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November/December 2008

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Connoisseur's Choice: Kyanite, Minas Gerais, Brazil



One of the most interesting and at times quite beautiful rock-forming minerals is kyanite. It is one of a triad of aluminosilicates that often develop during regional metamorphism, each within its own well-defined temperature and pressure fields; the remaining two members, sillimanite and andalusite, are also familiar to many collectors. Although common in most belts of regionally metamorphosed rocks and described from many hundreds of localities, kyanite is particularly well known as a valuable industrial mineral from a far smaller number of sites where it is mined for the production of refractory materials or from sites where it is collected for unusual mineral specimens and gems. It is especially familiar to collectors because the kyanite-rich “quartzite” once exploited at Graves Mountain, Georgia, is also host for some of the world’s finest rutile and lazulite specimens (Cook 1985, 2008). Surprisingly attractive, reasonably priced kyanite specimens are traditionally available from several Brazilian localities at most mineral shows, and one such specimen has been suggested for this issue’s Connoisseur’s Choice.
Dr. Robert B. Cook, an executive editor of Rocks & Minerals, is a professor emeritus in the Department of Geology and Geography at Auburn University, Auburn, Alabama.


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