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312 ik ox. pearly, the lateral planes, when not covered with 4 roug u crust, are shining and vitreous. The principal fracture is foliated, with a fourfold c eavage the most distinct cleavage is that parallel with e terminal planes; the other three, which are pa- a e wit the lateral planes, are less distinct: the cross racture is uneven, passing into fine splintery. ternally the lustre of the principal fracture is shining n P® ar lj i the cross fracture is glimmering. It occurs in straight lamellar distinct concretions. It is translucent on the edges. It is semi-hard. Its streak is brownish-white. It is brittle. Specific gravity, 3.081. Chemical Characters. It is insoluble in water. It is soluble In muriatic acid, with exception of a small siliceous residuum. Be* tore the blowpipe, it gives out vapours of oxygenated mu- wtic acid * and is converted into a magnetic oxide of iron + © Constituent Parts. of Silica^ UI ^ a * e ^ r ° n> com kined with a small portion Gcognostie * A small piece of this mineral win «n , , aI W ' 1 "II « whole room with the sme oxygenated muriatic acid. Its niin. u. name 18 borrowed from this property. t By heating, the iron parts wi»h a nan ■. . . . 1 a part of iu oxygen to the mur “nd convert* it into oxygenated acid.