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

A new mineral hermannjahnite, ideally CuZn(SO 4 ) 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: Cu 1.00 (Zn 0.43 Cu 0.31 Mg 0.25 ) ∑0.99 S 2.00 O 8 . 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, P 2 1 / n, a = 4.8076(2), b = 8.4785(3) , c = 6.7648(3) Å, β = 93.041(3) ° , V = 275.35(2) Å 3 , 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(SO 4 ) 2, and represents a monoclinically distorted chalcocyanite CuSO 4 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 Cu 2+ causes the segregation of these elements over two symmetrically independent crystallographic sites in hermannjahnite. Bond-length distortion parameters (∆ oct ) were evaluated for 44 different M O 6 ( M = Cu, Zn) octahedra in Cu, Zn oxysalt minerals containing Cu- or/and Zn-dominated octahedra. In hermannjahnite CuO 6 octahedra exhibit a value of ∆ oct × 10 3 = 14.71, whereas ∆ oct × 10 3 = 0.83 is calculated for ZnO 6 . In chalcocyanite CuO 6 octahedra have a value of ∆ oct × 10 3 = 8.25. Relationships between calculated ∆ oct parameters and occupancy of M O 6 ( M = Cu, Zn) octahedra by Cu 2+ and Zn 2+ cations in various minerals are evaluated and discussed.