Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5.

The variety chiastolite commonly contains dark inclusions of carbon or clay which form an X or a cross in section.

A clear variety first found in Andalusia, Spain can be cut into an interesting gemstone.[2] Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of iridescence, although the colors are actually the result of unusually strong pleochroism.