gems, turquoise, Iran, Persia, Nishapur

Bouillon-LaGrange reviews the long-standing confusion between true Persian turquoise and the European material then commonly called turquoise, which was frequently interpreted as fossil bone or teeth colored by copper or iron. He summarizes earlier observations on Persian deposits near Nishapur, distinguishing the celebrated “Old Rock” from inferior “New Rock” material, and discusses competing mineralogical classifications. His chemical investigation concerns specimens resembling the so-called occidental turquoise. He records a specific gravity of 3.127, light green to blue color, sufficient hardness to scratch glass slightly, loss of color on heating, and solubility in nitric and muriatic acids. Analysis indicated that the material consisted predominantly of phosphate of lime, accompanied by carbonate of lime, phosphates of iron and magnesia, alumina, water, and traces of manganese, with no detectable copper. Experiments by Vauquelin likewise failed to detect copper. Bouillon-LaGrange therefore attributes the greenish-blue color to iron phosphate and demonstrates experimentally that iron compounds can produce colors resembling those associated with copper. The study is historically important for showing that substances then grouped under “turquoise” could be chemically distinct, although the material analyzed was evidently not true mineral turquoise. The article was published in Annales de Chimie, Vol. 59, No. 2, pp. 180–195, (1806); the Philosophical Magazine, Vol. 26, pp. 220–229, (1807); and the Journal für Chemie, Physik und Mineralogie, Vol. 3, No. 1, pp. 88–97, (1807).