Spinel Group Research Articles

Fe, Zn, and Mg stable isotope systematics of acapulcoite lodranite clan meteorites

AbstractThe processes of planetary accretion and differentiation, whereby an unsorted mass of primitive solar system material evolves into a body composed of a silicate mantle and metallic core, remain poorly understood. Mass‐dependent variations of the isotope ratios of non‐traditional stable isotope systems in meteorites are known to record events in the nebula and planetary evolution processes. Partial melting and melt separation, evaporation and condensation, diffusion, and thermal equilibration between minerals at the parent body (PB) scale can be recorded in the isotopic signatures of meteorites. In this context, the acapulcoite–lodranite meteorite clan (ALC), which represents the products of thermal metamorphism and low‐degree partial melting of a primitive asteroid, is an attractive target to study the processes of early planetary differentiation. Here, we present a comprehensive data set of mass‐dependent Fe, Zn, and Mg isotope ratio variations in bulk ALC species, their separated silicate and metal phases, and in handpicked mineral fractions. These non‐traditional stable isotope ratios are governed by mass‐dependent isotope fractionation and provide a state‐of‐the‐art perspective on the evolution of the ALC PB, which is complementary to interpretations based on the petrology, trace element composition, and isotope geochemistry of the ALC. None of the isotopic signatures of ALC species show convincing co‐variation with the oxygen isotope ratios, which are considered to record nebular processes occurring prior to the PB formation. Iron isotopic compositions of ALC metal and silicate phases broadly fall on the isotherms within the temperature ranges predicted by pyroxene thermometry. The isotope ratios of Mg in ALC meteorites and their silicate minerals are within the range of chondritic meteorites, with only accessory spinel group minerals having significantly different compositions. Overall, the Mg and Fe isotopic signatures of the ALC species analyzed are in line with their formation as products of high‐degree thermal metamorphism and low‐degree partial melting of primitive precursors. The δ66/64Zn values of the ALC meteorites demonstrate a range of ~3.5‰ and the Zn is overall isotopically heavier than in chondrites. The superchondritic Zn isotopic signatures have possibly resulted from evaporative Zn losses, as observed for other meteorite parent bodies. This is unlikely to be the result of PB differentiation processes, as the Zn isotope ratio data show no covariation with the proxies of partial melting, such as the mass fractions of the platinum group and rare earth elements.

Low-Cost Self-Reconstructed High Entropy Oxide as an Ultra-Durable OER Electrocatalyst for Anion Exchange Membrane Water Electrolyzer.

Future energy loss can be minimized to a greater extent via developing highly active electrocatalysts for alkaline water electrolyzers. Incorporating an innovative design like high entropy oxides, dealloying, structural reconstruction, in situ activation can potentially reduce the energy barriers between practical and theoretical potentials. Here, a Fd-3m spinel group high entropy oxide is developed via a simple solvothermal and calcination approach. The developed (FeCoMnZnMg)3O4 electrocatalyst shows a near equimolar distribution of all the metal elements resulting in higher entropy (ΔS≈1.61R) and higher surface area. The self-reconstructed spinel high entropy oxide (S-HEO) catalyst exhibited a lower overpotential of 240mV to reach 10mA cm-2 and enhanced reaction kinetics (59mV dec-1). Noticeably, the S-HEO displayed an outstanding durability of 1000h without any potential loss, significantly outperforming most of the reported OER electrocatalysts. Further, S-HEO is evaluated as the anode catalyst for an anion exchange membrane water electrolyzer (AEMWE) in 1m, 0.1m KOH, and DI water at 20 and 60°C. These results demonstrate that S-HEO is a highly attractive, non-noble class of materials for high active oxygen evolution reaction (OER) electrocatalysts allowing fine-tuning beyond the limits of bi- or trimetallic oxides.

SpinelVA. A new perspective for the visual analysis and classification of spinel group minerals

SpinelVA. A new perspective for the visual analysis and classification of spinel group minerals

Gemological and Spectral Characteristics of Gem-Quality Blue Gahnite from Nigeria

