Beautiful blue/green turquoise is the designated birthstone for the month of December (with zircon and tanzanite). It is also the gemstone for the 11th wedding anniversary.
The word turquoise dates to the 17th century and is derived from the French meaning "Turkish" because the mineral was first brought to Europe through Turkey.
The finest of turquoise reaches a maximum MOHS rating of just under 6, or slightly more than window glass.
Turquoise is formed when water enters an iron-rich limonite or sandstone that contains copper, aluminum and other minerals. It takes millions of years and the right conditions for turquoise to be formed. The gemstone’s blue color can be attributed to the presence of copper while the presence of aluminum adds a greenish hue to the gem.
Turquoise may contain narrow vein-like markings of its host rock. These markings are known as the matrix. Limonite creates a dark brown marking while sandstone creates tan markings.