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 (do͞o-môr′tē-ə-rīt′, dyo͞o-)
A glassy pink, green, violet, or blue aluminum borosilicate mineral, Al8BSi3O19OH, used in spark-plug ceramics and as imitation lapis lazuli.

[French, after Eugène Dumortier, 19th-century French paleontologist.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Minerals) a hard fibrous blue or green mineral consisting of hydrated aluminium borosilicate. Formula: Al7O3BO3(SiO4)3
[C19: named after Eugène Dumortier, 19th-century French palaeontologist who discovered it]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
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Tucson 2015: exceptional colored stones and gem artistry, Brazilian Cu-bearing tourmaline and emerald, Oregon sunstone and pearl market updates * Conference reports * Amblygonitemontebrasite carving * Moroccan amethyst * Dumortierite in quartz * Jadeite with high albite content * Moldavite imitation * Iridescent scapolite * Composite quartz beads * CVD synthetic diamond with unstable color * The Foldscope.
The Ambatofinandrahana region is most famous for quartz with and without inclusions, epitactic hematite on rutile, bastnasite, tourmaline and beryl, including huge crystals of aquamarine, with dumortierite crystals, encased in solid pegmatite.
(Saul subsequently discovered the ruby deposits in the Tsavo West area of Kenya--at what became the famous John Saul Ruby mine.) Saul bought some of de Souza's crystals, at that time labeled as dumortierite, and sent them to a number of people for a proper identification.
Dumortierite [Al.sub.7](B[O.sub.3])(Si[O.sub.4])[O.sub.3]
Associated minerals are: alkali-feldspar, plagioclase, quartz, sekaninaite, andalusite, topaz, garnet, biotite, muscovite, dumortierite, schorl, zircon, apatite, monazite, ilmenite, pyrite, cordierite, sericite and chlorite.