Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/426

Rh 408 MINEKALOGY 449. ZWIESELITE, (Fe, M Eight prismatic ; but only massive. Cl. basal, perfect. H. =4 5 to 5; G. -=3 95 to 4. Brown; streak yellow. C.c. : like triplite. Zwiesel in Bavaria. 450. AMBLYGONITE, A l 5 P ;t + (Li, &a),i+MF s + (Li, Na)F. Anorthic; crystals rare; coarse granular. Cl. OP, pearly, meeting two others at 105* and 87&quot; 40 . Fracture uneven and splintery. H. =6; G. =3to3 l. Translucent; vitreous. Greyish or greenish white to pale mountain-green. C.c.: 47 9 phosphoric acid, 34 5 alumina, 6 9 lithia, 6 soda, and 8 3 fluorine. Penig, Arendal, Montebras (Creuse, France), also Hebron and Paris in Maine. Montebrasite has no soda. 451. DURANGITE, (iy A s + 2NaF. Oblique prismatic; crystals like keilhauite (sp. 669). ooP 110 10 ; P 112* 10. Cl. prismatic. H. =5; G. =3 95 to 4. Bright orange-red; streak cream-yellow. Vitreous. C.c. : alumina 17 2, iron protoxide 9 2, arsenic acid 53, soda 13 1, fluorine 77. Durango (Mexico). 452. HERDERITE. Right prismatic. P polar edges 77* 20 and 141* 16 ; ooP 115 53 . Fracture conchoidal. H. =5; G. =2 9 to 3. Translucent; vitreous, inclining to resinous. Yellowish or greenish white. Ehrenfriedersdorf in Saxony. An anhydrous phosphate of alumina with lime and fluorine. PHOSPHATES WITH SULPHATES AND BORATES. 453. SVANBERGITE. Rhombohedral ; R 90 35. H. = 4 5; G. =2 57. Vitreous to adamantine. Honey-yellow, reddish brown, and rose-red ; streak reddish. Subtransparent. C.c.: 37 8 alumina, 6 lime, 17 3 sul phuric acid, 12 8 soda, 17 8 phosphoric acid, 6 8 water. Horr- sjoberg in Wermland. 454. DIADOCHITE, Fe. 3 ? 2 + 2FeSJ + 32H. Reniform and stalactitic ; fracture conchoidal. H. =3; G. =1 9 to 2. Resinous ; vitreous. Yellow or yellowish brown; streak white. C.c. : 36 7 iron protoxide, 14 8 phosphoric acid, 15 2 sulphuric acid, and 30 3 water. Graf en thai and Saalfeld. 455. PITTICITE, Fe 2 Ss + 2FeA s+-24H. Reniform and stalactitic ; brittle; fracture conchoidal. H. =2 3; G. -=2 3 to 2 5. Translucent throughout, or on the edges ; resinous to vitreous. Yellowish, reddish, or blackish brown, sometimes in spots or stripes; streak light yellow or white. C.c.: 35 iron per oxide, 26 arsenic acid, 14 sulphuric acid, and 24 water. In many old mines, as Freiberg and Schneeberg. 456. BEUDANTITE. Rhombohedral ; R 91* 18. H. = 3 5; G. -4. Vitreous. Olive- green; streak greenish yellow. C.c.: oxide of iron 40 69, oxide of lead 24 OS, sulphuric acid 1376, phosphoric acid 8 97, water 977. Dornbach in Nassau, Cork iu Ireland. 457. LUNEBURGITE (2Mg, H) P + Mg fi + 7H. Concretions of fibrous structure. C.c.: 25 2 magnesia, 29 83 phosphoric acid, 1474 boracic acid, 30 - 23 water. Liineburg. ARSENITES. 458. ECDEMITE, P&quot;b s As a + 2PbCl 2. Pyramidal. Cl. OP. H. =2 5 to 3; G. =714. Pale green. Vitreous on cleavage ; resinous on fracture. C.c. : oxide of lead 59 67, Iead22%arseniousacid 10 59, chlorine 7 58. Laagban in Wermland. 459. TRIPPKEITE, CuAs. Pyramidal; P 111* 56. Blue-green. Lustrous. Copiapo in Chili. SILICATES. ANDALUSITE GROUP. 