Namibite and hechtsbergite from the Nagatare mine, Fukuoka Prefecture, Japan

Abstract

Namibite [Cu(BiO)₂VO₄(OH)] and hechtsbergite [Bi₂O(VO₄)(OH)] were found with clinobisvanite, waylandite, eulytite, beyerite and bismutite at the Nagatare mine, Fukuoka Prefecture, Japan. This assemblage occurs as secondary minerals and forms crusts and euhedral crystals associated with lepidolite, quartz, albite and cookeite. Namibite forms a dark green powder with pearly luster. Hechtsbergite is yellow, and is found as fine isolated crystals or aggregates. The compositions of namibite and hechtsbergite, determined by electron microprobe, are Cu_0.98Bi_1.92Al_0.04O₂ (V_0.96Si_0.07P_0.02)O₄ (OH) and Bi_1.94Al_0.01O(V_1.00Si_0.04)O₄ (OH), respectively. The unit-cell parameters are a = 6.216(4), b = 7.384(6), c = 7.467(6) Å, α = 90.19(8), β = 108.65(7), γ = 107.36(8)°, V = 308.1(3) ų for namibite, and a = 6.954(5), b = 7.539(8), c = 10.870(9) Å, β = 106.87(5)°, V = 545.4(6) ų for hechtsbergite.