TURQUOISE, is the tooth of an animal penetrated with the blue exhalation of copper: it loses its colour when heated;
Turretin it is opaque, and of a lamellar texture, and susceptible of a fine polish; its specific gravity is from 2.5 to 2.928; some are of a deep blue, some of a whitish blue, but become of a deeper when heated. This substance is found in Persia and Languedoc. The copper may be extracted from it by distilled vinegar. According to Reaumur (Mem. Par. 1715) nitrous acid will not dissolve that of Persia, though it will that of France, which shows a difference between them.