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The effect of replacing magnesia by alumina on the pressure-dependent structure of amorphous enstatite was investigated by applying in situ high-pressure neutron diffraction with magnesium isotope substitution to glassy (MgO)0.375(Al2O3)0.125(SiO2)0.5. The replacement leads to a factor of 2.4 increase in the rate-of-change of the Mg–O coordination number with pressure, which increases from 4.76(4) at ambient pressure to 6.51(4) at 8.2 GPa, and accompanies a larger probability of magnesium finding bridging oxygen atoms as nearest-neighbors. The Al–O coordination number increases from 4.17(7) to 5.24(8) over the same pressure interval at a rate that increases when the pressure is above ∼3.5 GPa. On recovering the glass to ambient conditions, the Mg–O and Al–O coordination numbers reduce to 5.32(4) and 4.42(6), respectively. The Al–O value is in accordance with the results from solid-state 27Al nuclear magnetic resonance spectroscopy, which show the presence of six-coordinated aluminum species that are absent in the uncompressed material. These findings explain the appearance of distinct pressure-dependent structural transformation regimes in the preparation of permanently densified magnesium aluminosilicate glasses. They also indicate an anomalous minimum in the pressure dependence of the bulk modulus with an onset that suggests a pressure-dependent threshold for transitioning between scratch-resistant and crack-resistant material properties. [ABSTRACT FROM AUTHOR]

Enstatite (Mg2Si2O6) is a member of the pyroxene group and an important mineral in the lower crust and upper mantle. Enstatite has three phases at ambient pressure: protoenstatite, orthoenstatite, and clinoenstatite. Previously, the polymorphic transformation of pyroxene has been characterized using bulk techniques such as X-ray diffraction of powders. Given that rocks are crystal aggregates, it is important to use aggregates to understand phase transformations. We therefore conducted grain growth and deformation experiments using aggregates of enstatite to investigate phase transformations. Grain growth experiments were conducted at temperatures (T) of 1345 and 1360 °C under a vacuum of ≈ 10 Pa using an alumina tube furnace. Deformation experiments were conducted at T = 1310 °C and room pressure, a strain rate of ≈ 10–4 s–1, and a resulting stress of ≈ 150 MPa. The samples were analyzed using a scanning electron microscope, electron backscatter diffraction (EBSD), and X-ray diffraction. The results indicate that the grain size affects the transformation from protoenstatite to clinoenstatite, whereas deformation by diffusion creep does not. The EBSD analyses show that the volume fraction of clinoenstatite increases with increasing grain size. The samples underwent diffusion creep during the deformation experiments, and there were no distinct microstructural differences between deformed and undeformed samples. The EBSD analyses show that the transformed clinoenstatite has a characteristic twin structure with a misorientation angle of 180° and a rotation axis of [100] or [001]. Grain sizes become smaller during the phase transformation, even if the mechanism can be characterized as a second-order transformation.Highlights: Grain growth and deformation experiments using aggregates of enstatite crystals were conducted to understand the microstructural developments due to the phase transformation from protoenstatite to clinoenstatite. Grain size influences the transformation, whereas deformation by diffusion creep does not. Grain sizes become smaller during the phase transformation, even if the mechanism can be characterized as a second-order transformation. [ABSTRACT FROM AUTHOR]

The infrared spectroscopic properties of selected defects involving one proton and one nearby M3+ (M = Al, Cr, Fe) substitution in orthoenstatite are investigated by first-principles calculations. Based on the theoretical results, the absorption bands experimentally observed on synthetic samples with high crystalline quality and low doping levels can be assigned to specific defect configurations. Most of them correspond to Mg vacancies at M2 sites locally compensated by one proton and one M3+ cation at a nearby M1 site. This confirms that the M3+ + H+ = 2 Mg2+ exchange mechanism is the dominant hydrogen incorporation mechanism at the lowest concentration levels in doped enstatite. At higher concentration levels, more complex incorporation mechanisms could become dominant in Al-bearing samples. [ABSTRACT FROM AUTHOR]

Platinum-group elements (PGE) are most effectively concentrated via sulfide-silicate melt immiscibility; however, under sulfide-undersaturated conditions, PGE may exhibit highly siderophile behavior and occur as native metals and alloys. In this case, they can form micrometer-size inclusions within Cr-spinel, but also large nuggets (up to several kilograms), found in chromitites and related placer deposits. The exact formation mechanism of such large nuggets and accumulations of PGE unrelated to sulfide melts remains controversial due to mass balance issues. In this study of multiphase inclusions in Os-Ir-Ru nuggets from the Adamsfield placer district (Tasmania, Australia), we constrain their crystallization environment. Multiphase inclusions comprise variable proportions of hornblende, enstatite, quartz, anthophyllite, anorthite, chlorite and native iridium and coexist with single-phase olivine and Cr-spinel inclusions. The heterogeneity in phase and chemical composition of the inclusions indicates a complex origin from an inhomogeneous source media. This is corroborated by grain scale disequilibrium mineral assemblages, where forsterite and quartz are both included within a single osmium grain. Our proposed multi-stage origin of Adamsfield Os-Ir-Ru nuggets involved magmatic olivine-Cr-spinel-Os-Ir-Ru cumulates in peridotite bodies that were subsequently overprinted by various hydrothermal and metamorphic processes, including serpentinization or growth of Os-Ir-Ru from supercritical fluids. The final metamorphic stage resulted in the obliteration of Os-Ir-Ru zonation, culminating in the current assemblage of inclusions. [ABSTRACT FROM AUTHOR]

A literature compilation of 1136 low‐Ca pyroxene compositions from chondrules from 12 primitive type 2–3 carbonaceous, ordinary and enstatite chondrite groups define unique regions on an Al2O3 and Cr2O3 diagram when compared to low‐Ca pyroxenes from equilibrated type 4‐6 chondrites. Measured compositions of 100 low‐Ca pyroxenes from comet Wild 2 and a giant cluster IDP of probable cometary origin are similar to each other and fall in the type 2–3 chondrite chondrule region suggesting that most of the pyroxenes likely formed in the solar nebula like conventional chondrules. The data imply that most low Ca‐pyroxenes from comet Wild 2 and the giant cluster IDP formed from igneous crystallization processes and did not experience significant thermal metamorphism, indicating that the low‐Ca pyroxenes were unlikely incorporated into large parent bodies prior to accretion in their respective comet bodies. An intriguing group of nine low‐Ca pyroxenes from comet Wild 2 with low Cr and Al that fall where type 4–6 chondrites are located are interpreted as products of condensation. The compositional data combined with previously measured oxygen isotopes on 17 low‐Ca pyroxenes support earlier conclusions that comet samples have links with carbonaceous, ordinary, and possibly enstatite chondrite groups. Our results provide additional evidence that comets accreted materials from multiple chondrule reservoirs throughout the solar nebula. [ABSTRACT FROM AUTHOR]

Meteoritical Bulletin 112 contains the 2487 meteorites approved by the Nomenclature Committee of the Meteoritical Society in 2023. It includes 14 falls, 1926 ordinary chondrites, 141 HED, 127 carbonaceous chondrites (including 6 ungrouped), 71 lunar meteorites, 37 ureilites, 36 mesosiderites, 27 Martian meteorites, 23 iron meteorites (6 ungrouped), 20 Rumuruti chondrites, 19 ungrouped achondrites, 19 enstatite chondrites, 18 primitive achondrites (2 ungrouped), 12 pallasites, 6 angrites, 4 enstatite achondrites, and 1 ungrouped chondrite. Of the meteorites approved in 2023, 968 were from Africa, 836 from South America, 572 from Antarctica, 66 from Asia, 35 from North America, 9 from Europe, and 1 from Oceania. [ABSTRACT FROM AUTHOR]

Evaporation of silicate materials from Earth or its precursors may be important in shaping their primordial compositions represented by undifferentiated meteorites, e.g., enstatite chondrites; however, the conditions under which evaporation occurs and the extent of evaporation-induced elemental and isotope fractionation remain uncertain. Here, we experimentally determine the volatility and isotope fractionation of Si, Mg, Ca, Nb, and Ta during enstatite melt evaporation at 2423–2623 K using a high-temperature conical nozzle levitator. Homogenous glasses are recovered after experiments; then we use EPMA and LA-ICP-MS to measure the elemental compositions, MC-ICP-MS to measure the Si and Mg isotopes, and TIMS to measure the Ca isotopes. Our results show that the evaporation rates of Si are larger than Mg, and the mean vapor/melt isotope fractionation factors (α = Rvapor/Rmelt; R = isotope ratio) are 0.99585 ± 0.00002 for 29Si/28Si and 0.98942 ± 0.00130 for 25Mg/24Mg. However, neither evaporative loss of Ca, Nb, and Ta nor Ca isotope fractionation was observed within analytical uncertainty. In conjunction with previous studies, we find that in an evaporation experiment the saturation degree (partial vapor pressure/equilibrium vapor pressure) of Si (SSi) is larger than SMg when Si is more volatile than Mg, and vice versa. If the Mg/Ca and Si/Ca ratios and isotopes in the bulk silicate Earth are attributed to the evaporation of enstatite chondrite-like precursors, evaporation temperatures >5000 K and SSi < SMg are required. [ABSTRACT FROM AUTHOR]

