Typical characteristics of many anhydrous sulphates of exhalative origin at fumaroles at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia, are the presence of additional oxygen atoms (Oa) in the composition. Recent field works on the fumaroles of the Second scoria cone in 2014 and 2015 resulted in discovery of a new mineral species, puninite, and collection of fresh alumoklyuchevskite and kamchatkite samples which allowed the re-refinement of crystal structures. The crystal structure of kamchatkite, KCu3O(SO4)2Cl, was solved and refined in Pnma space group (a = 9.755(2), b = 7.0152(15), c = 12.886(3) Å, V = 881.8(3) Å3, R1 = 0.021), whereas alumoklyuchevskite, K3Cu3 AlO2(SO4)4, is triclinic, P1¯ (a = 4.952(3), b = 11.978(6), c = 14.626(12) Å, α = 87.119(9), β = 80.251(9), γ = 78.070(9)°, V = 836.3(9) Å3, R1 = 0.049) in contrast to previously reported data.

The new mineral puninite, ideally Na2Cu3O(SO4)3, was found in sublimates of Glavnaya Tenoritovaya fumarole. The mineral is named in honor of the Russian crystallographer Yurii Olegovich Punin (1941–2014). Puninite is closely associated with lammerite-β, tenorite, hematite and anhydrite. Puninite is emerald-green in colour. It is biaxial, optically positive, α = 1.587(2), β = 1.611(2), γ = 1.649(2), 2Vcalc = 60°. The mineral is soluble in water. The empirical formula of puninite based on 13 O atoms is (Na1.76K0.08)Σ1.84(Cu2.97Zn0.04)Σ3.01(SO4)3.02O0.92. Puninite is the first Na-dominant copper oxosulfate mineral observed on Second scoria cone. It is monoclinic, C2/c, a = 17.41(1), b = 9.39(1), c = 14.40(1) Å, β = 112.04(7)°, V = 2183(2) Å3, Z = 8. The eight strongest lines of the X-ray powder diffraction pattern are (I-d-hkl): 100-8.058-200, 18.88-6.675-002¯, 28.47-6.466-202¯, 14.1-4.398-202, 17.37-4.247-113¯, 33.89-3.839-022¯, 29.15-2.854-224¯, 14.95-2.724-024¯. Puninite is structurally related to euchlorine, NaKCu3O (SO4)3 and to fedotovite, K2Cu3O(SO4)3. The unit-cell a parameter value is very sensitive to the K-Na ratio in “euchlorine group” minerals. The crystal structure of puninite (R1 = 0.035) is based on oxocentred [O2Cu6]8+ dimers. Four sulphate tetrahedra are ‘face-to-face’ attached to the dimers, whereas the other sulphate tetrahedral groups provide their linkage in two dimensions. The structural architecture of all the copper-oxosulphate exhalative minerals described in this paper can be described as being organized via a “host–guest” principle.

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