IMA 2018-149b = petrovite

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Marco E. Ciriotti
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IMA 2018-149b = petrovite

Messaggio da Marco E. Ciriotti » mar 30 giu, 2020 8:57

Prossima pubblicazione.

▪ Filatov, S.K., Shablinskii, A.P., Krivovichev, S.V., Vergasova, L.P., Moskaleva, S.V. (2020): Petrovite, Na10CaCu2(SO4)8, a new fumarolic sulfate from the Great Tolbachik fissure eruption, Kamchatka Peninsula, Russia. Mineralogical Magazine, 84, (in press).

Petrovite, Na10CaCu2(SO4)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 Na6(Na1.80K0.20)Σ2Na(Ca0.82Na0.06Mg0.02)Σ0.90(Cu1.84Mg0.16)Σ2(Na0.52□0.48)Σ1S8.12O32. The crystal-chemical formula is CuNa6-2xCax(SO4)4, which, for x ~ 0.5, results in the idealized formula Na10CaCu2(SO4)8. The crystal structure of petrovite was determined using single-crystal X-ray diffraction data; the space group is P21/c, a = 12.6346(8), b = 9.0760(6), c = 12.7560(8) Å, β = 108.75(9)º, V = 1385.1(3) Å3, Z = 2 and R1 = 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 CuO7 polyhedra, which share corners with SO4 tetrahedra to form isolated [Cu2(SO4)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), βcalc = 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); 3.65(34)(22–1). The mineral is named in honor of Prof. Dr. Tomas Georgievich Petrov (b. 1931) for his contributions to mineralogy and crystallography and, in particular, for the development of industrial technology of fabrication of jewelry malachite.
Marco E. Ciriotti

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