QUARTZ FAMILY. Internally its lustre is generally splendent, sometime* passing into shining ; and is vitreous. The fracture is perfect conchoidal. The fragments are angular and sharp edged. It is most commonly semi-transparent; sometimes it approaches to translucent, but seldom to transparent. It is semi-hard in a high degree. It is brittle. It is uncommonly easily frangible. It sometimes adheres to the tongue. Specific gravity, 2.015, Klaproth. 2.144, Kir wan. 2.064, Habcrle. Chemical Characters. Before the blowpipe it is infusible without addition. Constituent Parts. Opal of Koscmutz. Of Telkobanyi Silica, 98.75 93.50 Alumina, 0.1 Oxide of iron, 0.1 1.0 Water, 5.0 98.95 99.50 According to Klaproth, t ii. p. 164. & 169. • Geognostic Situation. It occurs in primitive and floetz rocks. In primitive Country, it occurs in cotemporaneous veins along with precious opal in clay-porphyry; and in cotemporaneous plates or short beds in serpentine. In floetz rocks it oc curs in amygdaloid along with calcedony, either in vesi- cubu: