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AbstractUsing selected aeria difraction and X-ray powder data, a structural model was constructed for the rare mineral vyalsovite FeCaAlS(OH)5. Parameters of the elementary monoclinic cell а 5.205, b 21.402, c 14.400 Å, β 95°, sp. gr. Cm. The crystal structure of vyalsovite is the first example of a hybrid structure composed of commensurate iron sulfide and hydroxide modules.

The results of detailed exploration and year-round observations of the hydrogeological regime at large deposits, as well as special hydrochemical studies of various types of water and changes in the gas composition of the underground atmosphere in the lateritic weathering crust, of the very large bauxite-bearing province, Fouta Djallon–Mandingo, thanks to a reliable factual base, made it possible for the first time to draw a number of important conclusions about the conditions and features of zoning formation in the lateritic weathering profile. The weathering profile consists of two metasomatic columns spatially combined in plan, but vertically separated: an upper one, consisting of hydroxides and oxides of iron and aluminum, and a lower one, composed of clayey eluvium and products of hydration and decomposition of aluminosilicates—polymineral clays and kaolinite. In both columns, the processes of change begin with the same rainwater, but differ in the hydrodynamic parameters in each of the columns. Changes in the weathering profile occur in accordance with the main patterns of low-temperature infiltration metasomatism. The modern hydrogeological and gas regime in bauxite-bearing lateritic covers controls the mineralogical and geochemical zoning. Features of biological and soil processes and hydrodynamics and hydrochemistry in the weathering profile lead to a threshold nature of the change in physicochemical and biochemical conditions, providing the action of geochemical (oxidation, reduction, gley, adsorption) barriers, which is the main mechanism of zonal distribution of matter in lateritic weathering crusts.

AbstractThe Central bauxite deposit on the territory of the Russian Federation is a unique geological object. It hosts both primary lateritic bauxites and products of their redeposition (sedimentary lateritic bauxites). The comparative characteristic of the residual in situ lateritic bauxites and sedimentary lateritic bauxites and the study of the morphology of ore-forming minerals of bauxites and their composition allowed us to reconstruct in details the genesis of laterite profiles and sedimentary bauxite-bearing deposits, which has universal significance for understanding supergene mineral deposits. The prospects of using bauxites for REE by-products is shown by the example of the Central deposit of the Chadobets Uplift.

AbstractFor the first time, a series of long-term taphonomic experiments (1–5 years) has shown iron deposition during the formation of fossils of soft-bodied animals. Based on the set of measurements, it is concluded that the deposition of iron is not a factor of preservation of soft-bodied animal remains, and pyritization itself is a consequence of chemical processes in iron-containing sediments. These reactions are triggered by the decomposition of organic matter and are accompanied by the destruction of minerals and saturation of the liquid medium with dissolved iron. The nonexclusive, common nature of these reactions in the sediments explains the cosmopolitan distribution of pyritized fossils of soft-bodied organisms. Such an explanation is an alternative to the prevailing opinion on pyritization: iron serves as the main preservation agent and pyritization takes place with the participation of sulfate reducers accelerating the deposition of iron on the organic matrix.

AbstractThe main source of aluminum is bauxite ores and their basic mineral components gibbsite Al(OH)3 and boehmite AlO(OH). Alumina Al2O3 is formed by various methods of decomposition of these components, electrolytically decomposed to pure Al. It has been established that gibbsite is the basic and often the only mineral of aluminum in the Mesozoic and Cenozoic laterite bauxites, representing most of the world’s reserves. Boehmite is formed in laterite-sedimentary bauxites, during lateritization and desilication of albic water-sedimentary continental sediments, as well as the underlying bleached parent rocks. The formation of boehmite is associated with an excess of aluminum generally due to its input from above. Boehmite predominates in the Paleozoic laterites. The formation of aluminum monohydrate is explained by a decrease in the oxidation–reduction potential.

AbstractThe mineral and chemical composition of bauxites from the Chadobets uplift of the Siberian Platform is the total product of laterites on aluminosilicate rocks (source of aluminum) and on alkaline rocks and carbonatites (source of rare earth elements (REEs), Nb, Ta, Th, U, etc.). The laterization of these rocks and subsequent denudation led to the formation of unique bauxite deposits with a high content of rare and REEs. Supergene minerals of the laterite weathering crust are in a dispersed microcrystalline and amorphous state, which complicates their study and the choice of methods for extracting useful components. Precision methods were used to establish the forms and compositions of the main supergene minerals, biomineral films, biomorphoses, and the distribution of rare and rare earth elements in them.

AbstractA structural model of the rare mineral yushkinite [(Mg0.60Al0.30V0.10)Σ1.0(OH)2] [V0.875S2] is studied using the data of electron microdiffraction and the X-ray powder pattern. The parameters of the elementary trigonal cell are а = 3.25 Å and с = 11.40 Å, with the space group \\(P\\, 3 m1\\). The structure is composed of brucite and sulfide layers alternating along the с-axis, which are commensurate in the basal plane. The layer structure determines the finely dispersed nature of yushkinite morphology and perfect cleavage along 001. The idealized yushkinite formula is refined, and trigonal symmetry is established in contrast to the hexagonal one proposed earlier.

AbstractIn the course of additional exploration of the lower horizons of the unique Sangaredi deposit in West Africa, nonlaterized deposits of the Sangaredi series of all major lithological types were found. The lithological composition of redeposited bauxitized deposits of the Sangaredi series varies from conglomerate- and gritstone–bauxites to sandstone-like and clayey bauxites, which facially represent water-sedimentary (alluvial and lacustrine) continental deposits. The appearance of such a propitious redeposited parent substrate predetermined the formation of sedimentary-lateritic bauxites as a result of subsequent laterization. In this article the main processes are characterized and the stages of the formation of extra-quality bauxites of the unique Sangaredi deposit are substantiated.

AbstractIn this paper, the authors synthesize and study the phase formation of yttrium–iron garnet (YIG) using the supercritical antisolvent precipitation technique (SAS) at the initial stage for the first time. The effect of supercritical CO2 on the solution of acetates in the quasi-equilibrium state causes an abnormally high mobility of the structure’s elements. As a result, it becomes possible to form the equilibrium phase of the YIG solid product directly (without the appearance of transition oxides) at temperatures much lower than by solid-phase synthesis. The temperature decrease is due to a significant decrease in the activation energy of the solid solution.

AbstractFor the first time, a systematic electron microscope study of the complete weathering of quartz in lateritic bauxites formed on khondalites and alluvial deposits of India was carried out. The appearance of dissolving individuals composing quartz crystals and their permanent connection with abundant biomineral films turned into druses of gibbsite crystals Al(OH)3 are shown. The solubility of quartz is due to its unique piezoelectric properties, abnormal quartz expansion during inversion, climatic features, and intense biochemical factors (organic residues, bacteria, biofilms, etc.).