Turquoise is a mineral species formed of phosphate hydrate of copper and aluminum whose chemical composition is CuAl6(PO4)4(OH)8·4H2O.
Its name would come from “Turkish stone”, since it was more particularly known in Europe at the time of the Crusades. She gave her name to the turquoise color, a shade of blue. The Iranians call it “firouze”. The Turks have taken over the same name, the ore coming from Iran. Having received it from Turkey, the Europeans call it “turquoise”.
Stone of blue color, not transparent (semi-opaque), sometimes translucent on the edges. Variety of phosphate of alumina, called old rock, very sought after especially blue. Easily recognizable by its celestial blue color, sometimes greenish. Infusible with the blowpipe, dissolves in acids without effervescence, without residue, offering copper colorations. It sometimes happens that the turquoises pass from the brilliant blue to the dull blue: they are said to have died or been extinct.
Yellow Turquoise, from China