Meteoritic Minerals Research Articles

The Borodino meteorite: evolution on parent body

The article discusses the results of a mineralogical and petrographic study of the Borodino meteorite (H5). For the first time, meteorite minerals are described and their chemical compositions are given. The following were found in the Borodino meteorite: olivine (Fa 18.16±1.15), low-Ca pyroxene – (clino)enstatite (En 81.37±1.73, Wo 1.18±0.31), high-Ca pyroxene – augite (En 57.23±1.57, Wo 39.38±2.68), diopside (En 51, Wo 45), pigeonite (En 69, Wo 6), plagioclases – oligoclase (An 12.16±1.24, Or 5.68±2.12), andesine (An 48.23±1.84, Or 1.23±0.12), anorthoclase (An 0, Or 36) and sanidine (An 0, Or 40.00±1.1), and weakly crystallized glasses of feldspathic composition, merillite and chrome spinel. The data obtained made it possible to estimate the degree of terrestrial weathering of the meteorite as W0 and the stage of impact metamorphism (S1-2), which suggests good preservation of the meteorite material. The composition of olivine and chrome spinel, determined using the EPMA method, was used to estimate the peak temperature of thermal metamorphism at 720°C, which falls within the temperature range (670–740°C) characteristic of petrological type 5 chondrites. The presence of high-Ca pyroxenes, large grains of Ca–Na–Mg phosphates and chromite-pigeonite aggregates in the meteorite matrix indicate prolonged heating of the material.

Phosphates on Mars and Their Importance as Igneous, Aqueous, and Astrobiological Indicators

This paper reviews the phosphate phases in meteorites and those measured by landed spacecraft, what they reveal about past igneous and aqueous conditions on Mars, and important implications for potential prebiotic chemistry, past habitability, and potential biosignatures that could be detected in samples returned from Mars. A review of the 378 martian meteorites as of 2023 indicate that of the two most common phosphate minerals in Mars meteorites, merrillite and apatites, the apatite composition is largely F- and Cl-rich, with shergottites containing more OH. The phosphate concentrations examined across multiple missions show a relatively narrow range of phosphate, with higher concentrations observed in the Mount Sharp Group in Gale crater and Wishstone at Gusev crater and lower concentrations observed at Jezero crater floor and Jezero fan. Possible secondary phosphates detected on Mars, including Fe phosphates at Jezero crater and Gusev crater and Ca- and Al-bearing secondary phosphates, temperatures of formation of secondary phases and their dissolution rates and solubilities are reviewed and summarized. Despite this wealth of information about phosphates on Mars, due to their fine scale and relatively low concentrations, Mars Sample Return is needed to better understand phosphate and its implications for the igneous, aqueous, and astrobiological history of Mars.

Metasomatism is a source of methane on Mars

The abundance of inactive Martian volcanic centres suggests that early Mars was more volcanically active than today. On Earth, volcanic degassing releases climate-forcing gases such as H2O, SO2, and CO2 into the atmosphere. On Mars, the volcanic carbon is likely to be more methane-rich than on Earth because the interior is, and was, more reducing than the present-day Terrestrial upper mantle. The reports of reduced carbon associated with high-temperature minerals in Martian igneous meteorites back up this assertion. Here, we undertake irreversible reaction path models of the fluid-rock interaction to predict carbon speciation in magmatic fluids at the Martian crust-mantle boundary. We find methane is a major carbon species between 300 and 800 °C where logfO2 is set at the Fayalite = Magnetite + Quartz redox buffer reaction (FMQ). When logfO2 is below FMQ, methane is dominant across all temperatures investigated (300–800 °C). Moreover, ultramafic rocks produce more methane than mafic lithologies. The cooling of magmatic bodies leads to the release of a fluid phase, which serves as a medium within which methane is formed at high temperatures and transported. Metasomatic methane is, therefore, a source of reduced carbonaceous gases to the early Martian atmosphere and, fundamentally, for all telluric planets, moons, and exoplanets with Mars-like low logfO2 interiors.

