Andalusite is an aluminium nesosilicate mineral. Andalusite is trimorphic with kyanite and sillimanite, being the lower pressure mid temperature polymorph. At higher temperatures and pressures, andalusite may convert to sillimanite. Thus, as with its other polymorphs, andalusite is an aluminosilicate index mineral, providing clues to depth and pressures involved in producing the host rock. The variety chiastolite commonly contains dark inclusions of carbon or clay which form a cruciform pattern when shown in cross-section. A clear variety first found in Andalusia, Spain can be cut into a gemstone. 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. It is associated with mica schist which increases alkali content in ultimate product and so it has not been exploited economically so far. Andalusite is an aluminium compound with high heat resistance used in furnaces, kilns and other industrial processes. South Africa possesses by far the largest portion of the world`s known andalusite deposits.

圖片編號： 131681586
拍攝者： Mohaeljawphoto