Turquoise is a hydrous copper aluminum phosphate found as vein fillings and nodular masses in arid volcanic rock, typically in desert climates where weathering concentrates copper. The best specimens show a strong sky-blue hue; greenish material reflects higher iron content. It takes a fine waxy polish despite being relatively soft, which is part of its appeal to lapidary artists. The bad news for collectors: dyed howlite, dyed magnesite, and synthetic imitations are so common at markets that untreated natural turquoise commands a premium. A 10x loupe revealing characteristic pale spiderweb matrix and slight surface irregularities helps separate natural from treated material.
The copper connection
Turquoise is the third member of the association's copper suite: a hydrated copper-aluminum phosphate that forms in the same oxidized zones that produce azurite and malachite, which is why the three so often share a locality list. Unlike its carbonate cousins it does not effervesce in acid — a quick drop test separates a pale turquoise from any blue-green carbonate crust.