Minerals (Category B)
Staurolite is a mineral that is commonly found in metamorphic rocks such as schist and gneiss. It forms when shale is strongly altered by regional metamorphism. It is often found in association with almandine garnet, muscovite and kyanite - minerals that form under similar temperature and pressure conditions.Staurolite is a silicate mineral with a generalized chemical composition of (Fe,Mg)2Al9Si4O23(OH). It is usually brown or black in color with a resinous to vitreous luster. It ranges from transparent to opaque in diaphaneity.
Staurolite is usually easy to identify when it occurs as visible grains in a metamorphic rock. Grains of staurolite are typically larger than the grains of other minerals in the rock and they often exhibit an obvious crystal structure. They occur as six-sided crystals, often with penetration twins.