238 QUARTZ FAMILY* Third Subspecies. Fire Opal. Feur Opal, Karsten, ' Feur Opal, Karsten $ Klaproth, Beit. iv. s. 156. Karsten, Tabcl. p. 26. Id. Steffens, b. i. s. 138. Id. Lenz, b. i. s. 402. Id' Oken, b. i. s. 275. External Characters. Its principal colour is hyacinth-red, which passes through honey-yellow into wine-yellow; and upon light er places shews a carmine-red and apple-green iridescence. In its interior, dendritic delineations are sometimes to be observed. Internally it is splendent, and the lustre is vitreous. The fracture is perfect conchoidal. , The fragments are angular and sharp edged, or tabu lar. It occurs in distinct concretions, which are partly thick and curved lamellar, partly large and coarse granular. It is completely transparent. It is hard. Uncommonly easily frangible. Specific gravity, 2.120, Klaproth, Chemical Characters. When exposed to heat, its colour changes into p n ^ e flesh-red; it becomes translucent, and traversed with nu merous fissures. Constituc* 1