In order to understand the origin of oldhamite (CaS) in enstatite meteorites, we report Ca isotopic compositions (δ 44/40Ca) of oldhamite (obtained from water leachate of bulk chondrites and aubrites and mineral separates from the Norton County aubrite) and silicate minerals from different types of enstatite chondrites and aubrite. The δ 44/40Ca of the bulk enstatite chondrites range from 1.05 ‰ to 1.24 ‰, with an average of 1.13 ± 0.12 ‰, higher than that of the estimate of the bulk silicate earth (∼0.94 ‰). Major and trace element analyses show that the water leachates of enstatite chondrites are mainly composed of oldhamite, and they take over 20.6–68.5 % Ca of the bulk meteorite Ca budget. The Ca isotope fractionation between oldhamite and residual silicate (Δ44/40Ca oldhamite-silicate) for the studied enstatite chondrites is minimum (−0.44 ‰) for Abee (impact-melt breccia) and maximum (+0.16) for St.Marks (EH5). The Ca isotope fractionation between oldhamite (individual mineral grains and leachate) and silicates in Norton County varies from −0.47 ‰ to −0.31 ‰ with an average of −0.41 ‰. These Δ44/40Ca oldhamite-silicate correlate well with previous theoretical calculation and suggests that the oldhamites in Norton County are in isotopic equilibrium with co-existing silicates, and therefore were formed during magmatic processes. However, in enstatite chondrites, the large variation on Δ44/40Ca oldhamite-silicate and its negative correlation with metamorphic temperature reflects the redistribution and equilibration of Ca isotopes during metamorphism. The variable Δ44/40Ca oldhamite-silicate found in unequilibrated chondrites reflect kinetic Ca isotope fractionation between oldhamite and nebular gas and therefore is evidence for the formation of oldhamite by condensation in the solar nebula. [ABSTRACT FROM AUTHOR]

Here, we present a petrographic and microanalytical study of microinclusions in chromite from podiform chromitites hosted by the Sartohay ophiolitic mélange in west Junggar, northwestern China, to investigate the parental magma evolution and chromitite genesis. These silicate inclusions comprise olivine, enstatite, diopside, amphibole, and Na-phlogopite. Their morphological characteristics suggest that most inclusions crystallized directly from the captured melt, with a few anhydrous inclusions (olivines and pyroxenes) as solid silicates trapped during the chromite crystallization. Equilibrium pressure–temperature conditions of coexisting enstatite–diopside inclusions are 8.0–21.6 kbar, and 874–1048 °C. The high Na2O and TiO2 contents of hydrous minerals indicate that the parental magma of chromitites was hydrous and enriched in Mg, Na, Ca, and Ti. The calculated Al2O3 content and FeO/MgO ratio of the parental melts in equilibrium with chromite showed MORB affinity. However, the TiO2 values of parental melts, TiO2 contents of chromite, and estimated fO2 values for chromitites (1.3–2.0 log units above the FMQ buffer) evoked parental MORB-like tholeiitic melts. The composition of olivine inclusion was determined, and it was revealed that the primary melts of the Sartohay podiform chromitites had MgO contents of ~22.7 wt %. This aligns with the observed high magnesian signature in mineral inclusions (Fo = 96–98 in olivine, Mg# = 0.91–0.97 in diopside, and Mg# = 0.92–0.97 in enstatite). We propose that Sartohay podiform chromitites initially formed through the mixing/mingling of primary hydrous Mg-rich melt and the evolved MORB-like melt derived from the melt–peridotite reaction in the upper mantle. In this process, the continuous crystallization of chromite captured micro-silicate mineral inclusions, finally leading to the formation of the Sartohay podiform chromitites. [ABSTRACT FROM AUTHOR]

The occurrence of forsteritic olivine in EH enstatite chondrites is indicative of bulk disequilibrium. In MgO‐rich magmatic systems, forsterite can either crystallize as a liquidus phase or be produced during peritectic melting of enstatite. Because diffusion of divalent cations through forsterite is relatively rapid, it records peak melting (i.e., chondrule‐forming events) and is also sensitive to subsequent metamorphism in the EH chondrite parent body. Here, we report the major and minor element geochemistry of olivine in EH chondrites across petrologic types 3 and 4. In all cases, olivine meets the technical definition of forsterite (>90 mole% Mg2SiO4). For unequilibrated EH chondrites, minor elements identify CaO‐Al2O3‐TiO2‐rich (refractory forsterite), MnO‐rich ("LIME" forsterite), and FeO‐bearing (forsteritic olivine) endmember components, the latter with Cr2O3‐rich and Cr2O3‐poor varieties. At higher petrologic type, minor element concentrations become restricted and compositions approach pure forsterite, while grain sizes reduce strongly with peak metamorphic temperatures. These changes reflect diffusive equilibration with enstatitic groundmass and dissolution reaction with free silica. The global geochemical distribution of forsteritic olivine in EH chondrites is, perhaps unexpectedly, more similar to those in low‐FeO type I chondrules and associated objects in carbonaceous chondrites (CCs), rather than equivalent objects in ordinary (H, L, LL), low‐FeO (or HH), or Kakangari (K) chondrites. Among achondrites, there is similarity between pure forsterite in aubrites and EH4 chondrites arising due to subsolidus equilibration in both settings, while Cr2O3‐poor forsteritic olivine in EH3 and CCs is similar to magnesian xenocrystic olivine in angrites. This might reflect CaO‐rich and SiO2‐poor magmatic sources across multiple early solar system reservoirs. [ABSTRACT FROM AUTHOR]

The giant planets of the Solar System formed on initially compact orbits, which transitioned to the current wider configuration by means of an orbital instability. The timing of that instability is poorly constrained. In this work, we use dynamical simulations to demonstrate that the instability implanted planetesimal fragments from the terrestrial planet region into the asteroid main belt. We use meteorite data to show that the implantation occurred >60 million years (Myr) after the Solar System began to form. Combining this constraint with a previous upper limit derived from JupiterÕs trojan asteroids, we conclude that the orbital instability occurred 60 to 100 Myr after the beginning of Solar System formation. The giant impact that formed the Moon occurred within this range, so it might be related to the giant planet instability. [ABSTRACT FROM AUTHOR]

The anomalous polymict ureilite Almahata Sitta (AhS) fell in 2008 when asteroid 2008 TC3 disintegrated over Sudan and formed a strewn field of disaggregated clasts of various ureilitic and chondritic types. We studied the petrology and oxygen isotope compositions of enstatite meteorite samples from the University of Khartoum (UoK) collection of AhS. In addition, we describe the first bona fide (3.5 mm‐sized) clast of an enstatite chondrite (EC) in a typical polymict ureilite, Northwest Africa (NWA) 10657. We evaluate whether 2008 TC3 and typical polymict ureilites have a common origin, and examine implications for the history of enstatite meteorite asteroids in the solar system. Based on mineralogy, mineral compositions, and textures, the seven AhS EC clasts studied comprise one EHa3 (S151), one ELb3 (AhS 1002), two EHb4‐5 (AhS 2012, AhS 26), two EHb5‐6 or possibly impact melt rocks (AhS 609, AhS 41), and one ELb6‐7 (AhS 17), while the EC clast in NWA 10657 is EHa3. Oxygen isotope compositions analyzed for five of these are similar to those of EC from non‐UoK collections of AhS, and within the range of individual EC meteorites. There are no correlations of oxygen isotope composition with chemical group or subgroup. The EC clasts from the UoK collection show the same large range of types as those from non‐UoK collections of AhS. The enstatite achondrite, AhS 60, is a unique type (not known as an individual meteorite) that has also been found among non‐UoK AhS samples. EC are the most abundant non‐ureilitic clasts in AhS but previously were thought to be absent in typical polymict ureilites, necessitating a distinct origin for AhS. The discovery of an EC in NWA 10657 changes this. We argue that the types of materials in AhS and typical polymict ureilites are essentially similar, indicating a common origin. We elaborate on a model in which AhS and typical polymict ureilites formed in the same regolith on a ureilitic daughter body. Most non‐ureilitic clasts are remnants of impactors implanted at ~50–60 Myr after CAI. Differences in abundances can be explained by the stochastic nature of impactor addition. There is no significant difference between the chemical/petrologic types of EC in polymict ureilites and individual EC meteorites. This implies that fragments of the same populations of EC parent bodies were available as impactors at ~50–60 Myr after CAI and recently. This can be explained if materials excavated from various depths on EC bodies at ~50–60 Myr after CAI were reassembled into mixed layers, leaving relatively large bodies intact to survive 4 billion years. Polymict ureilites record a critical timestep in the collisional and dynamical evolution of the solar system, showing that asteroids that may have accreted at distant locations had migrated to within proximity of one another by 50–60 Myr after CAI, and providing constraints on the dynamical processes that could have caused such migrations. [ABSTRACT FROM AUTHOR]

Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and 29Si, 27Al, and 25Mg solid-state nuclear magnetic resonance (NMR) spectroscopy were used to measure the structure of glassy diopside (CaMgSi2O6), enstatite (MgSiO3), and four (MgO)x(Al2O3)y(SiO2)1−x−y glasses, with x = 0.375 or 0.25 along the 50 mol. % silica tie-line (1 − x − y = 0.5) or with x = 0.3 or 0.2 along the 60 mol. % silica tie-line (1 − x − y = 0.6). The bound coherent neutron scattering length of the isotope 25Mg was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline 25MgO. The diffraction results for the glasses show a broad asymmetric distribution of Mg–O nearest-neighbors with a coordination number of 4.40(4) and 4.46(4) for the diopside and enstatite glasses, respectively. As magnesia is replaced by alumina along a tie-line with 50 or 60 mol. % silica, the Mg–O coordination number increases with the weighted bond distance as less Mg2+ ions adopt a network-modifying role and more of these ions adopt a predominantly charge-compensating role. 25Mg magic angle spinning (MAS) NMR results could not resolve the different coordination environments of Mg2+ under the employed field strength (14.1 T) and spinning rate (20 kHz). The results emphasize the power of neutron diffraction with isotope substitution to provide unambiguous site-specific information on the coordination environment of magnesium in disordered materials. [ABSTRACT FROM AUTHOR]

Synthesized polycrystalline samples composed of enstatite and olivine with different volumetric ratios were deformed in compression under anhydrous conditions in a Paterson gas‐medium apparatus at 1150–1300°C, an oxygen fugacity buffered at Ni/NiO, and confining pressures of 300 or 450 MPa (protoenstatite or orthoenstatite fields). Mechanical data suggest a transition from diffusion to dislocation creep with increasing differential stress for all compositions. Microstructural analyses by optical and scanning electron microscopy reveal well‐mixed aggregates and homogeneous deformation. Crystallographic preferred orientations measured by electron backscatter diffraction are consistent with activation of the slip systems (010)[100] and (010)[001] for olivine and (100)[001] and (010)[001] for enstatite, as expected at these conditions. Nonlinear least‐squares fitting to the full data set from each experiment allowed the determination of dislocation creep flow laws for the different mixtures. The stress exponent is 3.5 for all compositions, and the apparent activation energies increase slightly as a function of enstatite volume fraction. Within the limits of experimental uncertainties, all two‐phase aggregates have strengths that lie between the uniform strain rate (Taylor) and the uniform stress (Sachs) bounds calculated using the dislocation creep flow laws for olivine and enstatite. Calculation of the Taylor and Sachs bounds at strain rate and temperature conditions expected in nature (but not extrapolating in pressure) indicates that using the dislocation creep flow law for monomineralic olivine aggregates provides a good estimate of the viscosity of olivine‐orthopyroxene rocks deforming by dislocation creep in the deeper lithosphere and asthenosphere. Plain Language Summary: The rheology of Earth's upper mantle is generally modeled using mechanical flow laws determined for aggregates composed only of olivine minerals, in spite of the polyphase nature of mantle rocks. In this study, we investigated the effect of phase volume proportions on the high‐temperature deformation properties of aggregates composed of the two most abundant minerals in the upper mantle, olivine and enstatite. The samples were deformed under dry conditions in triaxial compression at 1150–1300°C, under oxygen fugacity fixed at the Ni/NiO solid buffer, and confining pressures of 300 or 450 MPa, at conditions where enstatite has two different crystallographic structures. At both pressures, in the dislocation creep regime, where deformation occurs mostly by the motion of dislocations along slip planes within mineral grains, the strengths of all the two‐phase mixtures lie between the uniform strain rate and the uniform stress bounds, which assume iso‐strain and iso‐stress conditions, respectively, in all the grains comprising each aggregate. Extrapolating these bounds to temperatures and strain rates expected in nature indicates that the viscosity of mantle rocks can be modeled adequately with the dislocation creep flow law for olivine. Key Points: Polycrystalline samples of enstatite and olivine with different volumetric ratios were deformed in compression at high temperatureAll two‐phase aggregates have strengths in dislocation creep that lie between the uniform stress and uniform strain rate boundsIn dislocation creep the flow law for olivine provides a good estimate of the viscosity of olivine‐pyroxene rocks under natural conditions [ABSTRACT FROM AUTHOR]

Mass-independent isotopic anomalies in meteorites are probes to the dynamics and evolution of the protoplanetary disc and the reservoirs from which planetary bodies accreted. Variable Cr nucleosynthetic compositions between meteorite groups are observed but the cause is not well understood. Investigations on presolar carriers in unequilibrated chondrites are thus required to establish these relationships. For that purpose, we analysed the Cr isotope compositions of leachates (stepwise dissolution solutions) of one ordinary chondrite and two enstatite chondrites of EL and EH subgroups previously measured for Nd and Sm isotopes. The leachates of the ordinary chondrite display large variations of their Cr isotope compositions, whereas the leachates of the enstatite chondrites show very limited variations of their nucleosynthetic compositions, confirming other studies. The Cr isotope compositions of leachates of unequilibrated chondrites are significantly modified by thermal processing and aqueous alteration under various conditions. The leachates of the enstatite chondrites are relatively homogeneous for Cr isotope composition, suggesting that presolar carriers of Cr are not stable under very reduced conditions and are likely oxidised phases. After careful examination of the role of parent body processing, we conclude that there is one predominant presolar carrier enriched in 54Cr that produced most of the nucleosynthetic variations observed in leachates. This carrier is likely depleted in the carbonaceous reservoir relative to the non-carbonaceous reservoir. The drastically different isotope compositions of Cr and heavy refractory lithophile elements such as Nd of leachates of chondrites reflect relative preservation biases of their respective presolar carriers, namely a still poorly characterised presolar oxide and silicon carbide (SiC), respectively. [ABSTRACT FROM AUTHOR]

In this work, we investigate macroscopic characteristics, magnetic susceptibility, mineralogy, and mineral composition of Al Haggounia 001. The samples were collected during eight field missions in the period between 2015 and 2019. In the strewn field of about 65 km in length, the specimens are found either on the surface or shallowly buried in loose sediments, which rules out the previous suggestions that this meteorite is a fossil meteorite. Macroscopically, the samples exhibit three major lithologies with various colors, porosities, and distributions of oxidized veins. The data obtained using transmitted and reflected light microscopy, scanning electron microscopy, and electron microprobe analysis confirm the macroscopic observations and show a heterogenous distribution of silicates and metal sulfides. Al Haggounia 001 is composed of enstatite, plagioclase, kamacite, taenite, schreibersite, daubreelite, troilite, graphite, sinoite, and silica polymorphs. We identified a new type of chondrules that are flattened and composed of rods of albite and enstatite, as well as elongated nodules of metal and sulfides, in addition to compression fractures in the form of subparallel veinlets. These features presumably reflect the deformation caused by shock. The magnetic susceptibility of Al Haggounia 001 (4.39 ± 0.20) is much lower than that of usual EH (5.48 ± 0.16) and EL (5.46 ± 0.04) chondrites but is in the range of E finds (5.05 ± 0.43). The thermomagnetic and hysteresis measurements are controlled by type, size, distribution of metal‐sulfide nodules, arrangement of oxyhydroxide veins, and weathering. Al Haggounia 001 is an anomalous meteorite with a polymict nature. It records multiple events revealing its unique origin which expends the groups of enstatite chondrites and provides insights into the complex formation and evolution history of their parent body. [ABSTRACT FROM AUTHOR]

The relationship of mass‐independent stable isotope anomalies with the chemistry of chondritic meteorites provides constraints on mixing and fractionation processes in the early solar nebula. The present study emphasizes the strong correlation of nucleosynthetic isotope variations among ordinary chondrites (OC), enstatite chondrites (EC), Earth, CI‐chondrites, and Ca, Al‐rich inclusions (CAI) in ε50Ti versus ε54Cr space. This correlation indicates variable contamination of chondritic reservoirs with material from a single source providing neutron‐rich nuclei such as 50Ti, 54Cr, and 62Ni. The well‐defined linear relationship of ε50Ti versus ε54Cr indicates that all reservoirs on the correlation line ("chondrite reference line") started with a CI‐chondritic (solar) Cr/Ti ratio, irrespective of the present Cr/Ti ratio of the samples falling on the chondrite reference line. The isotope compositions of carbonaceous chondrites (CC) do not fit the chondrite reference line. Their isotope composition is consistent with a mixture of chondritic meteorites originally falling on the chondrite reference line and volatile element depleted CAIs. However, CC cannot result from addition of CAIs to OC or EC. Neither can OC and EC be produced by loss of refractory components from CI‐meteorites. Also, stable isotopes are inconsistent with OC being derived from EC, and vice versa, by a chemical fractionation process. The enrichment of the Earth in refractory lithophile elements is not the result of addition of a refractory component to a chondritic reservoir. It is rather the result of internal fractionation of a chondritic reservoir. [ABSTRACT FROM AUTHOR]

