Vol 148, No 5 (2019)

General section

Systematic of polymorphous transformation of crystals, generalized on the base of M.J. Burger’s criteria

Filatov S.K., Paufler P.


The paper proposes an extended (3 × 3) classification of polymorphous transformations, which includes the 0th coordination sphere in addition to the M. J. Burger’s I and II coordination spheres. As a result, the first parameter of this classification is the number of a transformable coordination sphere — it takes the value equal to 0 (atom, ion), 1 (the coordination polyhedra) and 2 (the nearest to the coordination polyhedra environment). The second parameter of the classification is determined by the Burger’s energy barrier for a transformation. And here, in addition to transformations with a break of chemical bonds (reconstructive) and without it (deformational), some intermediate types of transformations take place — with a disordering of structural units (atoms, molecules and other atomic complexes). As examples of polymorphous transformations with transformation of the 0th coordination sphere, there are considered electron transitions in an atom, changes of the atom’s spin, and magnetic ordering of atoms in a crystal structure. Transformations with disordering are illustrated by substitutions-jumps of structural units and their slowed down or free rotation. There is developing the concept of “polymorphism” of chemical elements.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):1-23
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Modeling of mineral parageneses and thermobarometry of metavolcanic rocks of the Ruker group in the southern Prince Charles Mountains, East Antarctica

Gulbin Y.L., Mikhalsky E.V.


There are diverse geological complexes that expose at Prince Charles Mountains and form the crystalline basement of the East Antarctic Platform. One of them is the Ruker Metasedimentary Group that is a part of the Palaeproterozoic-Neoproterozoic suprastructure of the Ruker Terrane and is divided into two sequences of metasedimentary and metavolcanic rocks, highly deformed and metamorphosed in greenschist facies. In order to estimate metamorphic conditions in this group, mineral and major element compositions of metavolcanic rocks were studied and isochemical phase diagram were calculated with the Theriak/Domino program. Mafic schists contain the mineral assemblage Chl—Ep—Ab—Qz—Ttn ± Act ± Bt ± Ms ± Cal that is typical of metabasites, and which varies with the bulk rock composition and ratio of components in a water-carbon dioxide fluid involved in phase reactions. The calculated mole fraction of CO2 in the fluid equilibrated with carbonate-bearing parageneses lies in a range between 0.13 and 0.27. The chloritoid schist is essentially composed of Cld, Chl, Ms, and Rt. It is debated whether this rock is genetically related to metamorphism of laterites derived from the basalts. Results of forward thermodynamic modeling, supplemented by chlorite-phengite thermobarometry, indicate that metamorphism of the Ruker Group occurred under conditions of high-P part of the greenschist facies (temperature 300—450 °C, pressure up to 7—8 kbar). These conditions significantly higher than the stable continental geotherm and is close to temperatures and pressures corresponding to those along the slow subduction geotherm. According to available geological data, the same geodynamic setting may have taken place in a course of the evolution of the Neoproterozoic intraplate sedimentary basin in connection with sinking of parts of the basement at large depth as a consequence of tectonic aggregation during the closure of the basin.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):24-44
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New Minerals

Deltalumite, a new natural modification of alumina with spinel-type structure

Pekov I.V., Anikin L.P., Chukanov N.V., Belakovskiy D.I., Yapaskurt V.O., Sidorov E.G., Britvin S.N., Zubkova N.V.


The new mineral deltalumite, an analogue of the spinel-type synthetic δ-Al2O3, the second, after corundum α-Al2O3, natural modification of alumina, was found in products of two eruptions of the Ploskiy Tolbachik Volcano (Kamchatka, Russia). It occurs in pores of basalt lava and basalt scoria altered by fumarolic gas. The mineral forms roundish aggregations up to 0.2 mm across which consist of blocky, coarse prismatic individuals up to 0.03 mm in size. Deltalumite is pale yellowish, pale beige or white, translucent, with vitreous lustre. The mineral is brittle. Dcalc = 3.663 g cm–3. Deltalumite is optically uniaxial (–), ω = 1.654(2), ε = 1.653(2) (λ = 589 nm). Chemical composition (electron microprobe) is: Al2O3 99.74, SiO2 0.04, total 99.78 wt %. The strongest reflections of powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 2.728(61)(202), 2.424(51)(212), 2.408(49)(213), 2.281(42)(206), 1.993(81)(1.0.11, 220, 221), 1.954(48)(0.0.12) and 1.396(100)(327, 400, 2.1.14). The mineral is tetragonal, space group P-4m2 (by analogy with synthetic δ-Al2O3), unit-cell dimensions are: a = 5.608(1), c = 23.513(7) Å, V = 739.4(4) Å3 and Z = 16. Deltalumite belongs to the spinel subgroup within the oxyspinel group, its structural formula can be written as (Al0.670.33)Al2O4 in which □ means vacancy. The new mineral can be clearly distinguished from other modifications of alumina using powder X-ray diffraction pattern or IR spectrum.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):45-58
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Minerals and parageneses of minerals