Mapping the redox state of the young Solar System using ytterbium valence state

We have determined the valence state of Ytterbium (Yb) in a collection of meteorites covering 4–5 orders of magnitude in oxygen fugacity (fO2) by X-ray absorption near-edge structure (XANES) spectroscopy at the Yb L2 edge. In the studied meteorite minerals, Yb abundance was between 1 and 30 ppm. The data were obtained from merrillite grains (theoretical formula Ca18Na2Mg2(PO4)14) from two equilibrated ordinary chondrites (one H6 and one LL6), on oldhamite grains (theoretical formula CaS) from three EH enstatite chondrites (from EH3 to EH5) and four EL enstatite chondrites (from EL3 to EL6), on one merrilite grain and one stanfieldite grain (theoretical formula Ca4(Mg,Fe,Mn)5(PO4)6) from a pallasite, on merrillite grains from a eucrite, and in a phosphorous-bearing phase from an ungrouped primitive achondrite (NWA 11119). The obtained Yb XANES spectra were compared to those measured in terrestrial apatites (containing 17–79 ppm Yb) and in synthetic materials (metallic Yb, YbS, Yb2S3, Yb2O3). In terrestrial apatites, as well as in ordinary chondrites, in the eucrite, in the pallasite, and in the ungrouped achondrite NWA 11119, Yb is present as Yb3+ only. In enstatite chondrites, about half of the Yb in CaS is in the Yb2+ form and the fraction of Yb2+ may be slightly higher in EH compared to EL. It appears that Yb redox state can be used to build a redox scale for the most reduced objects of the Solar System as shown by this slight difference between EH and EL. However, the absence of a strong difference in Yb redox state between EH and EL chondrites suggests that the observed difference in Yb abundance anomalies in oldhamites found between EH and EL is not due to oxygen fugacity prevailing during parent-body equilibration but rather to fractionation related to volatility.

Irradiation induced mineral changes of NWA10580 meteorite determined by infrared analysis

Context. Identifying minerals on asteroid surfaces is difficult as space weathering modifies the minerals’ infrared spectra. This should be better understood for proper interpretation. Aims. We simulated the space weathering effects on a meteorite and recorded the alterations of the crystalline structure, such as the change in peak positions and full width at half maximum values. Methods. We used proton irradiation to simulate the effects of solar wind on a sample of NWA 10580 CO3 chondrite meteorites. After irradiation in three gradually increased steps with 1 keV ion energy, we used infrared microscopic reflectance and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to identify and understand the consequences of irradiation. Results. We find negative peak shifts after the first and second irradiations at pyroxene and feldspar minerals, similarly to the literature, and this shift was attributed to Mg loss. However, after the third irradiation a positive change in values in wavenumber emerged for silicates, which could come from the distortion of SiO4 tetrahedra, resembling shock deformation. The full width at half maximum values of major bands show a positive (increasing) trend after irradiations in the case of feldspars, using IR reflection measurements. Comparing DRIFTS and reflection infrared data, the peak positions of major mineral bands were at similar wavenumbers, but differences can be observed in minor bands. Conclusions. We measured the spectral changes of meteorite minerals after high doses of proton irradiation for several minerals. We show the first of these measurements for feldspars; previous works only presented pyroxene, olivine, and phyllosilicates.

Oxygen Isotope Fractionation Due to Non-Thermal Escape of Hot O from the Atmosphere of Mars

Secondary minerals in SNC meteorites from Mars exhibit O isotope ratios believed to be consistent with the non-thermal escape of O from the atmosphere. The primary source of the non-thermal O is the dissociative- recombination of O2+ in the ionosphere. I present here the results of a model that accounts for the probability of escape of non-thermal O isotopes due to collisions with overlying CO2, combined with a model for Rayleigh fractionation of the atmosphere remaining as a result of O escape. Previous analyses of MAVEN number density data have shown a strong variability with latitude and season of the heights of the homopause and exobase, with a mean homopause at 110 km and a mean difference of about 60 km. Rayleigh model results demonstrate a dependence on homopause height and on temperature profile and require a more accurate calculation of fractionation factors for the Rayleigh equation. Isothermal temperature profiles yield much smaller variation in 17O with homopause height. These results demonstrate the need for a careful assessment of O isotope enrichment due to non-thermal escape both for the modern atmosphere and for the evolution of the atmosphere over the age of the planet.