Here, we present a petrographic and microanalytical study of microinclusions in chromite from podiform chromitites hosted by the Sartohay ophiolitic mélange in west Junggar, northwestern China, to investigate the parental magma evolution and chromitite genesis. These silicate inclusions comprise olivine, enstatite, diopside, amphibole, and Na-phlogopite. Their morphological characteristics suggest that most inclusions crystallized directly from the captured melt, with a few anhydrous inclusions (olivines and pyroxenes) as solid silicates trapped during the chromite crystallization. Equilibrium pressure–temperature conditions of coexisting enstatite–diopside inclusions are 8.0–21.6 kbar, and 874–1048 °C. The high Na2O and TiO2 contents of hydrous minerals indicate that the parental magma of chromitites was hydrous and enriched in Mg, Na, Ca, and Ti. The calculated Al2O3 content and FeO/MgO ratio of the parental melts in equilibrium with chromite showed MORB affinity. However, the TiO2 values of parental melts, TiO2 contents of chromite, and estimated fO2 values for chromitites (1.3–2.0 log units above the FMQ buffer) evoked parental MORB-like tholeiitic melts. The composition of olivine inclusion was determined, and it was revealed that the primary melts of the Sartohay podiform chromitites had MgO contents of ~22.7 wt %. This aligns with the observed high magnesian signature in mineral inclusions (Fo = 96–98 in olivine, Mg# = 0.91–0.97 in diopside, and Mg# = 0.92–0.97 in enstatite). We propose that Sartohay podiform chromitites initially formed through the mixing/mingling of primary hydrous Mg-rich melt and the evolved MORB-like melt derived from the melt–peridotite reaction in the upper mantle. In this process, the continuous crystallization of chromite captured micro-silicate mineral inclusions, finally leading to the formation of the Sartohay podiform chromitites.

The city wall is a military defense building of an ancient city and a unique landscape architecture of a modern country that has extremely important historical, artistic, and scientific values. Most ancient Chinese walls were built of bricks and have been severely damaged and degraded by environmental and human influences. To protect these historical building monuments, it is necessary to determine scientifically the material properties of the bricks used in the ancient walls. In this study, the physical and mechanical properties, chemical element composition, mineral composition, micromorphology, and pore structure of 20 ancient fired clay bricks from four different regions, including white and blue wall bricks from Nanjing, blue wall bricks from Xi'an and Linqing, and the Great Wall bricks from Beijing, were compared using various modern analysis and testing methods. The results show that talc could be one of the raw materials to produce white bricks and the firing temperature of some white bricks could exceed 1200 ℃. The ancient blue bricks were mainly composed of quartz and feldspar, whereas the ancient white bricks were mainly composed of quartz and long prismatic and rod-like enstatite. The solid density and compressive strength of the white bricks were higher than that of the blue bricks. The proportion of pores larger than 10 µm in all ancient bricks is less than 10%. The pores smaller than 0.1 µm is less than 6% at higher firing temperatures. The results of this study can provide scientific guidance for the restoration and conservation of fired clay bricks of ancient city wall.

We report on new trace element analyses of enstatite chondrites (ECs) to clarify their behavior during the metamorphism. During the transition from a type 3 to a type 5 or higher, silicates lose a large portion of their trace elements to sulfides. Our procedure allows us to obtain trace element abundances of the silicate fraction of an EC quite easily. The element patterns of these fractions (especially REE patterns) are quite different for EH and EL chondrites, and are furthermore dependent on the metamorphic grade. This procedure can be usefull to classify meteorites, in particular when the sulfides are altered. Applied to anomalous ECs, it allows direct recognition of the EH affinity of QUE 94204, and suggests that Zakłodzie, NWA 4301, and NWA 4799 derive from the same EH-like body of previously unsampled composition. We have used the concentrations obtained on the silicate fractions of the most metamorphosed chondrites to discuss the chemical characteristics of the primitive mantles of reduced bodies of EH or EL affinity (i.e., after core segregation). Our data indicate that these mantles are very depleted in refractory lithophile elements (RLEs), particularly in rare earth elements (REEs), and notably show significant positive anomalies in Sr, Zr, Hf, and Ti. These estimates imply that the cores contain most of the REEs, U and Th of these bodies. Interestingly, the inferred primitive mantles of these reduced bodies contrast with that of the Earth. If the Earth accreted essentially from ECs, one would expect similar signatures to be preserved, which is not the case. This mismatch can be explained either by a later homogenization of the bulk silicate Earth, or alternatively, that the materials that were accreted were isotopically similar to ECs, but mineralogically different (i.e., oldhamite-free). [ABSTRACT FROM AUTHOR]

Aim of study was to verify the effect of temperature on the pozzolanic reactivity of thermally activated attapulgite and sepiolite samples. Activation temperatures were selected: 650, 700 and 750 °C for attapulgite and 800, 825 and 850 °C for sepiolite. Content of pozzolanic reactive SiO2 and Al2O3 after thermal treatment and the amount of Ca(OH)2 consumed in the pozzolanic reaction were measured. It should be noted that a higher activation temperature improves the reactivity of attapulgite and sepiolite. The upper limit for the increase in the pozzolanic reactivity of these materials is the formation of enstatite and the deactivation of silica. In addition to reactive decomposition products, series of minerals formed in the reactions of attapulgite and sepiolite with impurities present in them are also observed. [ABSTRACT FROM AUTHOR]

Silicon and iron isotope compositions of different physically separated components of enstatite chondrites (EC) were determined in this study to understand the role of nebular and planetary scale events in fractionating Si and Fe isotopes of the terrestrial planet‐forming region. We found that the metal–sulfide nodules of EC are strongly enriched in light Si isotopes (δ30Si ≥ −5.61 ± 0.12‰, 2SD), whereas the δ30Si values of angular metal grains, magnetic, slightly magnetic, and non‐magnetic fractions become progressively heavier, correlating with their Mg# (Mg/(Mg+Fe)). White mineral phases, composed primarily of SiO2 polymorphs, display the heaviest δ30Si of up to +0.23 ± 0.10‰. The data indicate a key role of metal–silicate partitioning on the Si isotope composition of EC. The overall lighter δ30Si of bulk EC compared to other planetary materials can be explained by the enrichment of light Si isotopes in EC metals along with the loss of isotopically heavier forsterite‐rich silicates from the EC‐forming region. In contrast to the large Si isotope heterogeneity, the average Fe isotope composition (δ56Fe) of EC components was found to vary from −0.30 ± 0.08‰ to +0.20 ± 0.04‰. A positive correlation between δ56Fe and Ni/S in the components suggests that the metals are enriched in heavy Fe isotopes whereas sulfides are the principal hosts of light Fe isotopes in the non‐magnetic fractions of EC. Our combined Si and Fe isotope data in different EC components reflect an inverse correlation between δ30Si and δ56Fe, which illustrates that partitioning of Si and Fe among metal, silicate, and sulfidic phases has significantly fractionated Si and Fe isotopes under reduced conditions. Such isotope partitioning must have occurred before the diverse components were mixed to form the EC parent body. Evaluation of diffusion coefficients of Si and Fe in the metal and non‐metallic phases suggests that the Si isotope compositions of the silicate fractions of EC largely preserve information of their nebular processing. On the other hand, the Fe isotopes might have undergone partial or complete re‐equilibration during parent body metamorphism. The relatively uniform δ56Fe among different types of bulk chondrites and the Earth, despite Fe isotope differences among their components, demonstrates that the chondrite parent bodies were not formed by random mixing of chondritic components from different locations in the disk. Instead, the chondrite components mostly originated in the same nebular reservoir and Si and Fe isotopes were fractionated either due to gas–solid interactions and associated changes in physicochemical environment of the nebular reservoir and/or during parent body processing. The heavier Si isotope composition of the bulk silicate Earth may require accretion of chondritic and/or isotopically heavier EC silicates along with cumulation of refractory forsterite‐rich heavier silicates lost from the EC‐forming region to form the silicate reservoir of the Earth. [ABSTRACT FROM AUTHOR]

The presence of amorphous silicate particles in interstellar and circumstellar space has been suggested based on the observation of 9.7 and 18 μ m emission bands. We have successfully synthesized amorphous silicate samples of an enstatite and forsterite composition by the mechanical milling of mixed powder consisting of SiO2–MgO and SiO2–Mg(OH)2 reagent-grade particles under different rotation frequencies and milling times. These two types of starting materials are prepared to study the effect of the OH bond on synthesis and crystallization. The amorphous samples were characterized by X-ray diffraction and infrared spectroscopy. Amorphous samples with enstatite composition are synthesized from both SiO2–MgO and SiO2–Mg(OH)2 at 300 rpm and for 300 hr. Amorphous samples with forsterite composition are synthesized from both SiO2–MgO and SiO2–Mg(OH)2. The samples from SiO2–Mg(OH)2 require 400 rpm and a long milling time of 1600 hr. After crystallization, amorphous samples with an enstatite composition synthesized from SiO2–Mg(OH)2 mainly transform into forsterite with small amounts of amorphous silica SiO2 and enstatite depending on the rotation frequencies and milling time, while those from SiO2–MgO become enstatite. The amorphous samples with a forsterite composition are crystallized to forsterite from both starting materials. The presence of H2O or OH bonds significantly affects the final products after the crystallization of amorphous silicates of enstatite composition. [ABSTRACT FROM AUTHOR]

