Tsumebite from the Kisamori mine, Akita Prefecture, Japan

Tsumebite was discovered in a dump at the Kisamori mine, Daisen City, Akita Prefecture, northeast Japan. The mineral occurs as nodular aggregates (up to 0.5 mm in diameter) of platy crystals, up to 0.1 mm in length and 0.02 mm in thickness, in association with pyromorphite, quartz, limonite, and a clay mineral (potassic aluminum silicate). It is emerald green in color with a vitreous luster. The unit cell parameters obtained from the powder X-ray diffraction data are a = 7.850(2), b = 5.797(1), c = 8.712(2) Å, β = 111.92(2)°, V = 367.8(1) Å3, and Z = 2. Electron microprobe analyses indicate the empirical formula Pb2.02(Cu0.99Al0.01Zn0.01)Σ1.01(PO4)1.01(SO4)0.96(OH)1.12 on the basis of total cations = 5 atoms per formula unit in the anhydrous part and the amount of OH calculated from a charge balance. The calculated density is 6.23 g/cm3. It is likely that the present tsumebite was formed from a solution containing Pb, Cu, PO4, and SO4 ions after crystallization of pyromorphite.