Revisiting Néel 60 years on: The magnetic anisotropy of L10 FeNi (tetrataenite)

The magnetocrystalline anisotropy energy of atomically ordered L10 FeNi (the meteoritic mineral tetrataenite) is studied within a first-principles electronic structure framework. Two compositions are examined: equiatomic Fe0.5Ni0.5 and an Fe-rich composition, Fe0.56Ni0.44. It is confirmed that, for the single crystals modeled in this work, the leading-order anisotropy coefficient K1 dominates the higher-order coefficients K2 and K3. To enable comparison with experiment, the effects of both imperfect atomic long-range order and finite temperature are included. While our computational results initially appear to undershoot the measured experimental values for this system, careful scrutiny of the original analysis due to Néel et al. [J. Appl. Phys. 35, 873 (1964)] suggests that our computed value of K1 is, in fact, consistent with experimental values, and that the noted discrepancy has its origins in the nanoscale polycrystalline, multivariant nature of experimental samples, that yields much larger values of K2 and K3 than expected a priori. These results provide fresh insight into the existing discrepancies in the literature regarding the value of tetrataenite’s uniaxial magnetocrystalline anisotropy in both natural and synthetic samples.

Advances in Analysis of the Fe-Ni-Co Alloy and Iron-Bearing Minerals in Meteorites by Mössbauer Spectroscopy with a High Velocity Resolution

Meteorites are the space messengers bringing us the unique information about the Solar System formation and evolution as well as about the effects of various extreme space conditions on meteorites and their parent bodies. The main iron-bearing compounds in meteorites are Fe-Ni-Co alloy, olivine (Fe, Mg)2SiO4, orthopyroxene (Fe, Mg)SiO3, clinopyroxene (Ca, Fe, Mg)SiO3, troilite FeS, chromite FeCr2O4, hercynite FeAl2O4, ilmenite FeTiO3, daubréelite FeCr2S4, schreibersite (Fe, Ni)3P and some other compounds. Therefore, 57Fe Mössbauer spectroscopy was successfully applied for the analyses of various meteorites for about 60 years of experience. The development of Mössbauer spectrometers with a high velocity resolution, i.e., with a high discretization of the velocity reference signal up to 212, provides much better adjustment to resonance and significantly increases the spectra quality and analytical possibilities of Mössbauer spectroscopy. In fact, this permits us to decompose the complex Mössbauer spectra of meteorites using the larger number of spectral components related to reliable compounds in comparison with the results obtained using conventional Mössbauer spectrometers with discretization of the velocity reference signal up to 29. In the present review we consider the results and advances of various meteorites analyses by means of Mössbauer spectroscopy with a high velocity resolution.

Degassing of early-formed planetesimals restricted water delivery to Earth.

The timing of delivery and the types of body that contributed volatiles to the terrestrial planets remain highly debated1,2. For example, it is unknown if differentiated bodies, such as that responsible for the Moon-forming giant impact, could have delivered substantial volatiles3,4 or if smaller, undifferentiated objects were more probable vehicles of water delivery5-7. Here we show that the water contents of minerals in achondrite meteorites (mantlesorcrusts of differentiated planetesimals) from both the inner and outer portions of the early Solar System are ≤2 μg g-1 H2O. These are among the lowest values ever reported for extraterrestrial minerals. Our results demonstrate that differentiated planetesimals efficiently degassed before or during melting. This finding implies that substantial amounts of water could only have been delivered to Earth by means of unmelted material.

