Tourmaline

History
Tourmaline has been around for hundreds of years, and have been mistaken for several other more expensive gemstones, from emerald to ruby. First mined in Sri Lanka, the name tourmaline comes from the word "turmali" meaning common stone, as tourmalines were abundant. Many of the gemstones in some 17th century Russian crowns are tourmalines.

Features
Occurring in a variety of colors from colorless to black, tourmalines generally form in long thin crystals, occasionally changing color two or more times in the same crystal. Tourmaline frequently occurs inclusion free, but it may also contain fine tubular inclusions which can cause a cat's eye effect. Tourmaline shows a difference in color depending on how the stone is viewed. When viewed down the length of a crystal, a tourmaline may appear much darker in color, sometimes black, while the best color is seen when the stone is viewed at right angles to its length.

Treatments
Dark green tourmaline is sometimes heat treated to produce a brighter more pleasing emerald green color. Other colors are generally not heat treated, as heating tends to lighten the existing color.

Principal Deposits
The Ural Mountains in Russia produce some fine tourmaline crystals, as do mines in Sri Lanka, Brazil, Tanzania and Kenya. The United States produces some of the world's finest blue tourmaline, known as indicolite.

Rarity 
It is fairly common to find good color green tourmalines of decent size and excellent clarity. Colorless tourmaline, fine blue tourmaline, and good quality bi-color tourmaline are more difficult to find. Cat's eye tourmaline over a carat in size is also difficult to obtain.