Kyanite

Kyanite, aluminium silicate, formula Al₂SiO₅.

Crystal system: Triclinic (crystals common, usually tabular, elongated blades).
Hardness: Varies, 4 to 4.5 along the planes; 6 to 7 perpendicular to the planes.
Density: 3.6 to 3.7
Colour: White, yellow, grey, green or blue.
Streak: White.

Kyanite is a common mineral found in aluminium-rich metamorphic rocks. It is used in the manufacture of fire-proof and acid proof materials such as porcelain and sparking plugs. Clear crystals are used as precious stones. Fine mineral specimens are found at St. Gotthard in Switzerland and several locations in Brazil.

The specimen shown came from Barra de salinas, Minas Gerais, Brazil.