Lammerite-β, Cu3(AsO4)2, a new mineral from fumaroles of the Great Fissure Tolbachik eruption, Kamchatka Peninsula, Russia

Lammerite-β, Cu3(AsO4)2, occurs as a product of the post-eruption fumarole activity of the second cinder cone of the North breach of the Great Fissure Tolbachik eruption in 1975–1976, Kamchatka Peninsula, Russia. Sporadic light to dark green splinter-shaped grains are no larger than 0.15 mm in size. Cleavage is not observed. The mechanical admixture of finely dispersed hematite forms condensed brownish spots that are occasionally zonal relative to the contours of the lammerite-β grains. Associated minerals are euchlorine, piypite, alumoklyuchevskite, alarsite, and lammerite. Lammerite-β is brittle and transparent and has vitreous luster. The calculated density is 5.06 g/cm3. The mineral is not pleochroic, biaxial (+), α = 1.887(5), β = 1.936(5), γ = 2.01(1), 2V(calc.) = 80.9°; dispersion is strong, r < v. The new mineral is monoclinic, the space group is P21/c, a = 6.306(1), b = 8.643(1), c = 11.310(1) Å, β = 92.26(1)°, V = 615.9(1) Å3, and Z = 4. Characteristic reflections in the X-ray powder diffraction pattern (I-d-hkl) are 100-2.83-004, 10-5.65-002, and 10-4.32-020. The chemical composition is as follows, wt %: 51.30 CuO, 0.32 ZnO, 49.12 As2O3, with a total of 100.74 wt %. The empirical and idealized formulas are Cu3.00Zn0.02As1.99O8 and Cu3(AsO4)2, respectively.