The mineral kyanite is an aluminium silicate of the sillimanite group (along with andalusite and sillimanite), also called alumino-silicate. It has the formula Al2O3Â·SiO2 (Al2SiO5). Its hardness varies widely depending on its crystallographic direction, from 5 to 7.5, and it has a specific gravity of 3.56-3.67.
It is translucent, usually blue, but possibly white, gray, green, or black. It is usually found in long-bladed crystals or columnar to fibrous structures.
Kyanite is used in refractory and ceramic products. Noted deposits are found in Brazil, USA (North Carolina, Virginia, and Georgia), Switzerland, Russia, India and Kenya. Kyanite is found in such metamorphic rocks as gneiss and schist. The name “kyanite” is derived from the Greek word for “blue.” It was originally named “Cyanite” for its (common, but not overall) blue hue. This name was later changed because kyanite doesn’t only appear blue (green and black are common too).