Kyanite is very anisotropic, meaning it has a different hardness depending on the angle. Its vertical hardness ranges from 4.5 to 5.5, while the horizontal hardness is from 6 to 7 on the Mohs scale. This characteristic of the mineral led to it being commonly called “disthene”, meaning two strengths.

Kyanite is named from the Greek term cyanos, meaning deep blue.