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228 OXIDES, EABTHS, AND ACIDS. opaque. Lustre adamantine, inclining to metallic. The optic axes, seen in air through the faces b, lie in a plane parallel to c, and make angles of 17° 45' with a normal to b. Yellowish- brown, reddish-brown...hyacinth-red. Streak vellowish-white. Brittle. II = 6-0. G =4 125...4-170. Infusible before the blowpipe. Soluble in salt of phosphorus, to which it imparts a brownish-yellow colour, and in bisulphate of soda. In powder soluble, Hke rutile, in concentrated sul phuric acid. After ignition over a spirit lamp for three- quarters of an hour, its specific gravity becomes 4-192 very nearly the same as that of rutile. Ti, titanium 60"13, oxygen 39'87. Analyses of brookite a by II. Eose, b from Altan in the Ural (a = 3-81 f) by Hermann a b Titanic acid .... 89-59 94-09 Eed oxide of iron . . 1-41 4.50 Loss by ignition . . — lvll In attached crystals near Bourg d’Oisans in Dauphine with anatase, albite, quartz and crichtonite, at Tete-Noire near Chamouni in Savoy with quartz, in Steinthal near Amstag in the Canton of Uri with anatase, adularia, quartz, calcite, in tho gold stream-works of Altan between Miask and Slatoust in the Ural, combinations 6...10; Tremadoc in Caernarvonshire with quartz ; in extremely minute crystals at Biancavilla 011 Monte Calvario near vEtna. A variety of brookite in opaque black crystals implanted on quartz (arkansite) from Magnet Cove Hot Springs County, Arkansas, exhibits the combinations lcmex..v.z, differing greatly in appearance from those of tho European varieties, in consequence of the smallness of the faces b. (fig. 242.) a = 4-O80, according to Whitney, a little less than that of brookite from other localities, in conse quence probably of a slight intermixture of quartz, from which it was difficult to free it entirely. This is most likely the cause of the low density, g = 3-892...3 949, obtained by Eammels- berg. A qualitative analysis by Whitney showed it to consist of titanic acid with a trace of iron. Eammelsberg found in it at least 94 per cent, of titanic acid. The forms k, I, 0, i, n, w, h were first observed by Mr. Brooke in crystals from Snowdon, r, u, s,f,g,p were observed by v. Kokscharow in crystals from the Ural. The faces 0 are so very uneven that the symbol of the form cannot be deter mined with certainty; it may be 11 6 14. The symbol of a is probably also doubtful. *