Formation of mixed-layer sulfide-hydroxide minerals from the Tochilinite-Valleriite group during experimental serpentinization of olivine

Abstract We report the formation of minerals from the tochilinite-valleriite group (TVG) during laboratory serpentinization experiments conducted at 300 and 328 °C. Minerals in the TVG are composed of a mixture of sulfide and hydroxide layers that can contain variable proportions of Fe, Mg, Cu, Ni, and other cations in both layers. Members of this group have been observed as accessory minerals in several serpentinites, and have also been observed in association with serpentine minerals in meteorites. To our knowledge, however, TVG minerals have not previously been identified as reaction products during laboratory simulation of serpentinization. The serpentinization experiments reacted olivine with artificial seawater containing 34S-labeled sulfate, with a small amount of solid FeS also added to the 300 °C experiment. In both experiments, the predominant reaction products were chrysotile serpentine, brucite, and magnetite. At 300 °C, these major products were accompanied by trace amounts of the Ni-bearing TVG member haapalaite, Ni,Fe-sulfide (likely pentlandite), and anhydrite. At 328 °C, valleriite occurs rather than haapalaite and the accompanying Ni,Fe-sulfide is proportionally more enriched in Ni. Reduction of sulfate by H2 produced during serpentinization evidently provided a source of reduced S that contributed to formation of the TVG minerals and Ni,Fe-sulfides. The results provide new constraints on the conditions that allow precipitation of tochilinite-valleriite group minerals in natural serpentinites.

CaCO3 Polymorphs as Mineral Catalysts for Prebiotic Phosphorylation of Uridine

AbstractEstablishing plausible routes for the abiotic formation of nucleotides is a challenging problem because the phosphorylation of organic molecules is thermodynamically unfavorable in water, and because common phosphorous‐containing minerals such as apatite are highly insoluble. Reactions of reduced phases such as the meteoritic mineral schreibersite with ammonia containing solutions can form stable amino‐derivatives of phosphates/phosphite, and carbonate‐rich lakes have been suggested as environments where phosphate species and organic molecules could accumulate in significant abundances, thus promoting an ideal environment for abiotic phosphorylation. This work reports the catalytic properties of three CaCO3 polymorphs—calcite, aragonite, and vaterite—on diamidophosphate (DAP)‐induced phosphorylation of the uridine nucleoside during a 24‐hr dry‐down reaction. It is shown that the phosphorylation reaction is accelerated in solutions containing CaCO3 compared to those with no mineral present. For un‐buffered solutions with no mineral present, the primary products formed are uridine monophosphates (UMPs), with yields making up 22.3 ± 3.9% of the total detected species, while solutions containing calcite and aragonite formed primarily UMP dimers (yields of 15.3 ± 1.1% and 14.8 ± 1.3%, respectively). Vaterite showed a strong preference for forming cyclic UMP (cUMP) (26.3 ± 0.3% yield), and no higher order polymers were observed using any carbonate mineral. Reactions containing CaSO4·2H2O (gypsum) showed a preference for forming cUMP, though not as strong as vaterite, while those containing CaCl2 (calcium chloride) and CaWO4 (scheelite) did not yield any phosphorylated products other than UMPs. These results suggest that CaCO3 minerals could have played an important role in facilitating prebiotic phosphorylation in aqueous environments that undergo drying cycles.

Review of meteorite irradiation tests to support next C-type asteroid missions

ABSTRACT Effect of space weathering of airless asteroids could be better understood by artificial irradiation tests on meteorites in laboratories. This work surveys the infrared and Raman analysis based interpretation of simulated charged particle irradiation tests in order to better understand near-future observational possibilities of asteroid visiting missions and also to support the planning of next missions and directions of detector improvement. Recent works properly targeted different meteors and meteor relevant minerals, evaluating bulk meteorite spectra, during the irradiation tests. He+, (Ne+, Kr+), and Ar+ ions were used with fluxes characteristic for inner planetary system solar wind, considering 1–10 million yr exposure durations. Although main meteorite minerals were irradiated and analysed, one missing aspect is that only bulk analysis have been done, not minerals separately in their original embedded context. Some Earth based mineral references were also analysed; however, they might not necessarily behave similar to the same type of reference minerals and irradiation effect is poorly known for feldspar, troilite, and magnetite. Darkening should be also further analysed for separate minerals too, together with the record of peak shape and position changes. Infrared ATR analysis might still provide such data in the future using the recently emerged technology, as well as Raman analysis – however for flyby missions’ infrared is the useful method while Raman can be used only at in situ missions. The overview including the tables to support the identification of specific missing information related gaps in our current knowledge and directions for future research.

