Cervelleite, Ag (sub 4) TeS, a new mineral from the Bambolla Mine, Mexico, and a description of a photo-chemical reaction involving cervelleite, acanthite and hessite

Cervelleite occurs as thin 30 mu m rims surrounding acanthite in hessite and as vermiform inclusions in the latter, associated with native silver, benleonardite, pyrite and sphalerite, with dolomite and quartz as fracture fillings in highly altered silicified rhyolite on the spoil tips of the abandoned Bombolla mine, Moctezuma, Sonora, Mexico. It is isotropic and opaque; in plane-polarized light it is slightly bluish to slightly greenish white; VHN (sub 10) 26; reflectance spectra are reported. Microprobe analyses gave Ag 73.0, Cu 0.1, Te 22.2, S 5.3 = 100.6, leading to the idealized formula Ag (sub 4) TeS. Indexed XRD powder data are tabulated; strongest lines 5.00 (vvs), 4.24 (vs), 6.29 (s), 3.766 (ms), 4.64 (m) A; a 14.03 A; Z = 24 giving D (calc.) 8.53 g/cm (super 3) . Cervelleite, acanthite and hessite are altered rapidly and profoundly by light; a surface reaction of photo-chemical origin is deduced. The name is for Dr B. Cervelle (1940-) of Paris, currently Chairman of the Commission on Ore mineralogy of the IMA.