Belomarinaite KNa (SO 4): A new sulfate from 2012–2013 Tolbachik Fissure eruption, Kamchatka Peninsula, Russia

Abstract

Belomarinaite, ideally KNaSO4,is a new sulphatemineraldiscovered inthe Toludskoe lava fieldformed during Tolbachik Fissure eruptionin 2012–2013. The mineraloccursasarborescent aggregatesof tabular crystals (1×0.3×0.1 mm3) comprising hematite impurities.The average size of the aggregates is 0.5–0.7 mm. The empirical formula is (K0.95Na0.92Cu0.04)S1.01O4. The crystal structure of belomarinaitewas determined using single-crystal X-ray diffraction data:space group P3m1, a= 5.6072(3), c= 7.1781(4) Å, V= 195.45(2) Å3, Z= 2, R1= 2.6%.In the crystal structure of belomarinaite, there are six cation sites: the [4]S(1,2) sites are occupied by S, the [6]Naand [12]Ksites are occupied by Na and K, respectively,giving Na0.5K0.5apfuand the [10]M1 and [10]M2 sites are occupied by Na0.80K0.20and K0.80Na0.20apfu, respectively. The crystal structure is a framework of SO4tetrahedra, Na octahedra and K, M1 and M2 polyhedra.Belomarinaite is isostructural withthe synthetic compound KNaSO4. In belomarinaite, Na and K are disordered over M1 and M2 sites; in its synthetic analogue, Na and K are ordered over M1 and M2 sites, 2respectively. Its Mohs’ hardness is 2–3. The mineral is uniaxial (+), ω = 1.485(3), ε = 1.488(3) (λ= 589 nm). The strongest lines ofthe X-ray powder diffraction pattern (d, Å (I, %) (hkl)) are: 4.022 (31) (101); 3.591 (26) (002); 2.884 (74) (102); 2.800 (100) (110); 2.391 (16) (003); 2.296 (8) 201; 2.008 (38) (022); and 1.634 (10) (212). The mineral was named in honourof Russianvolcanologist Marina Gennadievna Belousova (b. 1960) for her significant contributionstothe monitoring of the Tolbachik Fissure eruption.