andalusite science definition

A hard, grayish white to pinkish brown orthorhombic mineral. Andalusite occurs as nearly square prisms, often with cross-shaped cross sections, in metamorphic rocks. It is a polymorph of kyanite and sillimanite, but forms at shallower depths than they do, and at higher temperatures than kyanite and lower temperatures than sillimanite. Chemical formula: Al₂SiO₅.