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2 58 QUARTZ FAMILY. and red. Of grey, it presents the following varieties, smoke, bluish, yellowish, and pearl grey ; from pearl- grey it passes into lilac-blue and lavender-blue; also into brick-red, which inclines to yellow; from yellowish-grey it passes into straw-yellow, and ochre-yellow ; from smoke-grey into greyish-black, and ash-grey. It generally exhibits but one colour, and is sometimes marked with dotted, flamed, striped, and clouded delinea tions. The grey varieties are generally brick-red in the rifts. It often presents brick-red vegetable impressions; and this is most frequently the case with the lavender-blue varieties. It occurs most commonly massive, and in angular pieces; and is frequently cracked in all directions. Internally it is glistening, sometimes approaching to shining, sometimes to glimmering, and even to dull; and the lustre is vitreo-resinous. The fracture is imperfect conchoidal, and sometimes large and flat, and occasionally small conchoidal. The fragments are angular and sharp edged. It is opaque. Hard in a low degree. Easily frangible. Rather heavy in a low degree. Specific gravity, 2.330, Kirw. 2.430, Karst. 2.431, 2.432, 2.461, 2.577, 2.595, 2.646, Hoff. Chemical Characters. The lavender-blue variety, when exposed to a heat of 151° of Wedgwood, according to Kirwan, melts into a spongy yellowish-grey semi-transparent mass. Other varieties,