Gem-quality blue octahedral crystalline gahnite was produced in Nigeria. This paper investigated gemological and spectroscopic characteristics by basic gemological experiments, electron probes, infrared reflectance spectroscopy, laser Raman spectroscopy, photoluminescence spectroscopy, and ultraviolet-visible spectroscopy. The results show that the refractive index (RI) of Nigerian gahnite is 1.792∼1.794, and the specific gravity is 4.45∼4.66, with no fluorescence. The main chemical composition is ZnAl2O4, accounting for 93.57%, and the rest is mainly FeAl2O4, which also contains Na, Mg, Co, Mn, Cr, Cu, Si, K, and Ca elements. The infrared spectra showed midinfrared absorption bands near 510 cm−1, 559 cm−1, and 664 cm−1 in the fingerprint region, corresponding to the Zn-O stretching vibration, bending vibration, and Al-O bending vibration, respectively. The Raman spectra showed three of the five Raman active modes of the spinel group, with characteristic Raman absorption peaks located at 418 cm−1, 508 cm−1, and 660 cm−1, corresponding to Eg, T2g(2), and T2g(3) modes, respectively, and the comparison revealed a higher degree of Zn and Al ordering in this paper for gahnite. The photoluminescence spectra show the common Cr3+-activated fluorescence splitting peaks of natural spinel, of which the 686 nm (R-line) fluorescence peak is obvious and sharp. The UV-vis absorption spectra located at 444 nm and 489 nm are the most obvious, which are caused by the d-d electron leap of TFe2+ (5E ⟶ 5T2), and the blue-gray tones of the samples are mainly caused by the spin-forbidden electronic transitions in TFe2+ and MFe2+ ↔ MFe3+; the weak absorption peak at 609 nm was determined to be associated with Co2+ by derivative spectra.

Streamlined Synthesis of Clopidogrel Utilizing Magnetically Recyclable Fe3O4 Nanoparticles through the Strecker Reaction

Aim: The study explores the use of magnetite nanoparticles for eco-friendly α-aminonitrile synthesis via the Strecker reaction, aiming to provide a more efficient, cost-effective, and sustainable method. Methods: The research involves an extensive exploration of magnetite nanoparticles, belonging to the inverse spinel group, as catalysts for the Strecker reaction. The magnetic properties of Fe3O4 nanoparticles facilitate their easy removal from reaction masses using an external magnet, eliminating the need for conventional filtration or centrifugation methods. Trimethylsilyl cyanide (TMSCN) is utilized as a cyanide ion source, known for its efficiency and user-friendly characteristics, aiming to enhance the eco-friendliness of the synthesis. Results: Magnetite nanoparticles with FCC oxygen arrangement and Fe2+ and Fe3+ ions show potential applications in medical and organometallic chemistry. High saturation magnetization, low toxicity, and biocompatibility make them promising for drug delivery and MRI contrast agents. Conclusion: The research presents an environmentally friendly Strecker reaction method using Fe3O4 nanoparticles, offering a promising alternative to traditional methods for α-aminonitrile synthesis and demonstrating the potential of magnetite nanoparticles.

RELAÇÕES ENTRE DENSIDADE RELATIVA E DUREZA EM ALGUNS GRUPOS DE MINERAIS ISOESTRUTURAIS, POLIMÓRFICOS E DE SÉRIES ISOMÓRFICAS (DE SOLUÇÕES SÓLIDAS)

It is undeniable the importance of the physical properties, density and hardness, for mineral diagnosis, and this study aims to demonstrate the possible proportional relationships that exist between these properties in certain groups of isostructural, polymorphic, and isomorphic minerals. For this, different mineral groups were chosen for the construction of tables, systematically arranged based on ascending density orders, with the intention of scrutinizing the possible variations, or lack thereof, in the hardness property. There was an observation of a lack of proportional relationship between these physical properties for all minerals in some of these groups, but generally with a direct or inverse proportionality between two or more minerals. This result is reinforced by the behavior of isostructural minerals such as in the rutile group, where a direct relationship between rutile and stishovite is observed, while an inverse relationship prevails among the others. The isomorphic hexagonal group of hematite (simple oxides) serves as a pertinent illustration of an inversely proportional relationship between hardness and density. In contrast, the direct proportional correlation between these properties is adequately characterized within the spinel group, particularly evident in the chromite series.

