One of the oldest known gemstones, turquoise was mined by ancient populations prior to 4,000 B.C.  The bluish green gemstone was used as an ornament in ceremonial dress by Egyptian pharaohs and early Native Americans.  The most valuable turquoise deposits are in Neyshabur, Iran, but mines also exist across Africa, Australia, and the Southwestern U.S. Turquoise is the anniversary gemstone for the fifth year of marriage.