Andalusite

Andalusite, together with kyanite and sillimanite, are polymorphs of aluminium silicate. It has an orthorhombic crystal structure, and the crystal form is columnar with a nearly square cross-section. Black carbon inclusions are sometimes located at the four corners or at the centres of the crystals, arranged like a regular cross, which is called chiastolite. The aggregates are radial, like a chrysanthemum flower, so it is also locally called the ‘chrysanthemum flower stone’. It is pink, light red, light brown, light white, light grey or light green in colour. It has transparent to opaque diaphaneity, a vitreous lustre, a specific gravity of 3.13–3.16, a Mohs hardness of 6.5–7.5 and uneven to conchoidal fractures. Andalusite is mainly a product of contact metamorphism and is commonly found in the contact zone between intrusive rocks and argillaceous rocks. It can sometimes be found in crystalline schist. It often forms together with kyanite, cordierite, sillimanite and corundum....