Tourmaline

Tourmaline is the most colour-variable gemstone there is. A single crystal can run from green at one end to pink at the other, and no two stones are alike.

Sri Lankan material is mostly green and pink, often with excellent clarity. Tourmaline is a 7 to 7.5 on the Mohs scale and is untreated — the colour you buy is the colour it came out of the ground.