The following information is from the 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 - 7.5
The following free streaming videos are from www.youtube.com This the normal green tourmaline
This is the chrome tourmaline. The different between the above video and this video is the shade of the green color and the price range (darker shade of green). Normally the chrome tourmaline is more expensive than the above video.
In the past, they called this one bi-color tourmaline (green and pink). The line that separate the green and pink must be in the center of the stone to acquire higher prices. In the past there were plenty of this kind of rough stones so the cutters normally cut the rough stones to have the green and pink color portions equal. This kind of gemstone is popular for making the pendant.
The following videos are the watermelon tourmaline (green color area is around the pink color). Normally the gem cutters will polish the rough stones only for this kind of gemstone. It's popular for making the pendant; unique idea creation pendant for designer.
The Paraiba tourmaline is the rare gemstone and it's expensive tourmaline.