andalusite

Updated About encyclopedia.com content Print Article Share Article
views updated

andalusite (chiastolite) A member of the Al2SiO5 (or Al2O3.SiO2) group of polymorphic minerals; the other members of this group are kyanite and sillimanite. The mineral mullite (3Al2O3.2SiO2) is related to this group of minerals; sp. gr. 3.2; hardness 6.5–7.5; orthorhombic; pink or red, sometimes grey-brown and green, transparent varieties used as gemstones; vitreous lustre; crystals prismatic with a pseudo-tetragonal form which has a characteristic cross-section, can also be massive; cleavage at right angles, distinct {110}; occurs principally in thermally metamorphosed rocks that show alteration to aggregates of white mica, in low-grade, regionally metamorphosed rocks, and also in granites and pegmatites together with corundum, tourmaline, topaz, and other minerals. The name is derived from Andalusia in Spain.

More From Encyclopedia.com


You Might Also Like