Abstract

Billingsleyite is a new silver sulfosalt from the North Lily mine, East Tintic district, Utah. It is associated with argentite, tennantite, bismuthinite, galena and pyrite. Analysis gave Ag 75.59, Cu 0.02, Fe 0.06, As 5.73, Sb 1.50, S 16.28, insol. 0.61, total 99.79, corresponding to Ag7(As0.86Sb0.14S6. The mineral occurs as fine-grained aggregates with a dark lead-gray color and metallic luster; slightly sectile. H =½. Billingsleyite is isostructural with synthetic Ag7SbS6 (space group C2221; a= 14.96 Å, b=14.99, c= 10.56; density = 6.00) and synthetic Ag7AsS6 (ab∼14.82 Å c= 10.48; density = 5.90). A complete series extends between these end-components; synthetic Ag7(As0.5Sb0.6)S6 has ab∼14.88 Å, c= 10.53; density 5.96. The natural material has ab∼14.8 Å, c=10.4; density = 5.92±0.02 (meas.). Indexed X-ray powder diffraction data are cited. In addition to the syntheses by the writers, both end-compositions have been synthesized by Gaudin and McGlashin (1938) and Hall (1965), and Ag7AsS6 by Roland (1965). The name is given after Paul Billingsley (1887-1962), mining geologist who discovered the North Lily mine and in 1930 collected the only known specimens.

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