Composition of olivines and spinel group minerals in aillikites from the Bushkanay dike, South Siberian Craton: Insights into alkaline melt sources and evolution

The potential sources and conditions that control the formation and evolution of alkaline melts are far from being fully understood. To address some of these fundamental questions, we have focused on the composition of olivines and spinel group minerals in aillikites from the Bushkanay dike in the Siberian Craton. These ultramafic carbonate-rich lamprophyres contain 40-50 vol% fresh olivine macrocrysts (200-600 µm) within a groundmass consisting of phlogopite (60%), magnetite (15%), perovskite (10%), apatite (5%), calcite (3%), chromite (1%), clinopyroxene (up to 1%), barite (up to 1%), serpentine and chlorite (up to 4%). Two types of compositional zoning in olivine have been recognized: (1) Mg-rich cores consisting of a relatively high #Mg (86-89) and NiO (0.25-0.4 wt%); (2) Fe-rich cores with a relatively low #Mg (82-86) and NiO (0.10-0.25 wt%). Both types of olivine cores are igneous and crystallize from an ultramafic carbonate-rich melt. The Mg#-poor (Fe-rich) cores were derived from an early and more evolved aillikitic melt and were later entrained by a more primitive melt, responsible for the formation of the Mg#-rich (Mg-rich) cores. The spinels exhibit a more complex zoning with four major growth zones: (1) an aluminum chromite core; (2) an Fe-chromite and Cr-magnetite transitional zone; and (3) a Ti-magnetite rim. The most primitive spinels of Al-chromite compositions crystallized directly from undifferentiated pulse of the melt, while further growth involved a gradual decrease in Cr due to the crystallization of Cr-rich spinels, while Al remained the same due to the absence of early phlogopite. Our results on olivines and spinels suggest that the aillikites of the Bushkanay dike were derived from a phlogopite-bearing carbonatized peridotite source. This idea is also supported by the presence of phlogopite, calcite, and amphibole as major phases in the chromite melt inclusions.

The origin of olivine basalts from Medvezhya Mount (Avachinsky group of volcanoes, Kamchatka): The evidence of assimilation of sulfide-bearing cumulates

The role and conditions of liquid immiscibility and crystallization of sulfide phase during evolution of subduction related magmas remains to be a debated topic, which bears relevance to mechanisms of porphyry copper deposit formation and evolution of the continental crust. We studied rare volcanic rocks with inclusions of magmatic sulfides in olivine – the basalts of Medvezhya Mount in the Avachinsky group of volcanoes. The rocks belong to primitive (Mg# = 66 mol. %) middle-K island arc olivine basalts. Olivine with normal zoning predominate (~98%) among phenocrysts. The olivine compositions are typical for Kamchatka basalts, except for an unusual trend of increase of MnO content from 0.20 to 0.55 wt. % and decrease of Fe/Mn from 60 to 35 with change of olivine composition from Fo87.8 to Fo78.2. Olivines of this group contain numerous inclusions of minerals of the spinel group varying in composition from chromium spinel to magnesian magnetite. Olivine phenocrysts with sulfide inclusions are characterized by the absence or weak reverse zoning and reduced contents of Ca, Ni, Mn, Cr, and Al. The estimated crystallization temperatures for olivines of the prevailing type are 1036–1241°C, for sulfide-bearing olivines – 1010–1062°C. The data suggest that crystallization of the main olivine population occurred under relatively shallow conditions and was accompanied by strong oxidation of the magmas. On the contrary, the zoning and composition features of sulfide-bearing olivine suggest its xenogenic origin and probable crystallization at conditions of deep crust from low temperature water-rich and/or low-Ca magmas. The results obtained confirm the possibility of saturation of oxidized island-arc magmas with sulfide phase at lower crustal conditions, but show that this process is rare and not typical for low-pressure crystallization stage.

Compositions of Kimberlite Melts: A Review of Melt Inclusions in Kimberlite Minerals