Results of an Eight-Year Extraction of Phosphorus Minerals within the Seymchan Meteorite.

Simple SummaryPhosphorus (P) is essential to life in the form of various phosphate esters that make up DNA, RNA and other cellular structures. It mainly exists in the form of phosphate. However, other reduced-oxidation-state P compounds have also been found in natural waters, in living organisms, and in natural glasses formed by lightning called fulgurites. Iron meteorites often bear a P mineral, schreibersite, which corrodes in water to produce various P species including reduced-oxidation-state compounds such as phosphite. This form of natural P is reactive and unstable as ultimately the phosphides and phosphites convert into phosphate, the most stable form of P on an oxidizing world. Previous analyses of 3.5 billion rocks identified various P species including phosphite revealing that phosphite was present on the early Earth and, despite its reactivity, it was stable under geologic timescales. In the present communication, we present the analyses of a meteoritic sample, the pallasite Seymchan, which is rich in the mineral schreibersite and was allowed to corrode for eight years in water. At room temperature, the schreibersite corroded in water to give P species including phosphate and phosphite. These results indicate that phosphite is not an ephemeral species and it is stable enough to be detected in multiple environments.In-fall of extraterrestrial material including meteorites and interstellar dust particles during the late heavy bombardment are known to have brought substantial amounts of reduced oxidation-state phosphorus to the early Earth in the form of siderophilic minerals, e.g., schreibersite ((FeNi)3P). In this report, we present results on the reaction of meteoritic phosphide minerals in the Seymchan meteorite in ultrapure water for 8 years. The ions produced during schreibersite corrosion (phosphite, hypophosphate, pyrophosphate, and phosphate) are stable and persistent in aqueous solution over this timescale. These results were also compared with the short-term corrosion reactions of the meteoritic mineral schreibersite’s synthetic analog Fe3P in aqueous and non-aqueous solutions (ultrapure water and formamide). This finding suggests that the reduced-oxidation-state phosphorus (P) compounds including phosphite could be ubiquitous and stable on the early Earth over a long span of time and such compounds could be readily available on the early Earth.

Raman Spectroscopy Studies of Equilibrated Ordinary Chondrites with H and L Group and Shock Metamorphism Degrees

Ordinary chondrites are the most common type of chondrites. As a non-destructive, rapid, and semi-quantitative technology, Raman spectroscopy is widely used in geoscience. This paper presents the results of a Raman spectroscopic study that we conducted for 16 ordinary chondrites with different chemical groups and variable degrees of shock metamorphism. We found that: (1) the relationship between the Fe composition of olivine and pyroxene and the characteristic peaks of the Raman spectrum established by predecessors cannot be refined to the range of meteorites, the shock on meteorites also affects the Raman spectral characteristics of minerals and (2) the full width at half maximum (FWHM) of the shocked minerals (including high-pressure minerals) in meteorites increases in the Raman spectrum, however, no clear numerical relationship with pressure was found. Based on these data, we assess that the feasibility of Raman spectroscopy for the classification of chemical group and shock metamorphism in ordinary chondrites is not well established.

Kinetic isotope effects in H2O2 self-decomposition: Implications for triple oxygen isotope systematics of secondary minerals in the solar system

Hydrogen peroxide (H2O2) is a ubiquitous molecule in nature that shapes the redox state of planetary surfaces. Given that H2O2 is a major oxidant, isotope effects associated with H2O2 chemistry play a key role in determining triple oxygen isotopic compositions (δ17O and δ18O) of secondary aerosols and minerals, which are powerful proxies for understanding terrestrial/Martian atmospheric chemistry, and chemical evolution in the solar nebular. However, isotope effects in H2O2 self-decomposition processes, which actively occur in nature due to the thermal instability of H2O2, remains poorly understood. Here, we report a hitherto overlooked large and mass-dependent isotope fractionation in aqueous H2O2 self-decomposition processes quantified in a series of kinetic experiments. δ18O in remaining H2O2 is several tens of per mil (‰) with respective to initial H2O2. By synthesizing triple oxygen isotope measurements of natural H2O2, ozone, various oxyanions formed in the atmosphere (sulfate, nitrate, perchlorate, and carbonate), and oxygen-bearing secondary minerals in meteorites, we find that a decoupled Δ17O–δ18O pattern in natural H2O2 is attributed in part to the high degree of mass-dependent δ18O variation in H2O2 decomposition, and further argue that this unique signature may play a crucial role in triple oxygen isotope systematics in a board spectrum of secondary minerals in our solar system including aerosols, sediments, and meteorites. Our results shed fresh insights into recent debates on the role of H2O2 in the formation of these secondary minerals in the modern Earth, geological past, and other planets. The isotope effect experimentally quantified in this study are needed for future improvements of planetary atmosphere and solar nebular evolution models. We highlight the importance of further experimental and theoretical efforts to quantify isotope effects in H2O2 chemistry that are representative of natural systems.