460. ANDALUSITE, AlSi. Right prismatic. ooP ( m ) 90* 50, P (r) 109 4 , Poo (s) 109 51. Fig. 446. Fig. 447. Also columnar. Cl. m; fracture splintery. H. =7 to 7 -5; G. =3 1 to 3 2. Pellucid; vitreous. Grey, green, red, or blue. B. B. infusible. Not affected by acids. C.c. : alumina 63 1, silica 36 9. Clashnaree (figs. 446 to 449) and Clovain Aberdeenshire, Marnoch and Botriph- Fig. 448. Fig. 449. nie in Banffshire, Killiney Bay in Wicklow, Andalusia, Tyrol, Penig, Massachusetts, Litchfield in Connecticut. Chiastolite. H. =5 to 5 5; G. =3. Pale grey, yellow, green, and red. A compound structure, formed of four double wedge-shaped crystals, arranged in contact with the angles of a square conoidal crystal placed in their centre, and imbedded in a paste of clay slate. The section of the compound structure forms a tesselated cross, the appearance of which varies with the portion of the crystal which is cut. Portsoy (fig. 450) and 450. Fi Boharm in Banffshire, Wicklow, Keswick and Skiddaw, Brittany, Pyrenees, Maine, New Hampshire, Nova Scotia, Canada. 461. CYANITE (Disthene), A lSi. Anorthic ; generally broad-prismatic lengthened crystals, formed by two faces (m, t). m: t 106 15 ; m : i 145 41 ; p : m 93 15 (fig. 451). Hemitropes common, united by m. Also radiated. Cl. m, perfect; brittle. H. = 7, on cl. planes 5 ; G. = 3 5 to 37. Pellucid; vitreous. Cl. pearly. Colourless, and red, yellow, green, grey, and blue. B.B. infusible. Not affected by acids. C.c. same as andalusite. Hillswick in Shetland, Mount Battock, Tarfside (fig. 451), Botriphnie (Banffshire), Tyrol, St Gotthard, Bohemia, Pontivy in France. 462. SlLLIMANITE, AlSl. Right prismatic ; ooP 111. Crystals fibrous, columnar, and radi ating. Cl. macrodiagonal. H. =7; G. =3 2 to 3 26. Translucent; resinous ; on cl. vitreous. Greyish, greenish, clove, or hair-brown. C.c. and chemical characters like cyanite. Tvedestrand, Norway; Chester and Norwich, Connecticut. Al 2 3 ,Si0 2 is thus trimorphous. Atonrolite, Xenolite, Bucholzite, Fibrolite, and Bamlite are varieties. 463. TOPAZ, 5AlSi + AlF 3 + SiF 2. Right prismatic. ooP (M) 124 17, 2Po (n) 92 42 , ooP2 (I) 93&quot; 14, P (o). Crystals always prismatic (lig. 122), often hemimorphic. Cl. basal, perfect; fracture conchoidal. H. =8; G. =3 4 to 3 6. Transparent ; vitreous. Colourless, honey-yellow, amber, pink, asparagus-green, blue. Becomes electric by heat or friction, and the yellow colours become pink. B.B. infusible. Not affected by h. acid ; by digestion in s. acid gives traces of fluorine. The formula requires 33 2 silica, 567 alumina, 17 5 fluorine. Part of the oxygen must be replaced by fluorine, as the total of the above is 107 4. Ben-a-bourd and Arran, Scotland ; Mourne Mountains, Ireland; St Michael s Mount, Cornwall; Siberia, Saxony, Bohemia, Connecticut, Australia, Ceylon, Brazil, Peru. The finest topazes are the blue from Scotland and Siberia, the pink, the yellow from Brazil, and the colourless from Peru. The lust-named when cut may be distinguished at once from diamond by their elec tricity. Pyrophysalite is a massive opaque cleavable variety from Falun. Pycnite is a columnar straw-yellow to reddish white variety from Zinnwald in Saxony and Durango in Mexico. 464. STAUROLITE, (Al, Fe)Si + (Fe, Mg) Si. Eight prismatic. ooP (m) 128 42 , Poo (r) 70 46, ooPoo (o), OP (p) (fig. 452). Twins common, as figs. 140, 144, 187, 453. Cl. brachydiagonal, perfect ; fracture conchoidal to splin- tery. H. -7; G. -8 5 to 3 -8. Trans- Fi S- 452 - (Sp- 464.) Fig. 453. parent to opaque ; vitreous to resinous. Reddish brown : streak white. B. B. infusible. Not affected by h. acid, partially by s. acid.