinburgh, Arendal, Uto, Andreasberg, Seisser Alp, Connecticut, and New Jersey. Figs. 238, 239 are pseudomorphs of quartz after datholite termed Jfaytorite. 468. EUCLASE, 2GlSi + A1H. Oblique prismatic, C 79 Fig. 455 (sp. 467). 4t. ooP c 2 (s) 115; 3P C 3 (/) 105*49 . Crystals specially of &amp;lt;x&amp;gt;r2, o&amp;gt;P c oo (T), 3P C 3. Cl. clino- diagonal, perfect ; very brittle and fragile ; fracture conchoidal. T Fig. 456. Fig. 457. H. =7 5; G. = 3 to 31. Transparent; splendent; vitreous. Mountain-green, passing into blue, yellow, or colourless. B. B. intumesces, becomes white, and melts in thin splinters to a white enamel. Not affected by acids. C.c. : 42 silica, 35 alumina, 18 glucina, 6 water. Peru and Brazil, and Southern Urals. Cannot be used as a gem on account of its brittleness ; whence its name. 469. HOMILITE. Oblique prismatic, C 89&quot; 21. H. -5 5; G. -3 &quot;28. Black and brownish black. Vitreous. C.c.: 27 28 lime, 16&quot;25 protoxide of iron, 31 87 silica, 18 1 boracic acid. Stoko and Brevig (Norway). 470. BOTRYOLITE. Fine fibrous, botryoidal, or reniform. Snow-white to hair-brown. Chemical and physical characters like datholite, but 10 64 of water, being 2 equivalents. Arendal. 471. GADOLINITE, (Y, Ce, Fe).jSi. Oblique prismatic, C 89&quot; 28. ooP 116; P 120 56 (fig. 458). Fracture conchoidal, or splintery. H. =6 5 to 7 ; G. = 4 to 4 4. Translucent on the edges ; vitreous to resinous. Black ; streak greenish grey. B. B. the con choidal (vitreous) varieties incandesce; gelatinizes in h. acid. C.c.: 36 to 51 ** 458 (sp. 4/1). yttria, 10 to 15 iron protoxide, 5 to 17 protoxide of cerium with lanthanum, to 12 glucina, and 25 to 29 silica. Hitterb in Norway, Ytterby, Broddbo and Finbo near Falun. EPIDOTE GROUP. 472. ZOISITE, 4Ca, 3A1, 6Si + H. Right prismatic. ooP 116 26 ; oop&quot;2 145&quot; 24 ; o&amp;gt;P&quot;3 156* 40 ; P&amp;gt; 122&quot; 4 ; 2Poo 1116 (fig. 459). Cl. brachydiag- onal, perfect. H. - 6 ; G. - 3 2 to 3 4. White, brownish grey, and dark green. B.B. intu mesces, and forms a white or yellow porous muss ; and on the edges fuses to a clear glass. C.c.: 29 8 alumina, 24 35 lime, 2 &quot;8 oxide of iron, 40 3 silica, and 2 1 water. Glen Urquhart, Dalnain, and Allt Gonolan, In verness; Sterzing in Tyrol, the Sau Alp in Carinthia, the Urals, and Connecticut. Thutite, peachblossom-red, Irom Souland in Thelemark (Norway), is similar. 473. EPIDOTE, 4Ca, 3A1, 6Si + H. Oblique prismatic, C 89&quot; 27. ooPoo(3/), ooP 2 (o) 63 1, Poo(7 T ) 64 36 , -P (n) 70 Fig. 459 (sp. 472). 25, - Pco (r) 63 42 , P (z) 70*. Crystals complex, with many partial forms. Hemitropes united by T ; also columnar and granu lar. Cl. M, perfect; also T, forming 115 24 ; fracture conchoidal to splintery. H. -6 to 7; G Green to yellowish grey. B.B. fuses and swells to a dark brown slag ; after fusion soluble with gela- tinization in h. acid. C.c. : 27 4 alumina, 8 5 iron peroxide, 23 9 lime, 38 3 silica, l - 9 water. Shetland.G lenelg in I n ver- ness, Tilquilly in Aber deen, in gm-iss; in amyg- 3 2 to 3 5. Pellucid ; vitreous. 46 - daloid in Mull and Skye ; in granite at Cassencary in Kirkcud bright; Arendal, Dauphine, Greenland, the Urals, North America. Wiihamitt from Glencoe is a red, strongly dichroic variety. Pied- montite or Manganese Epidote, brownish violet, from St Marcel, has 20 per cent, of manganese peroxide. 474. ALLANITE (Orthite, Cerine), R 3 S Fig. 462. Fig. 463. Oblique prismatic, C 65*. ooP (z) 70&quot; 48, P (n) 71 27 , - P XVL 52