Shock Recovery With Decaying Compressive Pulses: Shock Effects in Calcite (CaCO3) Around the Hugoniot Elastic Limit

AbstractShock metamorphism of minerals in meteorites provides insights into the ancient Solar System. Calcite is an abundant aqueous alteration mineral in carbonaceous chondrites. Return samples from the asteroids Ryugu and Bennu are expected to contain calcite‐group minerals. Although shock metamorphism in silicates has been well studied, such data for aqueous alteration minerals are limited. Here, we investigated the shock effects in calcite with marble using impact experiments at the Planetary Exploration Research Center of Chiba Institute of Technology. We produced decaying compressive pulses with a smaller projectile than the target. A metal container facilitates recovery of a sample that retains its pre‐impact stratigraphy. We estimated the peak pressure distributions in the samples with the iSALE shock physics code. The capability of this method to produce shocked grains that have experienced different degrees of metamorphism from a single experiment is an advantage over conventional uniaxial shock recovery experiments. The shocked samples were investigated by polarizing microscopy and X‐ray diffraction analysis. We found that more than half of calcite grains exhibit undulatory extinction when peak pressure exceeds 3 GPa. This shock pressure is one order of magnitude higher than the Hugoniot elastic limit (HEL) of marble, but it is close to the HEL of a calcite crystal, suggesting that the undulatory extinction records dislocation‐induced plastic deformation in the crystal. Finally, we propose a strategy to re‐construct the maximum depth of calcite grains in a meteorite parent body, if shocked calcite grains are identified in chondrites and/or return samples from Ryugu and Bennu.

Formation and decomposition of vacancy-rich clinopyroxene in a shocked eucrite: New insights for multiple impact events

Impact is a fundamental process shaping the formation and evolution of planets and asteroids. It is inevitable that some materials on the surface of planets and asteroids have been impacted for many times. However, unambiguous petrological records for multiple post-formation impact events are rarely described. Here, we report that the thin shock melt veins of the shocked eucrite Northwest Africa 8647 are dominated by a fine-grained intergranular or vermicular pigeonite and anorthite assemblage, rather than compact vacancy-rich clinopyroxene. Vacancy-rich clinopyroxene in the veins instead is ubiquitous as irregularly-shaped, relict grains surrounded by intergranular or vermicular pigeonite and anorthite assemblage. The silica fragments entrained in shock melt veins contain a coesite core and a quartz rim. The occurrences of vacancy-rich clinopyroxene and coesite can be best explained by two impact events. The first impact event produced the shock melt veins and lead to the formation of vacancy-rich clinopyroxene and coesite. The second impact event heated the fine-grained melt veins and lead to the widespread partial decomposition of vacancy-rich clinopyroxene and the partial back-transformation of coesite. This paper is the first report of the decomposition reaction of shock-induced vacancy-rich clinopyroxene in extraterrestrial materials. We propose that widespread decomposition and/or back-transformation of high-pressure minerals in shocked meteorites can be considered as important records of multiple impact events.

A Survey of Meteorite-specific Minerals

Abstract Dozens of exotic materials are found only in meteorites. These “meteorite minerals” are formed in the solar system's cold, long-lived, proto-planetary disk, in the slowly cooling cores of planetesimals, and in high-speed collisions. To the best of our knowledge no recent published work has aggregated information about minerals only found in meteorites in a comprehensive and machine readable manner. Thus, we have compiled a preliminary catalog of 81 known meteorite minerals from the literature to serve as a stepping stone for a future, more extensive effort. We also explore the distribution of these meteorite minerals by meteorite type.

