Hermannjahnite, CuZn(SO4)2, a new mineral with chalcocyanite derivative structure from the Naboko scoria cone of the 2012–2013 fissure eruption at Tolbachik volcano, Kamchatka, Russia

Abstract

A new mineral hermannjahnite, ideally CuZn(SO4)2, was found in the sublimates of Saranchinaitovaya fumarole, Naboko scoria cone, where the recent Fissure Tolbachik Eruption occurred in 2012–2013. The cotype specimen was found in the Arsenatnaya fumarole, on the Second scoria cone of the Great Tolbachik Fissure Eruption (GTFE 1975–1976). The mineral is named in honour of Hermann Arthur Jahn. Jahn-Teller effect is pronounced in the structure of hermannjahnite. The empirical formula of the holotype hermannjahnite, calculated on the basis of 8 O apfu is: Cu1.00(Zn0.43Cu0.31Mg0.25)∑0.99S2.00O8. Hermannjahnite is optically biaxial (+), α = 1.642(2), β = 1.652(2), γ = 1.675(2) (589 nm) with 2 V (calc.) = 67.6°. Hermannjahnite is monoclinic, P21/n, a = 4.8076(2), b = 8.4785(3), c = 6.7648(3) A, β = 93.041(3) °, V = 275.35(2) A3, Z = 2, R 1 = 0.047. The eight strongest lines of the X-ray powder diffraction pattern are (I-d-hkl): 31–4.231-(020), 100–4.177-(110), 72–3.630-(11–1), 25–3.486-(111), 29–2.681-(11–2), 69–2.648-(02–2), 29–2.561-(112), 63–2.428-(130). The structure of hermannjahnite is isotypic to that of dravertite, CuMg(SO4)2, and represents a monoclinically distorted chalcocyanite CuSO4 structure. Crystallographic and structural data on a natural sample of chalcocyanite are provided. Zinc is very close in ionic radii to copper, but the Jahn-Teller effect on Cu2+ causes the segregation of these elements over two symmetrically independent crystallographic sites in hermannjahnite. Bond-length distortion parameters (∆oct) were evaluated for 44 different MO6 (M = Cu, Zn) octahedra in Cu, Zn oxysalt minerals containing Cu- or/and Zn-dominated octahedra. In hermannjahnite CuO6 octahedra exhibit a value of ∆oct × 103 = 14.71, whereas ∆oct × 103 = 0.83 is calculated for ZnO6. In chalcocyanite CuO6 octahedra have a value of ∆oct × 103 = 8.25. Relationships between calculated ∆oct parameters and occupancy of MO6 (M = Cu, Zn) octahedra by Cu2+ and Zn2+ cations in various minerals are evaluated and discussed.