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Conditions of high-temperature volcano-related mineral formation are a source of the new and rare minerals and their associations; they are rather fragmentarily described for volcanic systems as a whole, except for several objects characterized in this regard. The study aim is to present the first results of the mineralogical study of atypical suprasubduction zone neoformation encountered from the Taketomi flank eruption (1933–1934) of the Alaid volcano (Kuril Islands), which has been studied through electron microprobe analyses and powder and single-crystal X-ray diffraction. The following mineral paragenesis is described: diopside, andradite, anorthite, wollastonite, esseneite, wadalite, rhönite-like mineral, fluorite, calcite, apatite, and atacamite. The parageneses of calcium silicates found in volcanic systems are usually interpreted as reworked crustal xenoliths and commonly associated with volcanoes that have a carbonate basement. However, carbonates have not been previously described at the base of the Alaid volcano. Even though the skarn nature of such a mineral paragenesis is possible, we suggest the important role of high-temperature volcanic gases along with the pyrometamorphic effect in the mineral-forming process at depth or in near-surface conditions (fumarole-like type in the form of a system of cracks and burrows). The described mineral paragenesis has not been previously documented, at least for the North Kuril Islands. A detailed mineralogical study of such formations is one of the important steps in understanding the functioning of magmatic systems, the circulation and transformation of natural matter, and mineral-forming processes. Full article

The new mineral sharyginite, Ca₃TiFe₂O₈ (P2₁ma, Z = 2, a = 5.423(2) Å, b = 11.150(8) Å, c = 5.528(2) Å, V = 334.3(3) ų), a member of the anion deficient perovskite group, was discovered in metacarbonate xenoliths in alkali basalt from the Caspar quarry, Bellerberg volcano, Eifel, Germany. In the holotype specimen, sharyginite is widespread in the contact zone of xenolith with alkali basalt. Sharyginite is associated with fluorellestadite, cuspidine, brownmillerite, rondorfite, larnite and minerals of the chlormayenite-wadalite series. The mineral usually forms flat crystals up to 100 µm in length, which are formed by pinacoids {100}, {010} and {001}. Crystals are flattened on (010). Sharyginite is dark brown, opaque with a brown streak and has a sub-metallic lustre. In reflected light, it is light grey and exhibits rare yellowish-brown internal reflections. The calculated density of sharyginite is 3.943 g·cm^-3. The empirical formula calculated on the basis of 8 O apfu is Ca_3.00(Fe³⁺_1.00Ti⁴⁺_0.86Mn⁴⁺_0.11Zr_0.01Cr³⁺_0.01Mg_0.01)_Σ2(Fe³⁺_0.76Al_0.20Si_0.04)_Σ1.00O₈. The crystal structure of sharyginite, closely related to shulamitite Ca₃TiFeAlO₈ structure, consists of double layers of corner-sharing (Ti, Fe³⁺) O₆ octahedra, which are separated by single layers of (Fe³⁺O₄) tetrahedra. We suggest that sharyginite formed after perovskite at high-temperature conditions >1000°C. Full article

This paper describes an innovative process for the production of ferrochromium alloy via segregation reduction of chromite at 1300 °C in the presence of calcium chloride. Both charcoal and petroleum coke were used as the reductant. Individual polycrystalline ferrochrome carbide particles were produced, with their particle size and shape resembling that of the starting carbon particles. Interactions among calcium chloride, clinochlore, and chromite resulted in the formation of Ca-bearing chromite, wadalite, and gaseous chlorides. Monocrystalline ferrochrome carbide whiskers were formed only when charcoal in the presence of calcium chloride was used to reduce the chromite fraction containing large amounts of siliceous gangue. Incorporating thermodynamic evaluations, a possible segregation reduction mechanism is suggested based on the characterization of the products using scanning electron microscopy, energy dispersive spectroscopy, X-ray powder diffraction, and electron probe microanalysis, combined with thermogravimetric analysis. Metallization within chromite particles was minimized, which is suggested to be due to the ubiquitous presence of molten and gaseous calcium chloride between the chromite and carbon particles, and especially in the porous rim of the chromite particles during reduction, resulting in restricted metallization only on the carbon particles. Full article

A solid reduction process is described whereby chromite is reduced with the help of calcium chloride to produce ferrochrome alloy powders with high metal recovery. The process involves segregation reduction of chromite using graphite as the reductant and calcium chloride as the segregation catalyst. Experiments were performed in the temperature range of 1200–1400 °C to evaluate the influences of various design parameters using both a thermogravimetric analyzer and an electric tube furnace with continuous off-gas analysis. The reduced products were characterized by scanning electron microscopy, X-ray powder diffraction, synchrotron X-ray absorption spectroscopy, and were subjected to wet chemical analysis. It was concluded that the addition of calcium chloride not only accelerated the carbothermic reduction of chromite but also promoted the formation and growth of individual ferrochrome alloy particles. The alloy formation within chromite particles was minimized, enabling the effective separation of ferrochrome alloy particles from the unwanted gangue without the need for fine grinding. Majority of the calcium chloride remained in a recoverable form, with a small percentage (<10 wt %) consumed by reacting with the siliceous gangue forming wadalite. Pure ferrochrome alloy powders were successfully produced with high metal recovery using elutriating separation. Full article