Turquoise is a naturally occurring copper-aluminum phosphate mineral, prized for thousands of years for its sky-blue to green color. It forms in arid regions where mineral-rich water seeps through rock, and the brown or black veining many stones carry, called matrix, is the surrounding host rock left within the gem.
The color comes from the metals locked in the stone. Copper drives turquoise toward sky-blue and robin's-egg blue, while iron pulls it toward green; most stones fall somewhere along that blue-to-green spectrum. Hardness varies just as widely, from chalky, porous material to dense, glassy stone that takes a high polish.
Matrix is the veining or webbing of host rock left within the gem — limonite browns, black manganese, golden pyrite. Far from a flaw, matrix is often what collectors prize: a tight, even “spiderweb” pattern can make a stone more desirable, and the matrix is one of the clues that helps identify which mine a stone came from.
Turquoise forms slowly in dry, copper-rich ground where water carries minerals through fractured rock over millions of years. That geology explains its geography: the great deposits cluster in arid regions — the American Southwest, northern Mexico, Iran, China, and Central Asia — and each mine yields stone with a recognizable color and matrix signature.
In the Southwest, turquoise has been worked for well over a thousand years and remains sacred to many Native nations, valued long before it was ever set in silver. The pairing of turquoise and sterling that defines Navajo, Zuni, and Hopi jewelry dates only to the later nineteenth century, but the stone's standing is far older.
Because natural high-grade turquoise is rare, most turquoise on the market is treated — commonly stabilized with resin to harden it for cutting. Treatment is legitimate and widely accepted; what matters is disclosure. A trustworthy seller names the stone's mine where it is known, states its treatment, and stands behind both.