The crystal structure of dmisteinbergite has been determined using crystals from the type locality in Kopeisk city, Chelyabinsk area, Southern Urals, Russia. The mineral is trigonal, with the following structure: P312, a = 5.1123(2), c = 14.7420(7) Å, V = 333.67(3) ų, R₁ = 0.045, for 762 unique observed reflections. The most intense bands of the Raman spectra at 327s, 439s, 892s, and 912s cm ⁻¹ correspond to different types of tetrahedral stretching vibrations: Si–O, Al–O, O–Si–O, and O–Al–O. The weak bands at 487w, 503w, and 801w cm⁻¹ can be attributed to the valence and deformation modes of Si–O and Al–O bond vibrations in tetrahedra. The weak bands in the range of 70–200 cm⁻¹ can be attributed to Ca–O bond vibrations or lattice modes. The crystal structure of dmisteinbergite is based upon double layers of six-membered rings of corner-sharing AlO₄ and SiO₄ tetrahedra. The obtained model shows an ordering of Al and Si over four distinct crystallographic sites with tetrahedral coordination, which is evident from the average <T–O> bond lengths (T = Al, Si), equal to 1.666, 1.713, 1.611, and 1.748 Å for T1, T2, T3, and T4, respectively. One of the oxygen sites (O4) is split, suggesting the existence of two possible conformations of the [Al₂Si₂O₈]²⁻ layers, with different systems of ditrigonal distortions in the adjacent single layers. The observed disorder has a direct influence upon the geometry of the interlayer space and the coordination of the Ca2 site. Whereas the coordination of the Ca1 site is not influenced by the disorder and is trigonal antiprismatic (distorted octahedral), the coordination environment of the Ca2 site includes disordered O atoms and is either trigonal prismatic or trigonal antiprismatic. The observed structural features suggest the possible existence of different varieties of dmisteinbergite that may differ in: (i) degree of disorder of the Al/Si tetrahedral sites, with completely disordered structure having the P6₃/mcm symmetry; (ii) degree of disorder of the O sites, which may have a direct influence on the coordination features of the Ca²⁺ cations; (iii) polytypic variations (different stacking sequences and layer shifts). The formation of dmisteinbergite is usually associated with metastable crystallization in both natural and synthetic systems, indicating the kinetic nature of this phase. Information-based complexity calculations indicate that the crystal structures of metastable CaAl₂Si₂O₈ polymorphs dmisteinbergite and svyatoslavite are structurally and topologically simpler than that of their stable counterpart, anorthite, which is in good agreement with Goldsmith’s simplexity principle and similar previous observations.

Blue sapphire of gem quality was recently discovered in spinel–chlorite–muscovite rock within meta-ultramafites near the Ilmenogorsky alkaline complex in the Ilmen Mountains of the South Urals. More than 20 minerals were found in the assemblage with the blue sapphire. These sapphire-bearing rocks are enriched in LREE and depleted in HREE (with the negative Eu anomalies) with REE distribution similar to those in miascites (nepheline syenite) of the Ilmenogorsky alkaline complex. ⁸⁷Sr/⁸⁶Sr ratios in the sapphire-bearing rocks varied from 0.7088 ± 0.000004 (2σ) to 0.7106 ± 0.000006 (2σ): epsilon notation εNd is −7.8. The Rb-Sr isochrone age of 289 ± 9 Ma was yielded for the sapphire-bearing rocks and associated muscovite. The blue sapphires are translucent to transparent and they have substantial colorless zones. They occur in a matrix of clinochlore-muscovite as concentric aggregates within spinel-gahnite coronas. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses showed values with trace elements typical for “metamorphic” blue sapphires, with Ga/Mg < 2.7, Fe/Mg < 74, Cr/Ga > 1.5 (when Cr is detectable), and Fe/Ti < 9. Sapphires overlap “metasomatic” at “sapphires in alkali basalts” field on the FeO–Cr₂O₃–MgO–V₂O₃ versus FeO + TiO₂ + Ga₂O₃ discriminant diagram. The sapphires formed together with the spinel-chlorite-muscovite rock during metasomatism at a contact of orthopyroxenites. Metasomatic fluids were enriched with Al, HSFE, and LILE and genetically linked to the miascite intrusions of Ilmenogorsky complex. The temperature required for the formation of sapphire–spinel–chlorite–muscovite rock was 700–750 °C and a pressure of 1.8–3.5 kbar.

