Sillimanite is an aluminum silicate mineral, shown here by the White Sillimanite photograph from our August 2024 collection.
Mineral background
Its chemical formula is Al2SiO5. It shares that composition with kyanite and andalusite, while having a different crystal structure. Sillimanite commonly occurs in rocks formed under high-grade metamorphic conditions and can grow as prismatic crystals or fibrous aggregates.
Appearance
White and colorless material are among its natural colors; other examples may be gray, brown, yellow, green or blue. The photograph is a collection record, with no specimen-specific laboratory report attached.
