Tourmaline
The tourmaline group refers to a number of related species and varieties of minerals. Tourmaline is a complex crystalline silicate containing aluminum, boron, and other elements, and is used in electronic instrumentation and, especially as a gemstone in its green, clear, and blue varieties.
Although tourmaline has been known since ancient times, it was only imported by the Dutch from Sri Lanka in 1703. The name "tourmaline" is derived from a Sinhalese name, "turamali," meaning "stone with mixed colors."
Chemical Group: Silicate ♦ Group: Tourmaline ♦ Crystal forms: Trigonal system ♦ Color: black, brown, dark blue, colorless, pink, red, green, blue and even multicolored. Crystals frequently contain two or more colors ♦ Luster: Vitreous ♦ Transparency: Transparent to opaque ♦ Fracture: Conchoidal ♦ Cleavage: Poor ♦ Moh's hardness: 7.5 ♦ Localities: Brazil; The USA from Maine, New Hampshire, South Dakota, California.