The colour normally associated with iolite is blue, and its name comes from the Greek word meaning violet. Iolite also has other colours, which we will explain under the next section pleochroism.

Pleochroism

The differential selective absorption of the ordinary ray and the extraordinary ray in uniaxial stones (dichroism), or of the three rays corresponding to the three principal vibration directions in biaxial stones (trichroism). Iolite is very strongly pleochroichic. The three colours for the three axes are pale blue, dark violet blue, and yellow. This means that it is important for iolite to be cut in the correct direction relative to its axes.