- © 2008 American Mineralogist
J.L. Jambor, A.C. Roberts, L.A. Groat, C.J. Stanley, A.J. Criddle, and M.N. Feinglos (2007) Calvertite, Cu5Ge0.5S4 , a new mineral species from Tsumeb, Namibia. Can. Mineral., 45, 1519–1523.
Calvertite was discovered during the examination of another new mineral (gallobeaudanite) from the Tsumeb mine. The un-oxidized portions of the sample in which calvertite was found consist mainly of calvertite and reinerite with minor tennantite and gallite inclusions. Calvertite occurs in a granular texture formed by a network of chalcocite veins. The calvertite grains are anhedral, elongate to elliptical with the largest grains up to 100 μm across. The calvertite postdates the reinerite as evidenced by veins of calvertite cutting reinerite. Other associated minerals in the sample are goethite, hematite, quartz, Hg-rich native silver, stolzite, otjisumerite, and various members of the alunite supergroup.
Calvertite has a metallic luster, irregular to conchoidal fracture, brittle tenacity, and no cleavage or parting. It is macroscopically black. The VHN is 283 kg/mm2 (Mohs hardness 4 to 5). It is opaque and pale bluish-gray in reflected light. No birefringence, pleochroism, or internal reflections were observed. Reflectance percentages in air are 26.3 (470 nm), 23.1 (546), 22.2 (589), and 21.5% (650).
Chemical composition was measured using an electron microprobe. Weight percent results (and ranges in parentheses) are as follows: Cu 63.10 (62.55–63.70), Fe 1.66 (1.49–1.84), Zn 0.55 (0.22–0.92), Ge 5.76 (5.58–5.98), As 1.50 (1.35–1.56), Ga 0.36 (0.31–0.39), V 0.05 (0.04–0.05), S 26.63 (26.4–26.78), corresponding to an empirical formula (based of four S atoms per formula unit) of (Cu4.782Fe0.143Zn0.041Ga0.025V0.005)∑ 4.996 (Ge0.382As0.096)∑0.478S4, Z = 1, Dcalc = 5.239 g/cm3.
The powder diffraction pattern for calvertite consists of only four lines: [d …