cordierite

A Dictionary of Earth Sciences | 1999 | 659 words | Copyright

cordierite Silicate mineral Al₃(Mg,Fe)₂[Si₅AlO₁₈] which can be iron-rich and is a member of the cyclosilicate group; sp. gr. 2.5–2.8; hardness 7; orthorhombic; dark blue or greyish-blue, translucent to transparent; vitreous lustre; crystals rare, prismatic or pseudo-hexagonal, but usually occurs massive; cleavage imperfect metamorphism, parting cyclosilicate; occurs in aluminous rocks that have been subjected to thermal or regional metamorphism, in hornfels, schists, and gneisses, in association with andalusite, spinel, quartz, and biotite. Fine dark blue examples are used as gemstones. It is named after the 19th-century French geologist P. L. A. Cordier.

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AILSA ALLABY and MICHAEL ALLABY. "cordierite." A Dictionary of Earth Sciences. 1999. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-cordierite.html