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A steel-gray mineral, chiefly Bi2Te2S.

[German Tetradymit, from Late Greek tetradumos, fourfold (from the double twin crystals in which it usually is found) : Greek tetra-, tetra- + didumos, double; see dwo- in Indo-European roots.]
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 grey metallic mineral consisting of a telluride and sulphide of bismuth. Formula: Bi2Te2S
[C19: from Late Greek tetradumos fourfold, from Greek tetra- + didumos double]
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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Devouard performed EDX-analyses of a few of these associated minerals and found significant amounts of tellurium; this possibly is attributable to primary bismuth tellurides such as tetradymite or tsumoite having once been present in this gold-rich ore.
Tetradymite was described by Turneaure (1935) as inclusions in bismuthinite from the Contacto vein, Level 446.
Empirical formula: [([Bi.sub.2.92][Pb.sub.0.02]).sub.[SIGMA]2.94] [Te.sub.1.01][([Se.sub.1.75][S.sub.0.32]).sub.[SIGMA]2.07]* Relationship to other species: It is related to the members of the tetradymite group.