Defect and admixture composition of diamond crystals with growth pyramids <100> from placers of the Krasnovishersky district, the Urals

Klepikov I.V., Vasilev E.A., Antonov A.V.


The internal structure of cuboid diamonds from contemporary alluvial placers of the Krasnovishersky district at the Urals was investigated with analyzing their spectroscopic characteristics. Crystals were divided into four groups by their anatomy and spectroscopic features: cuboids of the II variety in the Yu. L. Orlov classification; cuboids with transparent core and outer part saturated with inclusions; crystals with simultaneous growth of <100> and <111> pyramids, and crystals with their consecutive growth. The local photoluminescence investigations have been carried out for all different growth zones and pyramids. There was revealed localization of luminescence bands 926 and 933 nm to growth pyramids <100> and <111>. In all studied crystals, the last stage of growth was the regenerative formation of {111} face steps together with square pits forming on the surface. Some cuboids with C centres have specific luminescence systems, such as 575, 635.1, 636.8 nm, broad band with maximum at 700 nm, and intense lines at 800, 820.5, 840, 860, 869 nm. Different thermal history of mixed-habit diamonds was shown. It is noted that the cuboid diamonds from different regions of the world have the similar internal structure and spectroscopic features.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):59-73
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Mineral composition of paleoproterozoic metamorphosed massive sulfide ore in the Kola Region (a case study of the Bragino Occurrence, South Pechenga)

Kompanchenko A.A., Voloshin A.V., Bazai A.V.


Many occurrences and deposits of massive sulfide ores in the Kola Region are connected with the Paleoproterozoic Pechenga—Imandra—Varzuga Rift Belt (2.5—1.7 Ga). They are placed in volcanogenic-sedimentary complexes of South Pechenga (Bragino occurrence) and western part of Imandra-Varzugskaya structural zones (Pyrrhotite Ravine deposit, Tahtarvumchorr occurrence, etc.). The age of massive sulfide ore formation is expected to be about 1.9 Ga. The ores and their host complexes were metamorphosed under conditions close to the amphibolite facies. High degree of metamorphism of massive sulfide ores of the Kola region determined the features of their mineral composition, which are considered on the example of the Bragino occurrence. The article displays ore types, their mineral assemblages, and data on main minerals of ores: pyrrhotite, pyrite, sphalerite, marcasite, etc.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):74-88
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Cr-spinels in carbonate veins of the Onguren Complex (Western Baikal Region)

Savelyeva V.B., Bazarova E.P., Khromova E.A.


Cr-spinels in carbonate veins of the Ongurensky complex (Eastern Siberia, Western Baikal region) are mainly represented by ferrichromite and crommagnetite (MgO ≤0.3 wt %, Mg# ≤0.04, Al2O3 ≤2.5 wt%; Cr# 0.91—1.00, Fe2+/Fe3+ 0.8—1.4) with a high content of ZnO (0.9—4.6 wt %). In the calcite vein, titanium chrommagnetite is transformed into chromium-containing titanomagnetite, which decomposes into less titanium magnetite and ilmenite at 970—1000 °С and fO2 is about +0.5 ÷ +0.7 QFM. In the dolomite vein, ferrichromite and chrommagnetite grains contain relic cores of subferrialumochromite (Al2O3 10.6—14.4 wt %, Cr# 0.63—0.73, Fe2+/Fe3+ 4.1—5.2, MgO ≤0.52 wt %) with increased amounts of ZnO (3.7—5.1 wt %), TiO2 (3.2—4.1 wt %), and MnO (0.6—1.1 wt %). Ferrichromite and chrommagnetite are formed during high-temperature (>600 °C) metamorphism of the vein. Superimposed deformations in conditions of greenschist facies lead to the formation of magnetite rims around the grains of chromomagnetite.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):89-112
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Platinum-bearing of chromitites from the Kurtushibinsky ofiolite belt, Western Sayan: new data

Yurichev A.N., Chernyshov A.I.


