Violet-blue Iolite (also known as cordierite) has been called water sapphire because of its similarity to blue sapphire when cut. It can he recognized by its strong pleochroism, visible without equipment, which gives the gem its other name of dichorite. The best blue colour is seen down the length of prismatic crystals; they may appear colorless when viewed across.

Gem quality is found in alluvial deposits as small, transparent, water worn pebbles in Sri Lanka, Burma, Madagascar, and India. Other localities include Namibia and Tanzania. Crystals are found in Germany, Norway, and Finland.

A lilac to violet-blue or reddish blue variety (first found in Russia) is known as siberite.