Belomarinaite KNa(SO4): A new sulfate from 2012-2013 Tolbachik Fissure eruption, Kamchatka Peninsula, Russia

Belomarinaite, ideally KNaSO4, is a new sulfate mineral discovered in the Toludskoe lava field, formed during the 2012-2013 Tolbachik Fissure eruption. The mineral occurs as arborescent aggregates of tabular crystals (1 mm x 0.3 mm x 0.1 mm) comprising hematite impurities. The average size of the aggregates is 03-0.7 mm. The empirical formula is (K0.93Na0.92Cu0.04)(Sigma 1.91)S-1.O-01(4). The crystal structure of belomarinaite was determined using single-crystal X-ray diffraction data; the space group is P3m1, a= 5.6072(3), c = 7.1781(4) angstrom, V = 195.45(2) angstrom(3), Z = 2 and R-1 = 2.6%. In the crystal structure of belomarinaite, there are six cation sites: the ([4])S1 and ([4])S2 sites are occupied by S, the Na-[6] and K-[12] sites are occupied by Na and K, respectively, giving Na0.5K0.5 apfu and the ([10])M1 and ([10])M2 sites are occupied by Na(0.78)k(0.22) and K0.78Na0.22 apfu, respectively. The crystal structure is a framework of SO4 tetrahedra, Na octahedra and K, M1 and M2 polyhedra. Belomarinaite is isostructural with the synthetic compound KNaSO4. In belomarinaite, Na and K are disordered over MI and M2 sites; in its synthetic analogue, Na and K are ordered over M1 and M2 sites, respectively. The Mohs' hardness is 2-3. The mineral is uniaxial (+), with omega = 1.485(3) and epsilon = 1.488(3) (lambda = 589 nm). The strongest lines of the powder X-ray diffraction pattern [d, angstrom (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 honour of Russian volcanologist Marina Gennadievna Belousova (b. 1960) for her significant contributions to the monitoring of the Tolbachik Fissure eruption.