As the Sun was forming, calcium–aluminum‐rich inclusions (CAIs) were the first rocks to have condensed in the hottest regions of the solar nebula disk. Carbonaceous chondrites (CCs) contain abundant CAIs but are thought to have accreted in the outer Solar System, requiring that CAIs must have been transported outward. Curiously, CAIs are rare in ordinary, enstatite, rumuruti, and kakangari chondrites, non‐carbonaceous chondrites (NCs), that likely formed in the inner Solar System. Thus, CAI abundances and characteristics can provide constraints on the early dynamical evolution of the disk. In this work, we address whether the hypothesis of an early‐formed proto‐Jupiter "opening a gap" in the disk can explain the dichotomy in the relative abundance of CAIs in CC and NC chondrites. We searched 76 NC meteorite sections to find 232 CAIs which have an average apparent diameter of 46 μm and comprise 0.01 area%, about half the size of and ~200 times less abundant than CC CAIs on average. Unlike CC CAIs, only 4% of the NC CAIs contain melilite and most contain alteration features suggesting that NC CAIs underwent pervasive fluid‐assisted thermal metamorphism on asteroidal parent bodies. However, based on NC CAI populations correlating with meteorite metamorphic grade, we argue that disk dynamics is likely the primary reason behind the existence of small (<100 μm) and rare NC CAIs. Our data support astrophysical models which suggest that, after outward transport of CAIs, formation of a gap in the disk trapped CAIs in the outer Solar System. [ABSTRACT FROM AUTHOR]

We studied a thin section of Lewis Cliff (LEW) 87223, an unusual EL3‐related, enstatite chondrite (EC) that has primary and secondary features not observed in other ECs. We studied its metal‐rich nodules, possible shock features, and chondrules, eight of which are Al‐rich chondrules (ARCs). LEW 87223 has petrologic and compositional features similar to EL3s. Enstatite is the dominant mineral; chondrule boundaries are well defined; Si content of metal (0.5–0.6 wt%) is consistent with typical EL3; it has Cr‐bearing troilite, oldhamite, and alabandite; and its O‐isotopic composition is similar to other ECs. However, metal abundance in LEW 87223 (~13 vol%) is slightly higher than in other EL3s and its metal nodules are texturally and mineralogically different from other ECs. Both high and low Ni metals are present, and its alabandite has higher Fe (27.8 wt% Fe) than in other EL3s. Silicates appear darkened in plane polarized light, largely due to reduction of Fe from silicate. A remarkable feature of LEW 87223 is the high abundance of ARCs, which contain Ca‐rich plagioclase and varying amounts of Na‐rich plagioclase along chondrule edges and as veins. This suggests Na metasomatism and the possibility of hydrothermal fluids, potentially related to an impact event. LEW 87223 expands the range of known EC material. It shows that ECs are more diverse and record a wider range of parent body processes than previously known. LEW 87223 is an anomalous EL3, potentially the first member of a new EC group should similar samples be discovered. [ABSTRACT FROM AUTHOR]

Filamentary enstatite crystals, formed by gas–solid condensation in the solar nebula, are found in chondritic porous interplanetary dust particles of probable cometary origin. We measured the oxygen isotopic composition of four filamentary enstatite grains, two whiskers (1.8 μm and 2.3 μm in length) and two ribbons (3.4 μm and 6.1 μm in length), from the giant cluster interplanetary dust particle U2-20 GCP using NanoSIMS ion imaging. These grains represent both the 16O-rich solar (δ 17,18O ≈ - 70 ‰) and 16O-poor planetary (δ 17,18O ≈ 0 ‰) isotope reservoirs. Our measurements provide evidence for very early vaporization of dust-poor and dust-rich regions of the solar nebula, followed by condensation and outward transport of crystalline dust to the comet-forming region very far from the Sun. Similar processes are likely responsible for the crystalline silicates observed in the outer regions of protoplanetary disks elsewhere in the Galaxy. [ABSTRACT FROM AUTHOR]

Recent experiments have suggested that melt flow plays a critical role in the ablation of meteoroids during atmospheric entry. Thus, modeling ablation requires knowledge of the melt properties of meteoritic constituents. These properties, however, are poorly understood and difficult to obtain with experimental techniques at entry conditions. An alternative means of obtaining high-temperature melt properties is through ab initio molecular dynamics (AIMD) simulations. Such simulations are performed here to characterize the melt properties of enstatite ( MgSiO 3), which is prevalent in certain types of chondrites, and its constitutive oxides ( SiO 2 and MgO). The structure, thermodynamic properties (density, bulk modulus, heat capacity, and coefficient of thermal expansion), and transport properties (diffusion and viscosity) are computed across the entire liquid phase and agree well with the limited number of available experiments. The high fidelity AIMD results are compared against less accurate models for melt property determination, which include classical molecular dynamics simulations and empirical mixture rules. Properties obtained from these alternative models generally show large relative errors compared to experiment, with viscosity, in particular, having errors of up to 98%. The present results highlight the potential of AIMD simulations to provide "quantitatively accurate" properties for melts of complex silicates found in meteorites and terrestrial rocks. [ABSTRACT FROM AUTHOR]

Meteoritical Bulletin 110 contains the 2802 meteorites approved by the Nomenclature Committee of the Meteoritical Society in 2021. It includes 10 falls (Arpu Kuilpu, Djadjarm, Glendale, Kindberg, Madura Cave, Motopi Pan, Orconuma, Punggur, Tihigrin, Winchcombe), with 2014 ordinary chondrites (including 1 ungrouped ordinary chondrite), 220 carbonaceous chondrites (including 11 ungrouped), 212 HED achondrites, 69 lunar meteorites, 62 ureilites, 43 iron meteorites, 35 Martian meteorites, 31 Rumuruti chondrites, 27 primitive achondrites, 24 mesosiderites, 19 relict meteorites (all iron meteorites), 15 pallasites, 13 enstatite chondrites, 11 ungrouped achondrites, 7 enstatite achondrites. Of the meteorites classified in 2021, 1270 are from Antarctica, 1049 from Africa, 329 from South America, 123 from Asia, 20 from North America, 6 from Europe, 3 from Oceania, and 2 from unknown locations. [ABSTRACT FROM AUTHOR]

The static wideline and high-resolution magic angle spinning (MAS) 25Mg NMR lineshapes measured for isotopically enriched enstatite and diopside glasses indicate a wide distribution of the electric-field gradient (EFG) components at the 25Mg position caused by disorder. The correct characterization of this distribution requires simulations with special attention paid to the experimental parameters. Here, both the static spectra obtained by wideband excitation and the MAS-NMR spectra obtained via rotor-synchronized Hahn spin echo acquisition were successfully simulated with the Czjzek distribution model, using one consistent set of parameters. Average nuclear electric quadrupole coupling constants near 8 MHz and a distribution width around 4 MHz were obtained for both materials, which suggests that earlier results on these glasses need to be re-examined. The results of this study outline a general strategy for characterizing the local environments of strongly coupled quadrupolar nuclei in amorphous and glassy materials. Despite the discrepancies between the interaction parameters extracted from our data and those published in earlier NMR work, the best fit to the data indicate an average isotropic chemical shift near 13 ppm (vs. aqueous MgCl2 solution) for both the enstatite and diopside glasses. Assuming the applicability of the current database relating the 25Mg chemical shifts with coordination numbers in crystalline compounds, this value suggests that the Mg2+ ions are six-coordinated. This conclusion, however, is based on the simplifying assumption that the 25Mg spectrum comprises a Czjzek distribution centered at a single isotropic chemical shift value and stands in contrast to the results of recent isotope-selective neutron diffraction studies which give an average Mg-O coordination number of 4.4–4.5 for both glasses. However, reasonable fits to the MAS-NMR spectra can also be obtained when constraining the average isotropic chemical shift to 50 ppm, a value typical of four-coordinated Mg. We conclude that multiple Mg sites with different coordination numbers may well be present and that, in the present glasses, 25Mg NMR at typically used spinning rates and magnetic field strengths (20 kHz, 14.1 T) is not capable of resolving them due to excessive broadening by quadrupolar interactions.

