Kyanite

Kyanite, whose name derives from the Greek word "kuanos", meaning deep blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. With Kyanite, most stones exhibit areas of light to dark colour zones, along with white streaks. Kyanite specimens have a variable hardness. The long crystals have a Mohs hardness of about 4.5 to 5 if tested parallel to the length of a crystal, and a hardness of 6.5 to 7 if tested across the short dimension of a crystal.