What is Iolite?
Iolite is a blue gem notable for its strong trichroism which has such a pronounced contrast it can often be clearly seen by eye when simply turning the stone in your fingers. Iolite is actually a variety of the mineral species cordierite, but the iolite name was derived from the Greek word “Ios' for violet and the stone was often referred to as 'water sapphire' because its strong pleochroism results in stones looking like sapphire in one direction but much clearer from the other side.
Iolite under the dichroscope
Under a dichroscope, iolite can show three pleochroic colours. Even the body colour of a gemstone or gem material can alter dramatically just by turning in the hand, the colours seen being yellow, blue and violet.