Chemical diffusion of Ca has been characterized in natural enstatite under buffered conditions (IW, NNO) and in air. Experiments were conducted using synthesized powder sources, with Ca diffusion profiles measured with Rutherford Backscattering Spectrometry. A variety of sources of diffusant were used to investigate the effects of silica activity and Ca concentration on diffusion. Calcium diffusion appears relatively insensitive to crystallographic orientation and oxygen fugacity under the range of investigated conditions, and also appears little influenced by differences in silica activity and Ca concentration in the diffusant source. For Ca diffusion in a natural enstatite, we obtain the following Arrhenius relation for diffusion over the temperature range 750–1150 °C, D = 1.17 × 10−10exp(−240 ± 10 kJ mol−1/RT) m2sec−1. Calcium diffusion is slower than Mg, Cr and Fe in enstatite, but faster than larger divalent cations Pb and Eu that also are likely to preferentially occupy the M2 site. Calcium diffusion is also faster than that for trivalent REE and tetravalent Ti in enstatite. Calcium diffusivities in enstatite are intermediate between Ca diffusivities in clinopyroxene and olivine, with Ca diffusion in enstatite about 2 orders of magnitude faster than Ca self-diffusion in diopside and 2 orders of magnitude slower than Ca diffusion in olivine. Diffusion parameters obtained from this study were used to develop a simple model for closure temperature of the Ca-in-opx thermometer of Brey and Köhler (1990). By coupling closure temperature and the Ca-in-opx thermometer, it is possible to constrain cooling rates of peridotites and pyroxenites. Applications to peridotites from the Lanzo Massif and the Oman ophiolite are presented. [ABSTRACT FROM AUTHOR]

The origin of major volatiles nitrogen, carbon, hydrogen, and sulfur in planets is critical for understanding planetary accretion, differentiation, and habitability. However, the detailed process for the origin of Earth's major volatiles remains unresolved. Nitrogen shows large isotopic fractionations among geochemical and cosmochemical reservoirs, which could be used to place tight constraints on Earth's volatile accretion process. Here we experimentally determine N-partitioning and -isotopic fractionation between planetary cores and silicate mantles. We show that the core/mantle N-isotopic fractionation factors, ranging from −4‰ to +10‰, are strongly controlled by oxygen fugacity, and the core/mantle N-partitioning is a multi-function of oxygen fugacity, temperature, pressure, and compositions of the core and mantle. After applying N-partitioning and -isotopic fractionation in a planetary accretion and core–mantle differentiation model, we find that the N-budget and -isotopic composition of Earth's crust plus atmosphere, silicate mantle, and the mantle source of oceanic island basalts are best explained by Earth's early accretion of enstatite chondrite-like impactors, followed by accretion of increasingly oxidized impactors and minimal CI chondrite-like materials before and during the Moon-forming giant impact. Such a heterogeneous accretion process can also explain the carbon–hydrogen–sulfur budget in the bulk silicate Earth. The Earth may thus have acquired its major volatile inventory heterogeneously during the main accretion phase. How and when Earth acquired its major volatiles N-C-H-S remains unclear. Here the authors show that Earth may have acquired its major volatiles from both reduced and oxidized impactors before and during the Moon-forming giant impact. [ABSTRACT FROM AUTHOR]

We provide results of a comprehensive mineralogical and microstructural study of relict lherzolites of the main ore field and fresh rocks from a deep structural borehole drilled in the south-eastern part of the Kempirsay massif. Olivine and orthopyroxene from lherzolites contain numerous pieces of evidence of material redistribution at different scales caused mainly by solid-state processes, such as plastic flow of mantle, syntectonic recrystallization, and annealing. The results of deformation-induced processes at the submicron scale are recorded by optical and electronic microscopy. In olivine, the plastic deformation caused segregation of impurities at structural defects. As a result, abundant tiny rods of newly formed Cr-spinels occurred inside its grains. Moreover, in enstatite, deformation caused partial or complete chemical decomposition with exsolution of diopside, pargasite and spinel lamellae up to the formation of a "fibrous" structure. In other cases, it provided partial or complete recrystallization to form new phases of enstatite-2, forsterite, diopside, pargasite, and spinel. Petrographic observations are validated by geochemical data, i.e., regularly decreasing concentrations of minor elements in neoblasts compared to large grains (porphyroclasts). Further redistribution of spinel grains with the formation of chromitite bodies is witnessed by their permanent association with the most mobile phase of the upper mantle, i.e., olivine, which is the only mineral that remains stable under the intense plastic flow. An increased concentration of Cr-spinel grains during formation of massive chromitites could appear under conditions close to pressure sintering, as evidenced by stressed textures of ores and an increased grain size compared to disseminated chromitites. The formation of unique chromitite deposits is associated with integration of numerous disparate podiform bodies into "ore bunches" due to the tectonic impact in the shear-compression regime. This was most likely associated with transition of the rifting (spreading) regime to that of the upper mantle of the fore-arc basin. [ABSTRACT FROM AUTHOR]

Super-Earths and sub-Neptunes are the most common planet types in our galaxy. A subset of these planets is predicted to be water worlds, bodies that are rich in water and poor in hydrogen gas. The interior structures of water worlds have been assumed to consist of water surrounding a rocky mantle and iron core. In small planets, water and rock form distinct layers with limited incorporation of water into silicate phases, but these materials may interact differently during the growth and evolution of water worlds due to greater interior pressures and temperatures. Here, we use density functional molecular dynamics (DFT-MD) simulations to study the miscibility and interactions of enstatite (MgSiO3), a major end-member silicate phase, and water (H2O) at extreme conditions in water world interiors. We explore pressures ranging from 30 to 120 GPa and temperatures from 500 to 8000 K. Our results demonstrate that enstatite and water are miscible in all proportions if the temperature exceeds the melting point of MgSiO3. Furthermore, we performed smoothed particle hydrodynamics simulations to demonstrate that the conditions necessary for rock-water miscibility are reached during giant impacts between water-rich bodies of 0.7–4.7 Earth masses. Our simulations lead to water worlds that include a mixed layer of rock and water. [ABSTRACT FROM AUTHOR]

On October 7, 2008, the asteroid 2008 TC3 exploded as it entered the Earth's atmosphere, producing significant dust (in the atmosphere) and delivering thousands of stones in a strewn field in Sudan, collectively known as the Almahata Sitta (AhS) stones. About 600 fragments were officially recovered in 2008 and 2009. Further rocks were collected since the fall event by local people. From these stones, 249 were classified at the Institut für Planetologie in Münster (MS) known as MS‐xxx or MS‐MU‐xxx AhS subsamples. Most of these rocks are ureilitic in origin (168; 67%): 87 coarse‐grained ureilites, 60 fine‐grained ureilites, 15 ureilites with variable texture/mineralogy, four trachyandesites, and two polymict breccias. We identified 81 non‐ureilitic fragments, corresponding to 33% of the recovered samples studied in Münster. These included chondrites, namely 65 enstatite chondrites (43 EL; 22 EH), 11 ordinary chondrites (OC), one carbonaceous chondrite, and one unique R‐like chondrite. Furthermore, three samples represent a unique type of enstatite achondrite. Since all AhS stones must be regarded as individual specimens independent from each other, the number of fresh ureilite and enstatite chondrite falls in our meteorite collections has been increased by several hundred percent. Overall, the samples weigh between <1 and 250 g and have a mean mass of ~15 g. If we consider—almost 15 years after the fall—the mass calculations, observations during and after the asteroid entered the atmosphere, the mineralogy of the C1 stones AhS 91A and AhS 671, and the experimental work on fitting the asteroid spectrum (e.g., Goodrich et al., 2019; Jenniskens et al., 2010; Shaddad et al., 2010), the main portion of the meteoroid was likely made of the fine‐grained (carbonaceous) dust and was mostly lost in the atmosphere. In particular, the fact that C1 materials were found has important implications for interpreting asteroid 2008 TC3's early spectroscopic results. Goodrich et al. (2019) correctly suggested that if scientists had not recovered the "water‐free" samples (e.g., ureilites, enstatites, and OC) from the AhS strewn field, 2008 TC3 would have been assumed to be a carbonaceous chondrite meteoroid. Considering that the dominating mass of the exploding meteoroid consisted of carbonaceous materials, asteroid 2008 TC3 cannot be classified as a polymict ureilite; consequently, we state that the asteroid was a polymict carbonaceous chondrite breccia, specifically a polymict C1 object that may have formed by late accretion at least 50–100 Ma after calcium–aluminum‐rich inclusions. [ABSTRACT FROM AUTHOR]

