Chemistry and crystallography of Bi-rich izoklakeite from the Otome mine, Yamanashi Prefecture, Japan and discussion of the izoklakeite-giessenite series

Abstract

Giessenite was reported as an acicular crystal that shared a close association with Sb-bearing cosalite from the Otome mine, Yamanashi Prefecture (Ozawa and Hori, 1982). Recent criteria classify it as izoklakeite.
The Otome izoklakeite, which is orthorhombic (Pnnm or Pnn2 from its orthogonal lattice and systematic extinction, in agreement with previous reports), has unit-cell dimensions of a 34.067, b 38.085, c 4.056Å. In addition, diffuse reflections which double the periodicity of 4.056Å along the c-axis are observed, also in agreement with the report on Vena izoklakeite (Zakrzewski and Makovicky, 1986).
An electron microprobe analysis gives Cu 0.8, Fe 0.3, Ag 1.1, Pb 46.5, Bi 27.2, Sb 7.3, S 16.2, total 99.4wt.%, yielding the empirical formula (Cu_2.7Fe_1.2)_3.9Ag_2.2Pb_48.7(Bi_28.2Sb_13.0)_41.2S_109.7, assuming the total cation=96 in a unit cell. It has a Sb/(Sb+Bi) value of 0.316, and is the most Bi-rich of the known izoklakeites.