Preisingerite from the Yamato mine, Yamaguchi Prefecture, Japan

Abstract

Preisingerite was found in a cavity of a quartz vein from the Yamato mine, Mine City, Yamaguchi Prefecture, Japan. This is the first occurrence of preisingerite in Japan. The mineral occurs as aggregates of platy crystals up to 10 μm long in association with chlorite. The mineral is a grayish white to dark gray in color. The average of three electron microprobe analyses (WDS mode) gave the empirical formula: (Bi2.82Pb0.29)Σ3.11O1.22(OH)[(AsO4)1.57(SO4)0.13(PO4)0.11(SiO4)0.07(VO4)0.01]Σ1.89 on the basis of total cations = 5 in anhydrous part, and H2O by assuming the OH = 1. S and Si are new constituents to the preisingerite group minerals. The unit cell parameters refined from the powder X-ray diffraction data are a = 10.032 (4), b = 7.428 (2), c = 6.967 (2) Å, α = 88.03 (2), β = 114.94 (2), γ = 111.04 (2)° and Z = 2. The calculated density using the unit cell parameters and the empirical formula is 7.15 g/cm3. It is likely that preisingerite from the Yamato mine was formed by solutions containing Bi and As derived from arsenopyrite and Bi-bearing minerals such as native bismuth and joseite-A in the quartz vein.