Enstatite chondrites are a small clan of meteorites, only ~ 1% out of all meteorite collection. However, they are the most reduced meteorites and have almost identical isotopic compositions to those of the Earth, suggestive of significant contributions to the latter and other terrestrial planets. Enstatite chondrites contain a unique mineral inventory of sulfides of typical lithophile elements, Si-bearing metal, silicide and phosphide, which record the nebular processes and the thermal metamorphism in asteroidal bodies under extremely reducing environments. EH group is mainly characteristic of the higher Si content of metallic Fe–Ni and the higher MnS contents of sulfides than EL group, indicative of a more reducing condition than the latter. However, the fugacity pH2S could be the same in both EH and EL regions, because it was buffered by kamacite and troilite. The majority of sulfides condensed from the nebula, partially enclosing schreibersite micron-spherules formed probably by early melting. Another part of troilite, sphalerite and djerfisherite, intergrown with perryite, were produced via sulfidation of metallic Fe–Ni. Minor exotic components were also found in enstatite chondrites, including Ca-, Al-rich inclusions and FeO-rich silicate clasts. The Ca-, Al-rich inclusions are identical to those in carbonaceous chondrites except for the alteration under reducing environments, and the FeO-rich silicate clasts show reduction reactions, both suggestive of migration of dust in the protoplanetary disk. The highly reducing conditions (as C/O ratios) might be established via repeating evaporation and condensation of water ice and organic matter across the snow line along the protoplanetary disk, but need to find evidence. Another issue is the preservation of submicron-to-micron-sized presolar grains during high-temperature condensation of the major constituent minerals. After accretion, the parent bodies of EH and EL chondrites probably experienced distinct thermal histories, indicated by their distinct petrologic-type distributions and different correlations with the closure temperatures determined by the FeS contents of sulfides in contact with troilite. The composition of (Mg, Mn, Fe)S, a key indicator for condensation and metamorphism of enstatite chondrites. [ABSTRACT FROM AUTHOR]

Scandium (Sc) is used in several modern industrial applications. Recently, significant Sc concentrations (~100 ppm) were reported in some nickel-cobalt lateritic ores, where Sc may be valuably co-produced. However, Sc is typically not included in routine analyses of Ni-Co ores. This contribution examines the relevance of using routinely analysed elements as geochemical proxies for estimating Sc concentration and distribution. Three Ni-Co lateritic deposits from New Caledonia were investigated. In each deposit, Sc is well correlated with Al2O3. The slopes of deposit-scale Sc-Al2O3 regression lines are remarkably controlled by the composition of enstatite from the parent peridotite. In all deposits, maximum Sc enrichment occurs in the yellow limonite, above the highest Ni and Co enrichment zones. Sc- and Al-bearing crystalline goethite is predominant in the oxide-rich zones, though Sc shows a higher affinity for amorphous iron oxides than Al. We propose that, in already assayed Ni-Co lateritic ores, the concentration and distribution of Sc can be estimated from that of Al. Deposit-scale Sc-Al2O3 correlations may be determined after analysing a limited number of spatially and chemically representative samples. Therefore, mining operators may get a first-order evaluation of the Sc potential resource in Ni-Co lateritic deposits at low additional costs. [ABSTRACT FROM AUTHOR]

The melting behavior of Platreef and UG–2 platinum group metal (PGM) concentrates was studied under conditions typically found in the black top of PGM smelters. In order to understand how the phase changes influence the separation between matte and slag, the concentrates were characterized before and after firing at eight temperatures from 800°C to 1480°C. The PGM concentrates were isothermally heated in either silica (Platreef) or magnesia crucibles (UG–2), which in turn were sealed in steel capsules under argon atmosphere. This configuration prevented the escape of sulfur–containing gases during the experiments. Observed phase relations were compared against phase relations predicted by FactSage® under oxygen partial pressures in the range of 10–18 to 10–9 bar and sulfur partial pressures in the range of 10–9 to 10–3.5 bar. The results showed the effective separation of matte from the gangue minerals at sub–liquidus temperatures of the gangue (1480°C for UG–2 concentrate, 1400°C and 1480°C for Platreef concentrate). The PGM concentrates did not sinter at low temperatures (800–1100°C); however, from 1200°C the formation of a liquid phase promoted liquid phase sintering. The collection of matte in a button at the bottom of the crucible was facilitated by the formation of a continuous liquid phase in the sintered concentrate, through which the matte droplets could descend. This occurred after the main gangue phase, enstatite, melted incongruently. [ABSTRACT FROM AUTHOR]

The Central Alpine lower crustal migmatitic Gruf complex was exhumed in contact to the greenschist-grade Chiavenna ophiolite and gneissic Tambo nappe leading to a lateral gradient of ~ 70 °C/km within the ophiolite. The 14 km long, E-W striking subvertical contact now bridges metamorphic conditions of ~ 730 °C, 6.6 kbar in the migmatitic gneisses and ~ 500 °C, 4.2 kbar in the serpentinites and Tambo schists 2–4 km north of the contact. An obvious fault, mylonite or highly sheared rock that could accommodate the ~ 8.5 km vertical displacement is not present. Instead, more than half of the movement was accommodated in a 0.2–1.2 km thick orthogneiss of the Gruf complex that was heterogeneously molten. Discrete bands with high melt fractions (45–65%) now contain variably stretched enclaves of the adjacent MOR-derived amphibolite. In turn, the adjacent amphibolites exhibit tonalitic in-situ leucosomes and dikes i.e., were partially molten. The H2O necessary for fluid-assisted melting of the orthogneiss and amphibolites was likely derived from the tectonic contact metamorphism of the Chiavenna serpentinites, at the contact now in enstatite + olivine-grade. U–Pb dating of zircons shows that partial melting and diking occurred at 29.0–31.5 Ma, concomitant with the calc-alkaline Bergell batholith that intruded the Gruf. The major driving forces of exhumation were hence the strong regional North–South shortening in the Alpine collisional belt and the buoyancy provided by the Bergell magma. The fluids available through tectonic contact metamorphism led to self-enhanced magmatic weakening and concentration of movement in an orthogneiss, where melt-rich bands provided a low friction environment. Continuous heating of the originally greenschist Chiavenna ophiolite and Tambo gneisses + schists by the migmatitic Gruf complex during differential uplift explains the skewed temperature profile, with intensive contact heating in the ophiolite but little cooling in the portion of the now-exposed Gruf complex. [ABSTRACT FROM AUTHOR]

Values of Fe3+/ ΣFe (ΣFe = Fe3+ + Fe2+) were determined for six (6) pyroxenes, (five (5) diopsides and one (1) enstatite), using the single dissolution technique of Fritz and Popp, 1985 (FP85). These same pyroxenes were analyzed with the electron microprobe (EMP), and values of Fe3+/ΣFe were determined using charge balance from average EMP compositions. Typically, these averages were based on thirty (30) analyses on multiple grains of the same sample, although some pyroxenes were characterized with as few as 9 and as many as 120 analyses. Differences between average values of Fe3+/ΣFe determined using the two methods were ≤ 0.02 for pyroxenes with Fe-contents >9 wt% FeO T (all Fe as FeO T). Pyroxenes with lower Fe contents of approximately 4 to 6 wt% FeO T exhibit differences that fall between 0.02 and 0.06. One pyroxene, with the lowest Fe-content (1.79 wt% FeO T ; 0.055 atoms per formula unit or apfu), exhibits the largest difference Fe3+/ ΣFe difference between EMP and FP85 of 0.14. Values of the standard deviation (1σ), based on average values of Fe3+/ ΣFe (EMP), range from 0.03 to 0.22, which are also inversely correlated to the Fe content. For pyroxenes with FeO T > 4.0 wt%, and with compositions similar to those examined in this study, it is possible to use charge balance to determine values of Fe3+/ΣFe(EMP) to better than ±0.07. • Pyroxene stoichiometries, calculated from electron microprobe (EMP) analyses, yield values of Fe3+/SFe (charge balance). • Fe3+/SFe (EMP) for 6 pyroxenes (5 diopsides and 1 enstatite) range from 0.84 ±0.22 to 0.17 ±0.04 (1s). • The precision (1s) is sensitive to Fe content, with 1s ≤0.05 for pyroxenes with > 6 wt% FeO T. • Values of Fe3+/SFe, determined independently, agree with Fe3+/SFe(EMP) to within 0.07 for pyroxenes with > 4 wt% FeO T. • Change balance should, therefore, yield useful values of Fe3+/SFe for a variety of natural pyroxenes. [ABSTRACT FROM AUTHOR]

