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MIYACOLITE. 369 mixture of nearly equal parts of carbonate of lime and silicate of alumina and red oxide of iron. 209. RHYACOLITE.—Empyrodoxer Peld-Spatb; Mohs. Ryacolith; Hausmann, Haidinger. Oblique. 101,100=65° 37''3; 111,010 = 63° 19'; 101,001 = 50° 28'-6, a loo twin-face, b 010, c ooi, n 021, x 101, y 201, o 111. be 90° o' ob 63° 19' ab 90 0 yo 39 19 ca 116 6 on 43 56 xc 50 29 mo 66 68 yc 80 28 oc 56 21 ym 45 26 cm' 67 41 nb 45 16 xm 69 8 zb 29 41 xbm 65 37 mb 69 41 ybm 35 37 FIG. 384. \ z' \ b z b Combinations, oxcmb, xcnymb, oxcnymzb. Twin crystals, l- Twin-face a. 2. Twin-face n. co = 89° 28'. Cleavage. c , perfect; b, less perfect, yet distinct. Eracture conchoidal. transparent...translucent. Lustre vitreous. Colourless, white, greyish, yellowish. Streak white. Very brittle, u = 6 0. G = 2-67...2-62. Before the blowpipe is rather more fusible than felspar, and imparts a yellow colour to the flame. Is decomposed by hy drochloric acid leaving a residue of silica in powder. RSi + AlSi J , where R is soda, potash and lime. Analysis by G. Rose:— Silica .... Alumina ... Red oxide of iron . . . 0'28 Lime .... Magnesia . . . . . . 023 Potash .... . . . 6-92 Soda . . . 10'56 Is found in small transparent crystals in volcanic matter at the foot of Vesuvius, in imbedded crystals in the lavas of the Biftel, and at the lake of Laach.
