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

Abstract

AbstractBelomarinaite, 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 × 0.3 mm × 0.1 mm) comprising hematite impurities. The average size of the aggregates is 0.5–0.7 mm. The empirical formula is (K0.95Na0.92Cu0.04)Σ1.91S1.01O4. The crystal structure of belomarinaite was determined using single-crystal X-ray diffraction data; the space group isP3m1,a= 5.6072(3),c= 7.1781(4) Å,V= 195.45(2) Å3,Z= 2 andR1= 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[6]Na and[12]K sites are occupied by Na and K, respectively, giving Na0.5K0.5apfu and the[10]M1 and[10]M2 sites are occupied by Na0.78K0.22and K0.78Na0.22apfu, respectively. The crystal structure is a framework of SO4tetrahedra, Na octahedra and K,M1 andM2 polyhedra. Belomarinaite is isostructural with the synthetic compound KNaSO4. In belomarinaite, Na and K are disordered overM1 andM2 sites; in its synthetic analogue, Na and K are ordered overM1 andM2 sites, respectively. The Mohs’ hardness is 2–3. The mineral is uniaxial (+), with ω = 1.485(3) and ε = 1.488(3) (λ = 589 nm). The strongest lines of the powder X-ray 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 honour of Russian volcanologist Marina Gennadievna Belousova (b. 1960) for her significant contributions to the monitoring of the Tolbachik Fissure eruption.