Sillimanite, also called Fibrolite, is a colorless, or white glassy silicate mineral frequently found infibrous aggregates. It occurs in high-temperature regionally metamorphosed clay-rich rocks. It occurs with andalusite, kyanite, potassium feldspar, almandine, cordierite, biotite and quartz in schist, gneiss, hornfels and also rarely in pegmatites. It is an index mineral indicating high temperature but variable pressure. Sillimanite is used in the manufacture of high alumina refractories or 55-60% alumina bricks.