Formation, preservation and extinction of high-pressure minerals in meteorites: temperature effects in shock metamorphism and shock classification

The goal of classifying shock metamorphic features in meteorites is to estimate the corresponding shock pressure conditions. However, the temperature variability of shock metamorphism is equally important and can result in a diverse and heterogeneous set of shock features in samples with a common overall shock pressure. In particular, high-pressure (HP) minerals, which were previously used as a solid indicator of high shock pressure in meteorites, require complex pressure–temperature–time (P–T–t) histories to form and survive. First, parts of the sample must be heated to melting temperatures, at high pressure, to enable rapid formation of HP minerals before pressure release. Second, the HP minerals must be rapidly cooled to below a critical temperature, before the pressure returns to ambient conditions, to avoid retrograde transformation to their low-pressure polymorphs. These two constraints require the sample to contain large temperature heterogeneities, e.g. melt veins in a cooler groundmass, during shock. In this study, we calculated shock temperatures and possible P–T paths of chondritic and differentiated mafic–ultramafic rocks for various shock pressures. These P–T conditions and paths, combined with observations from shocked meteorites, are used to constrain shock conditions and P–T–t histories of HP-mineral bearing samples. The need for rapid thermal quench of HP phases requires a relatively low bulk-shock temperature and therefore moderate shock pressures below ~ 30 GPa, which matches the stabilities of these HP minerals. The low-temperature moderate-pressure host rock generally shows moderate shock-deformation features consistent with S4 and, less commonly, S5 shock stages. Shock pressures in excess of 50 GPa in meteorites result in melt breccias with high overall post-shock temperatures that anneal out HP-mineral signatures. The presence of ringwoodite, which is commonly considered an indicator of the S6 shock stage, is inconsistent with pressures in excess of 30 GPa and does not represent shock conditions different from S4 shock conditions. Indeed, ringwoodite and coexisting HP minerals should be considered as robust evidence for moderate shock pressures (S4) rather than extreme shock (S6) near whole-rock melting.

Nazarovite, Ni12P5, a new terrestrial and meteoritic mineral structurally related to nickelphosphide, Ni3P

Abstract Nazarovite, Ni12P5, is a new natural phosphide discovered on Earth and in meteorites. Terrestrial nazarovite originates from phosphide assemblages confined to pyrometamorphic suite of the Hatrurim Formation (the Mottled Zone), the Dead Sea basin, Negev desert, Israel. Meteoritic nazarovite was identified among Ni-rich phosphide precipitates extracted from the Marjalahti meteorite (main group pallasite). Terrestrial mineral occurs as micrometer-sized lamella intergrown with transjordanite (Ni2P). Meteoritic nazarovite forms chisel-like crystals up to 8 μm long. The mineral is tetragonal, space group I4/m. The unit-cell parameters of terrestrial and meteoritic material, respectively: a 8.640(1) and 8.6543(3), c 5.071(3), and 5.0665(2) Å, V 378.5(2), and 379.47(3) Å3, Z = 2. The crystal structure of terrestrial nazarovite was solved and refined on the basis of X-ray single-crystal data (R1 = 0.0516), whereas the structure of meteoritic mineral was refined by the Rietveld method using an X-ray powder diffraction profile (RB = 0.22%). The mineral is structurally similar to phosphides of schreibersite–nickelphosphide join, Fe3P-Ni3P. Chemical composition of nazarovite (terrestrial/meteoritic, electron microprobe, wt%): Ni 81.87/78.59, Fe <0.2/4.10; Co <0.2/0.07, P 18.16/17.91, total 100.03/100.67, leading to the empirical formula Ni11.97P5.03 and (Ni11.43Fe0.63Co0.01)12.07P4.94, based on 17 atoms per formula unit. Nazarovite formation in nature, both on Earth and in meteorites, is related to the processes of Fe/Ni fractionation in solid state, at temperatures below 1100 °C.