Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/434

Rh 416 MINERALOGY Phosphoresces with heat or friction ; gelatinizes in h. acid. B.B. difficultly fusible to a semitraiisparent glass. C.c. : 517 silica and 48 3 lime, but with to 2 magnesia and to 2 iron protoxide. Glen Gairn, Crathie, &c., in Aberdeen- shire, Urquhart in Inver ness, Skye, Banat, Finland, Sweden, Vesuvius (fig. 501), North America, Ceylon, Capo di Bove. 567. AUGITE (Pyroxene), KSi = (Ca, Jig, Fe)Si. Oblique prismatic, C 7 4 11. oo P 87 6 ; P (s : s) 120 48 ; - P 131 30 ; 2P (o) 95 48 ; OP; 3P ; ooPoo. In fig. 130 o&amp;gt;P (M), ooPoo (r), ocP oo (l),P(s); also various twins and hemitropes of same form (figs. 191, 502, 503). Almost always prismatic, imbedded, or attached ; also granular, columnar, and scaly. Cl. prismatic along eP (with 50 1 (sp. 566). Fig. 502. Fig. 503. angles of 87 6 and 92 54 ), generally rather imperfect ; ortho- diagonal and clinodiagonal imperfect. H. =5 to 6 ; G. =3 to 3 5. Pellucid in all degrees; vitreous; in some pearly on ooPoo. Colour less, and white, but usually grey, green, or black. B. B. generally fusible; imperfectly soluble in acids. C.c. generally as follows : Silica. Lime. Magnesia. Iron. (a) Magnesia augite (6) Magnesia-iron augite 56-22 52-72 25-S4 23-81 18-24 8-50 14-97 49-06 22-29 28 65 Analysis gives 47 to 56 silica, 20 to 25 lime, 5 to 15 magnesia, 1 to 20 iron protoxide, with to 3 manganese protoxide and to 8 alumina. The alumina, chiefly found in very dark green or black augites, may in some replace either silica or part of the silicate. The more important varieties are Diopside. Greyish or greenish white, to pearl-grey or leek-green; streak white. Crystallized or broad columnar, or concentric lamellar. Transparent to translucent on the edges. Not affected by acids. B.B. fuses to a whitish semitraiisparent glass. C.c.: generally lime 26 and magnesia 18 5, with 55 5 silica. Mussa Alp (Massite] and Ala (Alalite) in Piedmont, Schwarzenstein in Tyrol, Scandinavia, Finland, Urals, and North America. Malacolite, Sahlite. White, green, rarely yellow, brown, or red; streak white. Translucent, or only on the edges ; vitreous, inclining to pearly. Seldom crystallized, mostly columnar Fig. 505. Fig. 504. er lamellar. B.B. melts to a dark- coloured glass. Malacolite common in primary limestones in Scotland, as at Shinuess, Ludbeg (fig. 505), and Glen Fi S Tilt. Fassa Valley (Fassaite), Piedmont, Arendal, Philipstadt in Sweden; Lake Baikal (Baikalite); near Lake Lherz in the Pyrenees (Lherzolite) ; Sala (or Sahla) in Sweden (Sahlite) ; Shinness (figs. 504, 506), Glenelg, Tiree, in Scotland ; Tyrol ; North America. Coccolite is a granular sahlite or augite. Augite. Leek-green, greenish black, or velvet-black, rarely brown ; streak greenish grey. Vitreous to resinous ; translucent or opaque. Only slightly affected by acids. B.B. fuses to a black, often magnetic glass. An essential component of many rocks, as basalt, dolerite, clinkstone, and augite porphyry ; Germany, Auvergne, Vesuvius; St Kilda, Rum, Tiree, Dalnain, andUrquhart in Scotland. Augite crystals in basalt often contain very many mi- roscopic crystals and glasses ; also pores with fluid