Starovaite, KCu5O(VO4)3, a new mineral from fumarole sublimates of the Tolbachik volcano, Kamchatka, Russia

Abstract

The new mineral species starovaite, ideally KCu 5 O(VO 4 )3, has been found in the sublimates of the Yadovitaya fumarole at the Second scoria cone of the Northern Breach of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. The mineral is associated with lammerite, hematite, palmierite, tenorite, piypite, rutile, orthoclase, lyonsite, pseudolyonsite, lammerite-β, langbeinite, calciolangbeinite, and cupromolybdite. Starovaite occurs as prismatic crystals up to 3 × 6 × 20 μm or divergent long-prismatic crystals up to 1 × 3 × 70 μm. The crystals are combined in sprays, sheaf-like aggregates or crusts up to 0.3 × 0.5 mm overgrowing lammerite. Starovaite is golden brown to reddish brown with a semi-metallic luster. The mineral is brittle, VHN is 182 (range 165–195) kg mm −2 . Cleavage and parting were not observed, fracture is uneven. D (calc.) = 4.54 g cm −3 . In reflected light, starovaite is grey with a brownish hue. Bireflectance is weak, internal reflections are distinct red-brown, anisotropy is weak. The reflectance values [ R 1 −R 2 , % (λ, nm)] are: 14.2–12.45 (470), 13.2–11.6 (546), 13.0–11.4 (589), 12.6–11.35 (650). The chemical composition (wt%, electron microprobe data) is: K 2 O 4.90, CaO 0.04, PbO 1.29, CuO 48.20, ZnO 5.59, Al 2 O 3 0.08, Fe 2 O 3 0.10, P 2 O 5 0.05, As 2 O 5 4.49, V 2 O 5 31.89, SO 3 0.19, MoO 3 2.34, total 99.16. The empirical formula calculated on the basis of 13 O apfu is: (K 0.76 Pb 0.04 Ca 0.01 ) Σ0.81 (Cu 4.45 Zn 0.51 Al 0.01 Fe 0.01 ) Σ4.98 (V 2.58 As 0.29 Mo 0.12 S 0.02 P 0.01 ) Σ3.02 O 13 . Starovaite is triclinic, P –1, a = 6.08(4), b = 8.26(5), c = 10.71(6) A, α = 97.8(1), β = 92.4(1), γ = 90.4(1)°, V = 532(2) A 3 , and Z= 2. The strongest reflections of the X-ray powder diffraction pattern [ d , A ( I , %) (hkl)] are: 10.62 (32) (001); 8.18 (46) (010); 3.047 (41) (022, 200,12-2); 2.745 (47) (2-1-1, 03-1); 2.526 (100) (031, 2-12, 2-1-2, 023, 1-31,13-1); 2.322 (98) (03-3, 21-3, 221, 22-2); 1.867 (23) (302); 1.410 (23) (24-5, 053,41-3, 03-7). Starovaite is a natural analogue of synthetic KCu 5 O(VO 4 )3. The mineral is named in honour of the Russian crystallographer and crystal chemist Galina L. Starova (b. 1946) for her contributions to the crystal chemistry of minerals from the Tolbachik fumaroles.