The following information is from website: http://en.wikipedia.org/wiki/Tourmaline
Tourmaline is a crystalsilicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors. The name comes from the Sinhalese word "turamali" (ටුරමලි) or "toramalli" (ටොරමල්ලි), which applied to different gemstones found in Sri Lanka.
The hardness (Mohs scale) : 7.0 - 7.5
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