The reflectance spectra of synthetic oldhamite (CaS), synthetic enstatite (Mg 2 Si 2 O 6), and their mixtures have been studied in the spectral range from 0.3 μm to 16 μm. The spectrum of enstatite is very bright, with a steep slope in the ultraviolet (UV) and an almost neutral slope in the visible (VIS) and near-infrared (NIR). The mid-infrared (MIR) region is characterized by the Christiansen feature, Reststrahlen bands and the Transparency feature. The oldhamite spectrum shows a red slope in the UV and VIS and an absorption band at 0.41 μm. The absorption band has a relative depth of 11.4%. In the MIR, the oldhamite spectrum is much brighter than the enstatite spectrum and shows several broad absorption bands. The spectra of the mixtures show an intermediate behavior between the two endmembers. The absorption band at 0.41 μm is visible in the spectra of all mixtures, even in the spectrum of the mixture with only 1 vol% oldhamite. In the MIR, the spectra of the mixtures with ≤10 vol% oldhamite are very similar to the spectrum of pure enstatite. Changes in the spectral characteristics such as reflectance or band depths do not follow simple linear trends but show two distinct trends: One for mixtures with ≤10 vol% oldhamite and one for mixtures with ≥20 vol% oldhamite. Changes occur significantly faster in the spectra of mixtures with ≤10 vol% than in those with ≥20 vol% oldhamite. Reflectance spectra of the E[II]-type asteroid 2867 Šteins are flat and almost featureless but show an absorption band at 0.49 μm, which is attributed to oldhamite. Comparison of the laboratory spectra in the VIS and MIR with spectra of Šteins gives an upper limit for the oldhamite content on its surface of 40 %vol. Hence, Šteins probably consists of aubrite-like material with virtually FeO-free enstatite as the major constituent and an oldhamite abundance of <40 vol%. Šteins and other E[II]-type asteroids likely formed through igneous processes on a larger now destroyed body, where an immiscible CaS-melt formed within a silicate melt. The surface of Mercury is also linked to FeO-poor silicates like enstatite. Oldhamite and other sulfides are linked to the formation of hollows on Mercury. Mixtures of enstatite and oldhamite could therefore serve as suitable model analog for the surface of Mercury. Contrasting trends at ∼7–8.5 μm in the MIR reflectance spectra of oldhamite and enstatite could be used as an indicator for the presence of oldhamite in spectral data that will be collected by the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument onboard the ESA/JAXA BepiColombo mission to Mercury. • VIS and IR reflectance spectra of mixtures of enstatite and oldhamite. • Small amounts of oldhamite are detectable in the mixtures' spectra in the visible. • Upper limit of the oldhamite amount on the surface of asteroid Šteins of ∼40 vol%. • Helpful for detection of oldhamite in future spectral data from Mercury. [ABSTRACT FROM AUTHOR]

The article discusses the inclusions and spectroscopic features of gem-quality yellowish green enstatite from the enstatite-ferrolite series in the clinopyroxene subgroup of the pyroxene group. Also cited are the main source countries of the gemstones, namely, Sri Lanka, Myanmar and Tanzania, and the yellowish enstatite samples analyzed by the GIT Gem Testing Laboratory (GIT-GTL).

We have determined rare-earth element (REE) abundances in oldhamites (CaS) from 13 unequilibrated and equilibrated enstatite chondrites (5 EH and 8 EL) and in a few enstatites by in situ, laser ablation ICP-MS. In EH chondrites, oldhamite REE patterns vary from the most primitive petrographic types (EH3) to the most metamorphosed types (EH5). In EH3, CI-normalized REE patterns are convex downward with strong positive Eu and Yb anomalies, whereas EH5 display flat patterns with enrichments reaching about 80 times CI abundances. The positive anomalies of Eu and Yb found in oldhamites of primitive EH chondrites indicate that they represent the condensation of a residual gas fraction, in a manner similar to fine-grained CAIs of carbonaceous chondrites. The early condensate may have been preserved in the matrix of unequilibrated EH. Equilibrated EH oldhamite patterns may result from metamorphic evolution and REE redistribution on the EH parent body. On the contrary, all the oldhamites from EL chondrites (EL3 to EL6) display a single kind of patterns, which is convex upward and is about 100 times enriched relative to CI, with a negative Eu anomaly. In addition, the EL pattern is similar to that of oldhamites from aubrites (enstatite achondrites). The latter observation suggests that oldhamites of all EL metamorphic types (including primitive ones) bear the signature of a magmatic event accompanied by FeS loss as vapor, prior to the assembly of the EL parent body. Given the difficulty of obtaining precise ages on enstatite chondrites, it is not possible to discuss the chronology of the events recorded by the oldhamite REE patterns. [ABSTRACT FROM AUTHOR]

New 187Re-187Os, 87Rb-87Sr, triple O-isotope isotope, bulk rock highly siderophile- (HSE: Os, Ir, Ru, Pt, Pd, Re), major- and trace-element abundance data are reported for a variety of carbonaceous, ordinary and enstatite chondrite meteorites. In addition, new mineral chemical data are reported for the Chelyabinsk LL5 ordinary chondrite fall for comparison with existing chondrite data and to investigate element sequestration into metal and mineral phases within some chondrites. The focus of the study is to link the variations observed in the HSE abundances and Re-Os isotopes with other isotopic and elemental data to explore the relative roles of sample sizes, terrestrial alteration and parent body processes more fully on chondrite meteorite compositions. Trace element variations in Chelyabinsk silicate, oxide and metal grains highlight the importance of geochemical heterogeneity imparted by mineralogical variations and mode effects, as well as sample size. Using a range of sample powder aliquot sizes, it is possible to show that this becomes significant for the HSE at <0.1 g. Variations in high field strength elements relative abundances (HFSE: Ti, Zr, Nb, Ta, Hf) are also identified within individual aliquots of carbonaceous chondrite Ivuna, emphasizing the importance of complete dissolution of refractory phases. The range of fall and find meteorites examined here demonstrates that terrestrial alteration effects revealed for trace elements (e.g., Ba, U, Sr) do not correlate particularly well with Re/Os variations. Instead, the Re/Os ratios of carbonaceous chondrites are susceptible to disturbance, more so than indicated by incompatible trace element systematics, with the Murchison CM2 carbonaceous chondrite showing significant Re/Os fractionation between sample aliquots. For sample aliquots measured that do not show significant mode or terrestrial alteration effects, parent body processes appear to be largely restricted to thermal metamorphism and dehydration. Including data for this study, the combined published dataset for Re-Os isotope and HSE abundances now extends to 33 ordinary, 39 carbonaceous, 27 enstatite and 6 Rumuruti chondrites. The range in absolute HSE abundances among these meteorite groups is ∼30%, with all chondrites having, within uncertainties, the same average Os, Ir, Ru, Pt and Pd abundances. Notably, carbonaceous chondrites have long-term Re/Os ∼ 8% lower than for the other chondrite groups. If chondrite groups are representative of early planetary feedstocks, then the measured 187Os/188Os of ordinary chondrites make them a close match to the composition of the bulk silicate Earth. Assuming ∼0.5% late accretion of ordinary chondrites to Earth, this would result in a long-term Rb/Sr ratio ∼0.6% higher than from late accretion of carbonaceous chondrites, indicating that ordinary chondrites are a potentially attractive source for moderately volatile enrichment. [ABSTRACT FROM AUTHOR]

Porous forsterite-spinel-periclase ceramics with low thermal conductivity were synthesized via a transient liquid phase diffusion process by using pre-synthesized pellets and fused magnesia powder. The effects of sintering temperature on the pore formation, phase composition, sintering behavior, and properties of the resulting porous ceramics were investigated. The pre-synthesized pellets had a porous structure and contained a large amount of cordierite and enstatite. During the sintering progress, the pellets were converted into a transient liquid phase, which diffused into the solid MgO matrix. The liquid phase diffusion reaction promoted forsterite and spinel formation, which resulted in the in-situ formation of large pores. At elevated temperatures, the liquid phase disappeared and a large number of well-developed grains were simultaneously precipitated from the liquid phase. Porous ceramics with thermal conductivities of 0.42–0.48 W/(m·K) and refractoriness under load values of 1588 °C and 1624 °C were obtained after sintering at 1600 °C for 3 h. [ABSTRACT FROM AUTHOR]

Upper: Giant impact (Courtesy NASA/JPL-Caltech); chondrule, majorite in shocked enstatite (Courtesy Miyahara); Lower: Collision of planetesimals (Courtesy NASA/JPL-Caltech); Raman mapping of wadsleyite and ringwoodite in Peace River L6 (Courtesy Miyahara and El Goresy). [ABSTRACT FROM AUTHOR]

Mixed phase materials in the quasi binary diopside (CaMgSi 2 O 6) – molybdite (MoO 3) system were synthesized by a precipitation method. Materials were fabricated with diopside to molybdite ratios of 1:0, 10:1, 5:1, 2:1 and 1:1. XRD, SEM and EDS results show that alongside the initial diopside phase, phases such as calcium molybdate CaMoO 4 , rod-like enstatite MgSiO 3 and cristobalite SiO 2 formed as the molybdite content increased, and diopside was entirely absent at the highest molybdite content. At lower Mo content, mixed phase materials showed higher hardness and slower biodegradation in SBF relative to pristine diopside, while maintaining reasonable hydroxyapatite (HAp) formation capability. In contrast, materials with higher molybdite content exhibited lower hardness and bioactivity. The variation in the mechanical and bioactive performance could be attributed to the presence of bulk CaMoO 4 , acting as a reinforcement, and rod-like MgSiO 3 with a highly porous and fragile structure. The trend of hardness is not consistent to the proportion of the component phases could be attributed to morphologies, interfaces, and densities of the samples. Both of secondary phases had poorer HAp deposition compared to pure diopside, indicating the MoO 3 addition lowered mixed phase CaMgSi 2 O 6 – MoO 3 bioceramics' ability to form Hap. The results suggest that moderate addition of molybdite to diopside would be an effective pathway towards crystalline bioceramics with enhanced performance. [ABSTRACT FROM AUTHOR]