This work is a comprehensive review of existing data on melt inclusions entrapped in minerals of kimberlite rocks emplaced in different cratonic settings at different times. The crystallized melt inclusions represent snapshots of kimberlite melts at different stages of their evolution. All inclusions are composed of daughter minerals and shrinkage bubbles, but no aqueous fluids and quenched silicate glasses have been so far found. More than 60 mineral species were identified among the daughter phases in the inclusions, however, such diverse phase assemblages are typical of all kimberlites studied to date. Daughter minerals are represented by various Na-K-Ca-, Na-Ca-, Na-Mg-, K-Ca-, Ca-Mg-, Ca-, Mg-, Na-carbonates, Na-Mg- and Na-carbonates with additional anions Сl–, \({\text{SO}}_{4}^{{2 - }},\) \({\text{PO}}_{4}^{{3 - }},\) alkali- sulfates, chlorides, phosphates, sulfides, oxides and silicates. Alkali carbonates, sulfates, and chlorides are usually absent among groundmass minerals the majority of kimberlites in the world, except the Udachnaya-East kimberlite in Siberia. On the other hand, this paragenesis in association with traditional kimberlite minerals, such as olivine, micas, monticellite, spinel group minerals, perovskite, rutile, ilmenite, calcite, and dolomite, is common in the crystallized melt inclusions in all studied kimberlites. Carbonates (~30 to 85 vol. %) always dominate over silicates (only up to 18 vol. %) within inclusions. All inclusions also contain variable (2 to 55 vol. %.) amounts of chlorides (halite and sylvite). When relatively low abundances of carbonate minerals (30–50 vol. %) are observed in the inclusions, chlorides (18–55 vol. %) appear to take over other minerals, including silicates that are traditionally considered as main components of “ultramafic” kimberlite parental melts. The published results on melt inclusions in the kimberlite minerals strongly imply that parental kimberlite melts were generated and further evolved within the Na2O-K2O-CaO-MgO-CO2-Cl system, that is, they were alkali-rich carbonatite/carbonatite-chloride liquids. According to various estimates, the SiO2 content in kimberlite melts at different stages of their evolution could have varied from the first to 19 wt. %. Obviously, during and after of а kimberlite bodies formation, interaction with external waters leads to serpentinization of kimberlite olivine and dissolution of a significant part of kimberlite igneous minerals, such as alkaline carbonates, sulfates, and chlorides. In the traditional approach to studying kimberlites, the role of components such as Na2O, CO2, Cl, and to a lesser extent K2O and S, F in the petrogenesis of kimberlite magmas and rocks have been largely underestimated, while olivine- and serpentine-forming components, such as of SiO2, MgO and H2O are still overestimated in contemporaneous literature.

Origin of Fe Ti mineralization in the Late Jurassic to Early Cretaceous Kahnouj ophiolitic complex, Makran accretionary prism, SE Iran

The Kahnouj ophiolitic complex is part of the large Makran accretionary prism, SE Iran, and from the base to top consists of ultramafic-mafic rocks (Band-e-Zeyarat complex), diabase sheeted dikes, and volcanic rocks (Dar Anar complex). The Late Jurassic to Early Cretaceous (156 to 121 Ma) Kahnouj crustal section consists of layered gabbros with ultramafic sill-like bodies at the base that grade upward into variable isotropic gabbros. The Fe Ti ore mineralization of the Dar Gaz district is hosted within the central part of the Kahnouj complex, consisting of coarse-grained gabbro (152.7 ± 5.1 Ma), fine-grained pyroxene-hornblende gabbro, hornblende gabbro (126.5 ± 1.6 Ma), diabase dikes (122.1 ± 2.4 Ma), and granitoid rocks associated with minor feldspathic wehrlite. Economic oxide mineralization (up to 25% FeO + TiO 2 ) is mainly composed of: (1) Intergrown titanomagnetite (containing up to 19 wt% TiO 2 and 0.26 to 1.74 wt% V 2 O 3 ) and ilmenite with hercynite and chromian spinel exsolutions at their boundaries; (2) ilmenite lamella (containing up to 52 wt% TiO 2 and 1 to 3 wt% V 2 O 3 ) in titanomagnetite; and (3) discrete oxide minerals and minor sulfides displaying interstitial textures with formed by fractional crystallization and gravitational settling. Microtextures in the coarse-grained gabbro imply that water-rich fluids migrated along grain boundaries in a ductile regime, causing partial melting and growth of secondary hornblende, An-rich plagioclase, oxide mineral refertilization, and spinel group minerals developed at the boundaries between ilmenite and titanomagnetite. • Kahnouj ophiolitic complex (KOC) formed in the Late Jurassic to Early Cretaceous in a back-arc basin. • The Dar Gaz Fe Ti mineralization is hosted within the central part of KOC in isotropic gabbros. • The Oxide mineralization formed by gravitational settling of intercumulus oxide liquids. • Later partial melting of coarse-grained gabbros generated a melt with more Fe Ti mineralization.

Influential trivalent ion (Cr3+) substitution in mixed Ni–Zn nanoferrites: Cation distribution, magnetic, Mossbauer, electric, and dielectric studies

Herein, we report the influence of trivalent chromium (Cr3+) ion substitution on the electric, dielectric, and hyperfine interaction properties of a mixed Ni–Zn nanoferrite system synthesized by an auto combustion solution-gelation route. The XRD analysis verified the monophase nanocrystalline formation of prepared ferrites belonging to the spinel group with a cubic structure. TEM images displayed the sphere-like morphologies of the typical nanoferrite sample. FT-IR spectra uncover the occurrence of two absorption frequency bands in the desired region belonging to spinel ferrite. The magnetic parameters decreased significantly with increasing Cr3+ concentration. Mossbauer parameters, such as the hyperfine field, line-width, isomer shift and quadrupole splitting, were deduced for all the samples. DCR studies confirmed the semiconducting behavior of all the samples with an increasing resistivity trend after Cr3+ substitution. The dielectric study showed a decreasing trend with an increase in Cr3+ concentration. All the results display the influential substitution of Cr3+ ions in the Ni–Zn ferrite system, which shows the usability of the prepared samples in higher frequency ranging systems.

