December's alternate birthstone, turquoise has been mined for centuries all over the world, although the very finest examples are known to come from Iran and the Southwestern United States. Persian turquoise (also known as Sleeping Beauty turquoise) is famous for it's bright blue hues and clear, unblemished surfaces, with very little to no black or brown veining. US turquoise often displays black or brown veins which comes from limonite deposits in the turquoise's matrix. Turquoise is opaque and rates a 6 on the Moh's Scale of Hardness, so it is easy to scratch. The most traditional colors are intense blue-green, sky blue, greenish-yellow and yellowish green; the blue hues are attributed to the presence of copper, while the green and yellow hues come from additional traces of iron. The name Turquoise is thought to come from the French word for Turkish, as it was the Turks who first brought the precious gems to Europe for trade in the 16th century.
See Also: Birthstones, Moh's Scale of Hardness