Benleonardite, a New Mineral from the Bambolla Mine, Moctezuma, Sonora, Mexico

C. J. Stanley, A. J. Criddle and J. E. Chisholm
Department of Mineralogy, British Museum (Natural History), Cromwell Road, London SW7 5BD

Abstract: Benleonardite, ideally Ag8(Sb,As)Te2S3 with Sb > As, is a new mineral species that occurs in ore specimens collected from the dumps of the disused Bambolla mine, Moctezuma, Mexico. The associated minerals are acanthite, hessite, an unnamed Ag4TeS phase, pyrite, sphalerite, and native silver. Together with benleonardite, these form thin black crusts in fractures filled with quartz and dolomite in highly altered, tuffaceous, andesitic and rhyolitic rocks. Benleonardite is an opaque mineral and, in reflected plane-polarized light in air, it is weakly bireflectant from very pale light blue to slightly darker blue. It is not pleochroic. Luminance values (relative to the CIE illuminant C) for Ro and Re computed from visible spectrum reflectance data for the most bireflectant grain, are 33.6 and 31.7% in air, and 18.3 and 16.5% in Zeiss oil (ND 1.515) respectively. Vickers micro-indentation hardness is 105–125 (VHN25). The X-ray powder diffraction pattern could be indexed on a tetragonal cell with a 6.603(5) and c 12.726(6) Å; for Z = 2, the calculated density is 7.79 g/cm2 for the average analysis. The strongest five lines in the X-ray powder pattern are [d in Å (I) (hkl): 12.7 (70) (001); 3.188 (30) (021,004); 2.936 (100) (022); 2.608 (35) (023); 2.158 (35) (124).

Keywords: benleonardite • new mineral • Bambolla mine • Moctezuma • Mexico • reflectance data • X-ray data

Mineralogical Magazine; December 1986 v. 50; no. 358; p. 681-686; DOI: 10.1180/minmag.1986.050.358.15
© 1986, The Mineralogical Society
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