MINERALOGICAL FEATURES AND SUBSOLIDUS STRUCTURES OF IZRANDITES FROM ALEXANDROVSK COMPLEX

This article presents the results of studying the compositions of rock-forming and accessory ultramafic minerals of izrandite samples from Alexandrovsk metamorphic complex. It was found that petrographical, mineralogical and compositional features indicate igneous cumulative origin of studied rocks but amazing freshness of izrandite contradict with their “oldest age”. Together with igneous, numerous occurrences of subsolidus structures were found in studied rocks. These are following: reaction rims on the olivine-plagioclase boundaries, orthopyroxene-pargasite symplectite intergrowths on the olivine-augite and olivine-plagioclase boundaries, ilmenite and Ti-magnetite lamellae in clinopyroxene and amphibole grains, Ti-magnetite solid-solution breakdown structures. It is shown that spinel group mineral grains have complex structure including different blocks: Ti-magnetite with ilmenite exsolution lamellae, homogenous ilmenite and high-Al spinel, and these were probably formed by subsolidus processes. We have considered critically some scenarios of izrandite origin. We infer that izrandites are similar to cumulative rocks from some cratonic layered intrusions, but it is necessary to note that there is no hard evidence of that izrandite is relict of the oldest protolith of metamorphic rocks.

Minerály coronaditové skupiny z Třebíče - Boroviny a Řípova (Morava, Česká republika)

Localities Třebíč - Borovina (GPS N 49° 12.400‘ E 015° 51.280‘) and nearby Řípov (N 49° 12.700‘ E 015° 50.850‘) are known since 19th century. They represent variegated residual rocks originated during Tertiary? weathering of marbles, dolomite marbles, calcic and magnesian skarns, quartzites and hornblendites intersected by aplites and granitic pegmatites. These rocks enveloped by the biotite gneisses and migmatites close to the contact with the Třebíč Pluton belong to the Moldanubian Zone of the Bohemian Massif. In the past, there was a short-time production of Fe-ore from the weathering zone at Třebíč - Borovina, as well as production of mineral raw-material for brickworks. Since the localities are inaccessible for a long time, we investigated 11 mineral samples of manganese oxidic minerals deposited in the museum collections (Museum Vysočina Třebíč, National Museum in Prague - Natural History Museum, Museum of the South-eastern Moravia in Zlín): 10 from Borovina and 1 from Řípov, labeled as pyrolusite, psilomelane, and wad. They usually form botryoidal black aggregates up to 20 cm in size. Powder X-ray diffraction proved the presence of the coronadite group minerals, accompanied by birnessite (one sample), kaolinite, quartz, gypsum, and minerals of the spinel and chlorite groups. Unit-cell parameters of the coronadite group minerals range as follows: a = 9.750 - 9.939 Å, b = 2.851 - 2.869 Å, c = 9.840 - 10.024 Å, and β = 88.66 - 90.77° (for the monoclinic space group 2/m). Scanning electron microscopy showed the botryoidal texture, where at least part of the zoning visible in back-scattered electrons is in fact the result of density of the mineral aggregate, alternating from massive to fibrous, sometimes with the atol microstructure. Empirical average mineral formulae, based on WDS analyses, are: hollandite from Borovina (Ba2+0.40 Ca2+0.16Mg2+0.13Cu2+0.03Zn2+0.02Pb2+0.01K+0.18Na+0.04)Σ0.98 [(Mn4+5.90Si4+0.06P5+0.04)Σ6.00 (Mn1.77Fe0.20Al0.11)3+Σ2.07] Σ8.07O16, cryptomelane from Borovina (K+0.51Na+0.04Ba2+0.20Ca2+0.09Zn2+0.05Cu2+0.03Mg2+0.02Pb2+0.02Co2+0.01)Σ0.97 [(Mn4+6.91 Si4+0.03P5+0.06)Σ7.00(Mn0.72Fe0.07Al0.06)3+Σ0.85]Σ7.85O16, and cryptomelane from Řípov (K+0.66Na+0.03Ba2+0.14Ca2+0.04 Zn2+0.03Cu2+0.01)Σ0.92[(Mn4+6.88Si4+0.03P5+0.09)Σ7.00 (Mn0.77Al0.11 Fe0.04)3+Σ0.93] Σ7.93O16. Most significant are substitutions Al3+ → Mn3+-1 and Fe3+ → Al3+-1 at the M3+ site, also Mg2+ → Ba2+-1 and Ca2+ → Ba2+-1 at the A2+ site in hollandite. Accessory minerals - baddeleyite and probable xenotime-(Y), present in the hollandite and cryptomelane aggregates, were identified only by EDS analyses.

