Turquoise

Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium. It is rare and valuable in finer grades and has been prized as a gemstone and ornamental stone for thousands of years owing to its unique hue. The substance has been known by many names, but the word turquoise dates to the 17th century and is derived from the French 'turquois' meaning 'Turkish' because the mineral was first brought to Europe through Turkey, from mines in the historical Khorasan of Persia.

Formation & Geology

Turquoise forms by the action of percolating acidic groundwater on copper-rich rocks. It requires a dry (arid) climate to form. It is typically found in arid regions, filling cavities and fractures in altered volcanic rocks. The blue color comes from copper, while green tones are caused by iron impurities.

Physical Characteristics

Turquoise is cryptocrystalline, meaning its crystals are too small to be seen. It is almost always opaque. Its hardness varies; high-quality material is hard (up to 6), while chalky material is softer and more porous. It often contains dark veins of the host rock (matrix).

Historical Significance

Turquoise is one of the first gems ever to be mined. Ancient Egyptians mined it in the Sinai Peninsula as early as 6000 BC. It was a holy stone to native tribes of the American Southwest and to the Aztecs, who used it in ceremonial masks. It is the birthstone for December.

Treatments & Stabilization

Because natural turquoise is often porous and chalky, over 90% of the turquoise on the market is "stabilized." This involves impregnating the stone with a clear epoxy resin to harden it and lock in the color. This is an accepted industry practice. "Reconstituted" or "block" turquoise is dust mixed with glue and dye, which is considered an imitation.