What Is Turquoise? A Porous Stone That's Almost Always Treated

Turquoise is a hydrated phosphate mineral containing copper and aluminum. Its signature blue comes from copper content; a greener tone usually means more iron or a higher water content in the specimen. It forms where copper deposits weather in arid climates, which is why classic sources — Iran, the American Southwest, and parts of China — all share dry desert environments.

Untreated turquoise is soft (around 5–6 on the Mohs scale) and porous enough to absorb oils and change color with wear. Because of this, the vast majority of turquoise sold today — including in fine jewelry — is stabilized: treated with a clear resin under pressure to fill its natural pores, harden the surface, and lock in its color. This is standard practice, not a sign of low quality, but genuinely untreated turquoise is rare and typically sold at a premium.