Rational design of platinum assimilated 3-D zinc cobalt oxide flowers for the electrochemical detection of caffeine in beverage and energy drink

In this work, platinum nanoparticles (Pt) decorated on a spinel group, zinc cobalt oxide (ZnCo2O4) 3-D flower was intended to detect caffeine electrochemical sensor. Pt particles were used to enhance the performance of hydrothermally prepared 3-D ZnCo2O4 flower. So Pt nanoparticles were decorated on each thin nanosheet of self-assembled 3-D flower-like ZnCo2O4. The thin transparent nanosheet of the ZnCo2O4 flower will benefit electrochemical sensors by simplifying its ion exchange. Therefore, Pt@ZnCo2O4 shows an excellent electrochemical conductivity, which promotes the caffeine-based sensor's rapid electrochemical oxidation. Using amperometric i-t at an applied potential of 1.45 V, Pt@ZnCo2O4 modified electrode shows widespread of two linear ranges (0.05 to 265.55 μM and 295.55 to 757.55 μM) with a low detection limit (0.0114 and 0.01657 μM) and high sensitivity (3.419 and 1.862 μA μM−1 cm−2). Moreover, good results were obtained for the real-time detection of caffeine in sugar-free cola beverage and energy drink samples. Henceforth, the developed method could be an ideal way to detect caffeine in real samples.

Bipolar self-doping in ultra-wide bandgap spinel ZnGa2O4

The spinel group is a growing family of materials with general formulation AB2X4 (the X anion typically being a chalcogen like O and S) with many advanced applications for energy. At the time being, the spinel zinc gallate (ZnGa2O4) arguably is the ternary ultra-wide bandgap bipolar oxide semiconductor with the largest bandgap (∼5eV), making this material very promising for implementations in deep UV optoelectronics and ultra-high power electronics. In this work, we further demonstrate that, exploiting the rich cation coordination possibilities of the spinel chemistry, the ZnGa2O4 intrinsic conductivity (and its polarity) can be controlled well over 10 orders of magnitude. p-type and n-type ZnGa2O4 epilayers can be grown by tuning the pressure, oxygen flow and cation precursors ratio during metal-organic chemical vapor deposition. A relatively deep acceptor level can be achieved by promoting antisites (ZnGa) defects, while up to a (n > 1019 cm−3) donor concentration is obtained due to the hybridization of the Zn–O orbitals in the samples grown in Zn-rich conditions. Electrical transport, atomic and optical spectroscopy reveal a free hole conduction (at high temperature) for p-ZnGa2O4 while for n-ZnGa2O4 a (Mott) variable range hopping (VRH) and negative magnetoresistance phenomena take place, originated from “self-impurity” band located at Ev+ ∼3.4 eV. Among arising ultra-wide bandgap semiconductors, spinel ZnGa2O4 exhibit unique self-doping capability thus extending its application at the very frontier of current energy optoelectronics.

Compositional Variations of Spinels from Ultramafic Lamprophyres of the Chadobets Complex (Siberian Craton, Russia)

Ultramafic lamprophyres (UMLs) are mantle rocks that provide important information about the composition of specific carbonate–silicate alkaline melts in the mantle as well as the processes contributing to their origin. Minerals of the spinel group typically occur in UMLs and have a unique “genetic memory.” Investigations of the spinel minerals from the UMLs of the Chadobets complex show the physicochemical and thermodynamic features of the alkaline rocks’ crystallization. The spinels of these UMLs have four stages of crystallization. The first spinel xenocrysts were found only in damtjernite pipes, formed from mantle peridotite, and were captured during the rising of the primary melt to the surface. The next stages of the spinel composition evolution are related to the high-chromium spinel crystallization, which changed to a high-alumina composition. The composition then changed to magnesian ulvöspinel–magnetites with strong decreases in the Al and Cr amounts caused by the release of carbon dioxide, rapid temperature changes, and crystallization of the main primary groundmass minerals such as phlogopite and carbonates. Melt inclusion analyses showed the predominance of aluminosilicate (phlogopite, clinopyroxene, and/or albite) and carbonate (calcite and dolomite) daughter phases in the inclusions that are consistent with the chemical evolution of the Cr-spinel trend. The further evolution of the spinels from magnesian ulvöspinel–magnetite to Ti-magnetite is accompanied by the formation of atoll structures caused by resorption of the spinel minerals.