Kyshtymites are the unique corundum-blue sapphire-bearing variety of anorthosites of debatable geological origin found in the Ilmenogorsky-Vishnevogorsky complex (IVC) in the South Urals, Russia. Their mineral association includes corundum-sapphire, plagioclase (An_61–93), muscovite, clinochlore, and clinozoisite. Zircon, churchite-(Y), monazite-(Ce), and apatite group minerals are found as accessory phases. Besides, churchite-(Y) and zircon are also identified as syngenetic solid inclusions within the sapphires. In situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb zircon geochronology showed the ages at about 290–330 Ma linked to the Hercynian orogeny in IVC. These ages are close to those of the syenitic and carbonatitic magmas of the IVC, pointing to their syngenetic origin, which is in agreement with the trace element geochemistry of the zircons demonstrating clear magmatic signature. However, the trace element composition of sapphires shows mostly metamorphic signature with metasomatic overprints in contrast to the geochemistry of zircons. The reason for this discrepancy can be the fact that the discrimination diagrams for sapphires are not as universal as assumed. Hence, they cannot provide an unambiguous determination of sapphire origin. If it is true and zircons can be used as traces of anorthosite genesis, then it can be suggested that kyshtymites are formed in a magmatic process at 440–420 Ma ago, most probably as plagioclase cumulates in a magma chamber. This cumulate rock was affected by a second magmatic event at 290–330 Ma as recorded in zircon and sapphire zoning. On the other hand, Ti-in-zircon thermometer indicates that processes operated at relatively lower temperature (<900 °C), which is not enough to re-melt the anorthosites. Hence, zircons in kyshtymites can be magmatic but inherited from another rock, which was re-worked during metamorphism. The most probable candidate for the anorthosite protolith is carbonatites assuming that metamorphic fluids could likely leave Al- and Si-rich residue, but removed Ca and CO₂. Further, Si is consumed by the silicification of ultramafic host rocks. However, kyshtymites do not show clear evidence of pronounced metasomatic zonation and evidence for large volume changes due to metamorphic alteration of carbonatites. Thus, the obtained data still do not allow for univocal reconstruction of the kyshtymite origin and further investigations are required.

Six minor alluvial chromite placers (Kolkhoznyi Prud, Verkhne-Yaushevo, Sukhoy Izyak, Bazilevo, Novomikhaylovka, Kiryushkino) and one major littoral placer (Sabantuy) were found in sandy sediments of the Kazanian stage of the Permian System (Late Roadian and Wordian Stages) in the Southern Pre-Urals. It is shown that the morphological features of chromian spinels are diverse, which is not evidence of the heterogeneity of the source. The bulk chemical composition of chromian spinels from all placers is similar and generally correlates with compositions of chromian spinels from the Kraka ophiolitic complex in the Southern Urals. The morphological diversity of grains, varied chemical composition and presence of melt inclusions in Ti-high octahedral grains of chromian spinels comply with the ophiolitic nature of the source. Thus, there is no need to refer to other sources for chromite ores but ophiolitic. The new placers expand the dissemination area of chromite-bearing deposits on the east edge of the East-European Platform and offer a prospect to discover new placers.

Technogenic steklite, KAl(SO₄)₂, and unnamed mineral phase (K,Na)₃Na₃(Fe,Al)₂(SO₄)₆ from burnt dumps of the Chelyabinsk Coal Basin have been investigated by single-crystal X-ray diffraction and electron microprobe analysis. Steklite is trigonal, space group P$\overline{3}$, a = 4.7277(3), c = 7.9871(5) Å, V = 154.60(2) ų. The crystal structure was refined to R₁ = 0.026 (wR₂ = 0.068). It is based upon the [Al(SO₄)₂]⁻ layers formed by corner sharing of SO₄ tetrahedra and AlO₆ polyhedra. The anionic [Al(SO₄)₂]⁻ layers are parallel to the (001) plane and linked via interlayer K⁺ ions. The regular octahedral coordination of Al is observed that distinguishes technogenic steklite from that found in Tolbachik fumaroles. The (K,Na)₃Na₃(Fe,Al)₂(SO₄)₆ phase is trigonal, space group R$\overline{3}$, a = 13.932(2), c = 17.992(2) Å, V = 3024.4(7) ų, R₁ = 0.073 (wR₂ = 0.108). The crystal structure is based upon the anionic chains [(Fe,Al)(SO₄)₃]³⁻ running parallel to the c axis and interconnected via K⁺ and Na⁺ ions. There are no known minerals or synthetic compounds isotypic to (K,Na)₃Na₃(Fe,Al)₂(SO₄)₆, due to the presence of separate K and Na sites in its structure.

Tourmaline, an intermediate member of the oxyschorl–oxydravite–oxymagnesio-foitite-bosiite series with a predominance of the oxy-dravite-bosiite end-member, was studied from late calcite-quartz veins in the eastern zone of the Murtykty gold deposit (Republic of Bashkortostan). Sulfide mineralization in veins includes rare chalcopyrite, pyrite, sphalerite and galena. Accessory minerals are xenotime-(Y), vanadium-containing rutile and fine high-fineness gold. Supergene mineralization resulted from decomposition of carbonates, sulfides and rock-forming silicates includes kaolinite, hydroxides of Mn (chalcophanite, psilomelane) and Fe (goethite and limonite ochers), mainly developed in vein cavities ; chalcopyrite is replaced by cuprite and malachite. The composition of tourmaline is close to metamorphic dravite of orogenic gold deposits and tourmaline of gold-porphyry deposits, transitioning from porphyry to epithermal. Two possible B sources for the formation of tourmaline are considered: sedimentary rocks of the paleoisland-arc complex and granodiorites of the Mansurovo pluton. Figures 9. Table 1. References 36. Key words: tourmaline, boron, gold, xenotime-(Y), Murtykty deposit, Republic of Bashkortostan.