Tourmaline

 Color: Colorless, Pink, red, yellow, brown, green, blue, violet, black, multicolored
Color of streak: White
Mohs' hardness: 7-71/2
Density: 2.82-3.32

The Tourmaline group refers to a number of related to number of related species and varieties. Even through tourmaline has been known since antiquity in the Mediterranean region, the dutch imported it only in 1703 from Sri Lanka to Western and Central Europe.

According to color, the following varieties are recognized by the traders: 

Achrolite, Dravite, Indicolite, Rubilitte, Schorl, Seberite, Verdelite, Beruergerite, Dravite, Elbaite, Liddicoatite, Schorl, Tsilaisite, Uvite. 

Tourmaline is considered to be the 8th Anniversary gemstone. It is categorized as a semi-precious stone. It comes in various shades and hues; the most common among them is the multi-coloured tourmaline. As the name suggests, it is a stone that has two or more different colours and are sometimes referred to as either 'rainbow tourmaline' or even bi-coloured tourmaline. It is considered to be one of the most complicated minerals put together with mixed crystals of aluminium boron silicate. One can create completely different shades with the slightest changes in the composition. The name 'Tourmaline' is derived from a Singhalese word "Thuramali" or "Thoramalli" a term given to distinct gemstones in Sri Lanka.