Sillimanite 2

Sillimanite is the highest temperature polymorph of the aluminosilicates (Al₂SiO₅), only forming at temperatures of over 500°. It is often referred to as ‘fibrolite’, referring to the fibrous habit that is prominent in this sample. Samples of pure sillimanite are uncommon. It is usually found in association with other high temperature metamorphic minerals. This specimen also contains quartz and minor biotite.