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Vol 70, No 9 (2025): VOL 70, NO9 (2025)
Articles
Metal-rich ungrouped chondrite Northwest Africa 13202
Abstract
A meteorite of a new type, NWA 13202, was revealed for the first time in the collection of the Russian Academy of Sciences. It belongs to metal-rich ungrouped chondrites and is paired with chondrites NWA 12379/12273. These chondrites contain on average ~70 vol. % Fe, Ni metal, and ~20 vol. % of chondrules and silicate inclusions imbedded in metal. Similar to other known metal-rich chondrites (G, CH, CBa, and CBb), there is no fine-grained silicate matrix in NWA 13202. Chondrules are represented mainly by porphyritic olivine-pyroxene, olivine and pyroxene types (POP, OP and PP); non-porphyritic chondrules (BO, SO, CC, RC, GC) are rare. Olivine has an L-chondrite chemical composition, Fa25.9 ± 3.5 mol. %, and low-Ca-pyroxene is Fs17.2 ± 5.7 mol. %, which resembles more closely H chondrites. According to the olivine composition heterogeneity, the meteorite corresponds to chondrites of the 3–4 petrological type. Accessory minerals are phosphates and chromite. The metal includes low-Ni kamacite and high-Ni taenite and tetrataenite, and the only sulfide is troilite. The oxygen isotopic composition of chondrule silicates of these ungrouped chondrites confirms their affinities to the oxygen isotope reservoir of LL chondrites (Jansen et al., 2019). The metal experienced partial melting and its formation age is ~2.4 Ma after the formation of Ca,Al – inclusions (Liu et al., 2023). The studied chondrites were probably formed as a result of a catastrophic collision of metallic and chondritic bodies. The intensity and conditions during this event were not sufficient to form chondrules with chondrules of a quenched structure such as CC and SO types. After the reaccretion of a new parent body of the metal-rich ungrouped chondrite, the material of NWA 13202 and NWA 12379/12273 was affected by aqueous alteration and metamorphism at a temperature of ∼600°C, which produced phosphates and rims of Fe-rich olivine around low-Ca pyroxene.
Geochemistry International. 2025;70(9):677-691
677-691
Phosphates in the impact associations of the Chelyabinsk meteorite
Abstract
Na-Fe- and Na-Ca-Mg-Fe-phosphates were found in the impact melt associations of the Chelyabinsk meteorite (Chebarkul fragment). They drastically differ in composition from phosphates of the initial chondrite (chlorapatite, merrillite). Chladniite Na2.25Ca2.14Mg6.47Fe3.76Mn0.17(PO4)9 and merrillite-like phase Na1.32Ca6.80Mg2.07Fe0.98Mn0.04(PO4)7 were observed in silicate part in quenched interstitial groundmass between olivine grains; merrillite and chlorapatite are rare here. The spongy metal-sulfide aggregate from large voids and metal-sulfide blebs in silicate part contain Na-Fe-phosphate globules. They consist of sarcopside and graftonite (Fe2+,Mn2+)3(PO4)2, galileiite Na(Fe2+,Mn2+)4(PO4)3, xenophyllite Na4(Fe2+,Mn2+)7(PO4)6 and unidentified Na-Fe-phosphate Na2(Fe2+,Mn2+)17(PO4)12, sometimes chromite-2. Dendritic-skeletal growth of crystals, evidencing about very rapid quenching, is clearly fixed in all associations of the impact melt (silicate part, vugs, metal-sulfide aggregate, metal-sulfide blebs, and phosphate globules). The following crystallization sequence is revealed in the Na-Fe-phosphatic globules: chromite-2 → sarcоpside/graftonite → galileiite → xenophyllite. It is suggested that their formation was due to separation of Na-Fe-phosphate liquid from homogenous Na-P-Cr-O-dopped Fe-Ni-metal-sulfide melt. Crystallization of Na-Ca-Mg-Fe-phosphates occurred without participation of any liquation processes; and directly from silicate melt. The paper provides data on chemical composition and Raman spectroscopy for all studied phosphates, as well as for the key minerals of the impact melt associations of the Chelyabinsk meteorite.