Small scattered grains of PGE minerals have been found in chromitites of Ergaksky and Kalninsky ultramafic massifs, which are extreme northeastern fragments of the Kurtushibinsky Ophiolite Belt of Western Sayan. For the first time, together with previously known PGE minerals, there were found the Cu—Ru—Os solid solution, arsenic-bearing (As up to 3.6 wt %) laurite with minor Pt, Ni, and Co, PGE sulfides of MeS and Me3S4 types, sulfoarsenide with the high content of Rh (~12.7 wt %) in chromitites of the Ergaksky massif, and laurite and sulfoarsenides in chromitites of the Kalninsky massif. Compositions of PGE minerals indicate high temperature of the Ru—Os sulfide formation (~1200—1250 ºC) in both massifs, as well as high partial pressure of sulfur under the formation of chromitites and syngenetic PGE minerals in the Ergaksky massif. PGE mineral assemblages were formed in several stages. Os—Ir—Ru solid solutions and disulfides of the laurite—erlichmanite series (mainly fractionating ruthenium) formed earlier than Cu—Ru—Os solid solutions, sulfides (Ru,Fe)3S4, (Ru,Ni,Fe)S, and PGE sulfoarsenides, which crystallized under influence of reduced fluids as a result of remobilization and redeposition of PGE. 

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):113-125
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New data on malanite and cuprorhodsite from chromitites of the Bushveld Complex, South Africa

Rudashevsky N.S., Rudashevsky V.N.


The 3D mineralogical technology was used to study the representative selection of grains of thiospineles from 3 groups of chromitite horizons (lower LG6, middle MG1/MG2 and upper UG2): 46 grains of malanite (4—42 μm) and 34 grains of cuprorhodsite (9—42 μm). Their microprobe analysis was performed (n = 61). Statistics for this selection have resulted in following formulae: for malanite — (Сu2+,Fe2+)(Pt3+,Rh3+,Ir3+,Co3+,Ni3+Fe3+)2S4, for cuprorhodsite — (Сu2+,Fe2+) ∙ ∙ (Rh3+,Pt3+,Ir3+,Fe3+)2S4. According to morphological properties and their relationship with platinum-group minerals (PGM) and base metal sulphides, thiospinel can be attributed as the earliest primary PGM in chromitites. The distribution of cuprorhodsite and malanite in chromitites was controlled by the Rayleigh fractionation of the primary sulfide melt in the process of formation of Bushveld chromitite horizons.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):126-134
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Experimental mineralogy

On the conditions of the formation of cancrisilite Na7(Al5Si7O24)(CO3) · 3H2O and «hydroxycancrinite» Na6(Al6Si6O24) · 4H2O (on the basis of data on synthesis)

Chukanov N.V., Kotel'nikov A.R., Pekov I.V., Van K.V.


Aluminosilicates with a cancrinite-type structure compositionally related to cancrisilite and a Ca-free and CO3 — deficient cancrinite analogue were synthesized and characterized by electron microprobe and HCN-analyses, IR spectroscopy, and powder X-ray diffraction. The empirical formulae of the compounds obtained are H0.05Na6.13[Al4.36Si7.64O24](CO3)0.91 · 2.85H2O and H0.07Na6.19[Al5.53Si6.47O24]· ·(CO3)0.365 · 3.915H2O, respectively. The latter compound is characterized by disordered chains (···Na···H2O) in the narrow channel and a high content of H2O in the wide channel. The conditions for the formation of cancrisilite and carbonate-deficient cancrinite varieties in nature are discussed. It was concluded that supercritical conditions and ultra-agpitic environment contribute to crystallization of cancrisilite.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019;148(5):135-144
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