carbonic acid. Hudsonite. Cleavable lamellar, and jet-black, with green streak and bronzy tarnish, from the Hudson river ; the most highly ferru ginous variety. Amianthus. Some asbestiform minerals are augite, but the greater number hornblende. Breislackite. Fine yellowish or brown woolly crystals. Vesuvius, and Capo di Bove near Rome. 568. DIALLAGE, (Ca, Mg, Fe) Si. Like augite, and only a variety with very perfect cleavage in the clinodiagonal, which forms with a second cleavage an angle (if 87. Lustre metallic pearly ; colour grey or pinchbeck-brown. H. =4; G. =3 23. B.B. melts easily to a greyish or greenish enamel. C.c.: 50 to 53 silica, 1 to 5 alumina, 15 to 23 magnesia, 11 to 20 lime, and 5 to 20 manganese protoxide. Constituent of the augite rock of the Cuchullins in Skye and of the gabbro of Unst and Ayrshire. Baste in the Harz, Silesia, the Alps, Apennines, and Urals. Vanadine Bronzite, containing soda and vanadic acid, is similar. At Craig Buroch (Bauffshire) diallage passes in paulite. 569. JEFFERSONITE. Oblique prismatic. Cl. prismatic ooP 87 30, and orthodiagonal. H. = 4 &quot;5 ; G. = 3 3 to 3 5. Dark olive-green, brown to black. Lustre greasy. A manganese and zinc augite, with 10 - 2 protoxide of manganese, and 10 - 15 oxide of zinc. Sparta in New Jersey. 570. ACMITE, 2FeSi 3 - Oblique prismatic. Crystals long often acute-pointed prisms. ooP 87 15, ooPoo (r), P(s), 6P (o), - 6P 3(2) (figs. 507, 508). Cl. like augite. H. =6 to 6 5; Nearly Brownish G. =3-4 to 3-6. opaque; vitreous. or greenish black ; streak greenish grey. Imperfectly soluble in acids. B.B. fuses easily to a black magnetic glass. C. c. : 52 silica, 30 iron peroxide, 5 iron protoxide, and 13 soda, but with 1 to 3 manganese peroxide, and also 3 to 4 titanic acid. Eger and Porsgruud in Norway. 571. + 2NaSi. Oblique prismatic; striated Fig. 507. (Sp. 570.) Fig. 508. or reed-like prisms of 86 30 to 87 45. Cl. orthodiagonal per fect, less distinct clinodiagonal, and prismatic. H. =5 5 to 6; G. =3 4 to3 5 or 3 6. Vitreous; translucent on edges, or opaque. Greenish black. B.B. fuses easily, colouring the flame yellow. Scarcely affected by aeids. C.c.: 49 silica, 31 7 iron peroxide, 6 6 iron (and manganese) protoxide, and 127 soda, with a little magnesia and potash. Has the same relation to augite as arfved- sonite to hornblende. Near Brevig and Barkevig in Norway. 572. SPODUMENE, 4A- lSi 3 + 3(i, &a, &)Si. Oblique prismatic, C 69 40. ooP 87 (fig. 509). Cl. prismatic cP and orthodiagonal, perfect; chiefly massive or foliated. H. =6 5 to 7; G. = 31 to 3 2. Translucent ; vitreous or pearly. Pale greenish grey or white to apple- green ; streak white. B.B. intumesc-es slightly, tinging the flame momentarily purplish red, and fuses easily to a colour less glass. Not affected by acids. C.c.: 65 silica, 287 alumina, and 6 &quot;3 lithia. Killiney near Dublin, Uto in Sweden, Tyrol. Killinite (sp. 651), from Killiney, seems to be decomposed spodumeue. 573. PETALITE (Castor), 4AlSi 6 + 3(ti, Na)Si 2. Oblique prismatic. Castor has C 67 34 and ooP 86 20, in irregular rect angular prisms, petalite being massive Fig. 509 (sp. 5^2). and coarse granular. Cl. basal, distinct; in a second direction