Archean–Ediacaran evolution of the Campos Gerais Domain — A reworked margin of the São Francisco paleocontinent (SE Brazil): Constraints from metamafic–ultramafic rocks

The Campos Gerais Domain (CGD) in southeastern Brazil is an approximately 180 km × 35 km area of Archean–Proterozoic rocks located southwest of the São Francisco Craton (SFC). The Archean–Paleoproterozoic evolution of the CGD — alongside its potential correlation with the SFC or other cratonic blocks in the region — is currently poorly-constrained. We present the results of systematic petrography, bulk-rock geochemistry, mineral chemistry and geochronology for a suite of scarcely studied mafic–ultramafic rocks from the CGD. We also provide a compilation of previously reported bulk-rock geochemical and spinel group mineral chemical data for mafic–ultramafic rocks throughout the CGD, and geochronological information for various lithotypes in the region. The CGD records a protracted Mesoarchean to Statherian (3.1–1.7 Ga) crustal evolution, which we interpret to share a common history with the southern SFC and their related reworked segments, suggesting that it is a westward extension of this cratonic terrain. The metavolcano-sedimentary rocks of the Fortaleza de Minas and Alpinópolis segments represent a Mesoarchean greenstone belt that is stratigraphically and chemically comparable to Archean greenstone belts worldwide, and that is broadly coeval with a local suite of tonalite-trondhjemite-granodiorite (TTG) gneisses and migmatites. U-Pb SHRIMP zircon data from a subalkaline metagabbro yielded a concordia age of ca. 2.96 Ga, revealing a previously unrecognized phase of Archean magmatism in the CGD that can be chrono-correlated with metakomatiite and TTG generation elsewhere in the São Francisco paleocontinent. Our data contradict a hypothesis whereby the metavolcano-sedimentary rocks of the Jacuí-Bom Jesus da Penha and Petúnia segments represent an ophiolite, as previously suggested, instead presenting features that point to formation in association with a continental arc. Coupled with a U-Pb (SHRIMP) crystallization age of ca. 2.13 Ga recorded by zircon grains from a metaultramafic rock, these data highlight that a magmatic event was chrono-correlated with the main accretionary phase of the Minas Orogeny, and with the Pouso Alegre/Amparo and São Vicente complexes. Finally, a U-Pb (SHRIMP) concordia age of ca. 590 Ma — obtained from metamorphic-textured zircon grains from a metaultramafic rock — points to a late metamorphic overprint related to upper amphibolite conditions, brittle fault activation and the juxtaposition of crustal blocks in association with the latest stages of western Gondwana’s assembly in the southern SFC, with later retrogression to greenschist-facies.

Petrogenesis of Zr–Nb (REE) carbonatites from the Arbarastakh complex (Aldan Shield, Russia): Mineralogy and inclusion data

The Arbarastakh Neoproterozoic ultramafic carbonatite complex is located in the southwestern part of the Siberian Craton (Aldan Shield) and contains ore-bearing Zr–Nb (REE) carbonatites and phoscorites. Carbonatites are mainly represented by calcite and silicocarbonatite varieties. The primary minerals composing the carbonatites are calcite and dolomite, as well as phlogopite, clinopyroxene, fluorapatite, amphibole, fluorite, K-feldspar and feldspathoids. Olivine (forsterite), Ti-magnetite, apatite, phlogopite, calcite, dolomite and the minor spinel group minerals form the primary phoscorites. The ore-bearing Zr–Nb mineral assemblages of the phoscorites and carbonatites include accessory zircon, zirconolite, perovskite, pyrochlore and baddeleyite. The Ba–Sr–REE hydrothermal mineralisation consists of ancylite-(Ce), bastnaesite-(Ce) and burbankite, as well as barite-celestite, strontianite, barytocalcite, and rare Cu–Fe sulphides. The silicocarbonatites and carbonatites formed in multiple stages from a single alkaline Ca–Na–K–silicocarbonatite melt, while the phoscorites are products of differentiation of the carbonatitic melt and were crystallised from an Fe-rich phosphate–carbonate melt at temperatures of more than 720 °C. The silicate–phosphate–carbonate melts were responsible for the Zr–Nb mineralisation of the carbonatites at temperatures of more than 540–575 °C; the hydrothermal REE-bearing mineral assemblages crystallised from saline (60–70 wt%) carbonatitic fluids of Na–Ca–Mg–F–carbonate composition at a minimum temperature range of 350–300 °C. The Ca–Sr-carbonate as well as the Na–hydro–carbonate fluids were responsible for the Ba–Sr–REE mineralisation of the phoscorites at ~500–480 and 450–430 °C.