Geochemistry International. 2025;70(9):692-715
692-715
Unique mineral association and the first finding of extraterrestrial ferrodimolybdenite in the Kunya-Urgench H5 chondrite
Abstract
The mineral ferrodimolybdenite (FeMo2S4) and the associated mineral assemblage were identified for the first time in an extraterrestrial environment: in a sulfide–metal veinlet of the Kunya-Urgench (H5) ordinary chondrite. They were studied using optical microscopy, SEM, EPMA, and EBSD. Ferrodimolybdenite was found as an inclusion in troilite in terrestrial pyrometamorphic rocks in 2023. Its synthetic analogue has been known as a semiconductor since 1960. Experimental data and properties of the natural mineral assemblage suggest that ferrodimolybdenite should have crystallized from troilite melt at a temperature close to 1100–1000 °C. The quenching of metal–sulfide melt enriched in Mo, Cu, and Mn probably formed the metastable phase FeMo2S4 in association with native copper, alabandite, and mercury sulfides. The presence of alabandite can indicate strongly reducing conditions (logfO2 < –4 IW), which are atypical of the impact melting of ordinary chondrites. The fact that this phenomenon occurs locally suggests that a reducing agent may have been locally involved, which was probably a carbon phase contained in the groundmass of the chondrite or brought from the meteoroid that initiated the impact event with the formation of the veinlet. The anomalously high concentrations of Mo (∼103 to 104 CI), Mn, Cu, and Hg in the Fe–S melt could not have been reached either during the fractional crystallization of large volumes of Fe–FeS melt or during the recurrent partial melting of metal sulfide and silicates during impact events. The ferrodimolybdenite and associated mineral phases were most likely formed during the impact melting of an foreign sulfide–metal aggregate that had been formed under conditions different from those characteristic of the formation of the chondrite matrix in which carbonaceous chondrites were presumably formed. An alternative explanation is hydrothermal activity on the parent body of H chondrites. Although prerequisites for this activity have been identified, its P–T boundary parameters remain uncertain.
Geochemistry International. 2025;70(9):716-726
716-726
Thermodynamic properties of oxide compounds occurring in Ca–Al-rich inclusions
Abstract
Based on the analysis of experimental evidence on the high-temperature thermodynamic properties of oxide compounds occurring in Ca–Al-rich inclusions of chondrites, the enthalpies, entropies, and energies of mixing in molten oxide compounds were recommended. They can be used to calculate the activities of oxides and oxide compounds in melts of refractory inclusions in chondrites at temperatures of 1500–2700 K. The advantages and correctness of the developed approach to the obtaining of thermodynamic data were demonstrated by the agreement of calculated evolutionary changes during fractional evaporation of residual melts of Ca–Al-rich inclusions in chondrites and other meteoritic materials with experimental data.
Geochemistry International. 2025;70(9):727-756
727-756
Fe-oxide microspherule fragment from Chang’e-5 soil sample: possible evidence for lunar fumarole activity
Abstract
Earlier discovery of magnetite in the Chang’E-5 regolith raised the question about a source of oxidized material in young basaltic volcanism area of the landing site. Here we report the find of Fe-oxide microspherule fragment found in the Chang’E-5 sample, which retained its original structure suggesting it could be magnetite polyframboid or dendrite-like microspherule. The size and texture of the object suggest its prolonged formation from a Fe-rich oxidized environment. Shape and the growth morphology observed on the microcrystals surface suggest a possible free growth from gaseous or fluid phase. Volcanic gas/fluid accumulated within erupted lava flow could be an oxidizing agent at the late stage of eruption or during post-eruption fumarolic activity. If fumaroles existed in the volcanic complexes of Oceanus Procellarum, then the products should be reworked during regolith gardening afterwards, having preserved traces of such processes in the regolith.
Geochemistry International. 2025;70(9):757-769
757-769
Carbonaceous chondrite clast captured in collision event by the Elga iron meteorite (Group IIE)
Abstract
A melt pocket (MP) found in only one of the silicate inclusions in the Elga iron meteorite was studied using TEM, SEM, EMPA, and Raman spectroscopy methods. The MP demonstrates the liquid immiscibility of the FeCO3–Fe3(PO4)2–SiO2–(Fe, Ni)3P melts, the mineralogical and bulk chemical composition of which is inconsistent with that of the silicate inclusions in the Elga meteorite. Key differences include: (1) The high content of Fe oxide in the MP is inconsistent with the low FeO content (≈3 wt. %) in the SiO2 glass of silicate inclusions; (2) Ca and Mg, the main phase-forming cations of silicate inclusions, are absent in the MP; (3) Siderite and sarcopside, the main oxygen-bearing phases in the MP, were not found in other silicate inclusions of Elga; (4) carbon compounds (aromatized sp2-carbon, phenols) identified in the MP were not found in the host silicate substance. These contradictions lead to the conclusion that the melt pocket is a melted fragment of carbonaceous chondrite captured by Elga’s parent body during a collision with carbonaceous asteroid.
Geochemistry International. 2025;70(9):770-782
770-782