2020/06/30 by С. К. Филатов, A.P. Shablinskii, Sergey V. Krivovichev +2 · 2 citations
Materials Science · Chemistry · Physics and Astronomy · #Crystal Structures and Properties #Inorganic Fluorides and Related Compounds #Advanced Condensed Matter Physics
paper · pdf · doi:10.1180/mgm.2020.53
openalex publication_date 2020/06/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/03
Abstract Petrovite, Na 10 CaCu 2 (SO 4 ) 8 , is a new sulfate mineral discovered on the Second scoria cone of the Great Tolbachik fissure eruption. The mineral occurs as globular aggregates of tabular crystals up to 0.2 mm in maximal dimension, generally with gaseous inclusions. The empirical formula calculated on the basis of O = 32 is Na 6 (Na 1.80 K 0.20 ) Σ2 Na(Ca 0.82 Na 0.06 Mg 0.02 ) Σ0.90 (Cu 1.84 Mg 0.16 ) Σ2 (Na 0.52 □ 0.48 ) Σ1 S 8.12 O 32 . The crystal-chemical formula is CuNa 6−2 x Ca x (SO 4 ) 4 , which, for x ≈ 0.5, results in the idealised formula Na 10 CaCu 2 (SO 4 ) 8 . The crystal structure of petrovite was determined using single-crystal X-ray diffraction data; the space group is P 2 1 / c , a = 12.6346(8), b = 9.0760(6), c = 12.7560(8) Å, β = 108.75(9)°, V = 1385.1(3) Å 3 , Z = 2 and R 1 = 0.051. There are one Cu and six Na sites, one of which is also occupied by the essential amount of Ca. The Cu atom forms five Cu–O bonds in the range 1.980–2.180 Å and two long bonds ≈ 2.9 Å resulting in the formation of the CuO 7 polyhedra, which share corners with SO 4 tetrahedra to form isolated [Cu 2 (SO 4 ) 8 ] 12− clusters. The clusters are surrounded by Na sites, which provide their linkage into a three-dimensional framework. The Mohs’ hardness is 4. The mineral is biaxial (+), with α = 1.498(3), β calc = 1.500, γ = 1.516(3) and 2V = 20(10) (λ = 589 nm). The seven strongest lines of the powder X-ray diffraction pattern [ d , Å ( I , %) ( hkl )] are: 7.21(27)(110); 6.25(38)(102); 4.47(31)(212); 3.95(21)(30 2 ); 3.85(17)(121); 3.70(36)(202); and 3.65(34)(22 1 ). The mineral is named in honour of Prof Dr Tomas Georgievich Petrov (b. 1931) for his contributions to mineralogy and crystallography and, in particular, for the development of technology for the industrial fabrication of jewellery malachite.