Еволюція мезозойських перидотитів угольського офіолітового комплексу (мармароська скельна зона, внутрішні українські Карпати)

The paper presents the results of the study of peridotites of the Ugolka ophiolite complex of the Inner Ukrainian Carpathians. The work is based on the data of prior research and original materials of geological observations from the middle course of the Tereblya River, and on new laboratory analyzes of peridotites. Middle Triassic – Lower Cretaceous (?) Peridotites of the Ugolka ophiolite complex form olistolites in the Lower Cretaceous olistostrome-conglomerates of Soimul formation. Petrographic data make it possible to classify disparate olistolites of the ophiolite complex, and peridotites in particular, into two types of ophiolite associations, which were formed in different conditions according to indicator minerals (including spinelides). Results of the study of spinelites form two groups that correlate with two equilibrium mineral associations: first – olivine + spinel + orthorhombic pyroxene + monoclinic pyroxene; and second – amphibole + talc. Larger isometric or xenomorphic individuals of chromium spinels are found in harzburgites and lherzolites. Smaller chromium spinel individuals form elongated and elliptical grains, stretched along the structure of the rock, and are found in the interstices of pyroxene and olivine crystals. X-ray microprobe analysis revealed that the composition of chromium spinel grains of the first group contains more magnesium and less chromium. chromium spinels of the second group are smaller, and contain less magnesium and more chromium. On the binary diagram Cr#–Mg# chromium spinels from the peridotites of the Ugolka complex are concentrated in two areas: abyssal peridotites and suprasubduction peridotites. chromium spinel grains from the first group crystallized at a low degree of partial melting (Dmelt up to 14 %), which is typical for abyssal peridotites. chromium spinels of the second group crystallized at a higher degree of melting (Dmelt up to 30 %), which is characteristic of peridotites of suprasubduction zones. On the correlation diagram of the average chromium spinel and the total spreading speed, the chromium spinel compositions of the first group of the Ugolka complex corresponds to the peridotites of ultra-slow spreading zones. Small grains from the second group of chromium spinels of the Ugolka complex are associated with peridotites of fast spreading zones. The temperature of metamorphism of rocks of the first mineral association is estimated by spinel and olivine-spinel geothermometers, and is contained within range of 900–1 290 ºС, at pressure aprox. 15 kbar. The temperature of metamorphism of rocks forming the second mineral association, I estimated at 430–450 °C, at pressure of 4.0–4.5 kbar. The study of peridotites of the Ugolka complex is informative for reconstruction of the geological evolution of the original sediments and determining the stages of formation of thrust-nappe structures.

Analysis of dielectric properties of zinc aluminum silicate based ceramic nanoparticles

Abstract Zinc Aluminate (ZnAl2O4) is a class of spinel group which has unusual characteristics and recognised as the microwave dielectric ceramic. Zinc Aluminate based silicon (ZnAl2O4) compound nanomaterial is suitable for the microwave applications due to its low dielectric permittivity low tangent loss and the improved conductivity. In this work, we present the sol–gel synthesis of ZnAl2O4SiO2 ceramic nanoparticles and investigations using X-ray diffraction (XRD), Raman spectroscopy, and field-emission scanning electron microscopy (FESEM). XRD study revealed the amorphous nature of the sample. Raman measurement showed the vibration peaks of TiO2-Eg modes originated at 143 cm−1 and 631 cm−1 along with a peak at 391 cm−1 ascribed to the B1g mode of SiO2. We noticed almost constant dielectric permittivity at room temperature with the increased frequency however, an increased permittivity is observed with the increased frequency at increased temperature from 40 to 150 °C. In a similar fashion, we observed low dielectric loss in higher frequency regime at increased temperature from 40 to 150 °C. Furthermore, we explored the conductivity and impedance analysis of ZnAl2O4SiO2 ceramic nanoparticles in the view of their applicability as the microwave ceramic material.