New Mexico designated turquoise as the official state gem in 1967. Probably one of the oldest gemstones known, turquoise is an opaque, blue-to-green mineral. Only the prized robin's egg blue color is used to make gemstones. The majority of the world's finest-quality turquoise comes from western and southwestern United States, the largest producer of turquoise in the world.

Turquoise has been used extensively by both southwestern U.S. Native Americans and by many of the Indian tribes in Mexico since about 200 B.C. to make solid turquoise beads, carvings, and inlaid mosaics. Nearly all important deposits of turquoise are located near copper deposits in arid desert regions of the world.

Source:

Turquoise: USGS

Links:

Geological Symbols - 50 States List