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Life on Earth shows preference toward the set of organics with particular spatial configurations. Enantiomeric excesses have been observed for α-methyl amino acids in meteorites, which suggests that chiral asymmetry might have an abiotic origin. A possible abiotic mechanism that could produce chiral asymmetry in meteoritic amino acids is their formation under the influence of asymmetric catalysts, as mineral crystallization can produce spatially asymmetric structures. Although magnetite plaquettes have been proposed to be a possible candidate for an asymmetric catalyst, based on the suggestion that they have a spiral structure, a comprehensive description of their morphology and interpretation of the mechanism associated with symmetry-breaking in biomolecules remain elusive. Here we report observations of magnetite plaquettes in carbonaceous chondrites (CC) that were made with scanning electron microscopy and synchrotron X-ray computed microtomography (SXRCT). We obtained the crystal orientation of the plaquettes using electron backscatter diffraction (EBSD) analysis. SXRCT permits visualization of the internal features of the plaquettes. It provides an unambiguous conclusion that the plaquettes are devoid of a spiral feature and, rather that they are stacks of individual magnetite disks that do not join to form a continuous spiral. Despite the lack of spiral features, our EBSD data show significant changes in crystal orientation between adjacent magnetite disks. The magnetite disks are displaced in a consistent relative direction that lead to an overall crystallographic rotational mechanism. This work offers an explicit understanding of the structures of magnetite plaquettes in CC, which provides a fundamental basis for future interpretation of the proposed symmetry-breaking mechanism.

Brownleeite, ideally stoichiometric MnSi, is a manganese silicide not previously observed in nature that was discovered within an interplanetary dust particle that likely originated from a comet. Three submicrometer brownleeite grains were found, with one of them poikilitically enclosed by Mnbearing forsterite. Owing to the small size of the brownleeite grains, it was not possible to determine conventional macroscopic properties of this mineral; however, the chemical composition and crystal structure were well constrained by extensive quantitative energy dispersive X-ray analysis and electron diffraction using transmission electron microscopy (TEM). The crystal system for brownleeite is cubic (a = 4.557 Å) with space group P213, cell volume = 94.63 Å3, Z = 4, density (calculated) = 2.913 g/cm3, and empirical formula: (Mn0.77Fe0.18Cr0.05)Si. These brownleeite grains likely formed as high-temperature condensates either in the early Solar System or in the outflow of an evolved star or supernova explosion.

Abstract—Organic contamination (˜2965 and ˜1260 cm−1peaks) was found on Tagish Lake (C2) and Murchison (CM2) carbonaceous chondrites containing abundant hydrous minerals by Fourier transform infrared (FTIR) microspectroscopy on the samples pressed on Al plates. On the other hand, anhydrous chondrite (Moss, CO3) was not contaminated. This contamination occurred within one day of storage, when the samples pressed on Al were stored within containers including silicone rubber mats. Volatile molecules having similar peaks to the contaminants were detected by long‐path gas cell FTIR measurements for the silicone rubber mat. Rapid adsorption of the volatile contaminants also occurred when silica gel and hydrous minerals such as serpentine were stored in containers including silicone rubber, silicone grease, or adhesive tape. However, they did not show any contamination when stored in glass and polystyrene containers without these compounds. Therefore, precious astronomical samples such as meteorites, interplanetary dust particles (IDPs), and mission‐returned samples from comets, asteroids, and Mars, should be measured by micro FTIR within one day of storage in glass containers without silicone rubber, silicone grease, or adhesive tape.

Japan Aerospace Exploration Agency (JAXA) will launch a spacecraft in 2024 for a sample return mission from Phobos (Martian Moons eXploration: MMX). Touchdown operations are planned to be performed twice at different landing sites on the Phobos surface to collect > 10 g of the Phobos surface materials with coring and pneumatic sampling systems on board. The Sample Analysis Working Team (SAWT) of MMX is now designing analytical protocols of the returned Phobos samples to shed light on the origin of the Martian moons as well as the evolution of the Mars–moon system. Observations of petrology and mineralogy, and measurements of bulk chemical compositions and stable isotopic ratios of, e.g., O, Cr, Ti, and Zn can provide crucial information about the origin of Phobos. If Phobos is a captured asteroid composed of primitive chondritic materials, as inferred from its reflectance spectra, geochemical data including the nature of organic matter as well as bulk H and N isotopic compositions characterize the volatile materials in the samples and constrain the type of the captured asteroid. Cosmogenic and solar wind components, most pronounced in noble gas isotopic compositions, can reveal surface processes on Phobos. Long- and short-lived radionuclide chronometry such as 53Mn–53Cr and 87Rb–87Sr systematics can date pivotal events like impacts, thermal metamorphism, and aqueous alteration on Phobos. It should be noted that the Phobos regolith is expected to contain a small amount of materials delivered from Mars, which may be physically and chemically different from any Martian meteorites in our collection and thus are particularly precious. The analysis plan will be designed to detect such Martian materials, if any, from the returned samples dominated by the endogenous Phobos materials in curation procedures at JAXA before they are processed for further analyses.

The Stardust spacecraft successfully returned dust from comet 81P/Wild 2 to Earth in January 2006. Preliminary examination of the samples showed abundant crystalline silicates comparable to those found in chondritic meteorites presumably formed in the asteroid belt. Here, we report results of a transmission electron microscopy (TEM) study of a pyroxene-bearing terminal particle, which contains lamellar intergrowths of pigeonite and diopside on the (001) plane. This microstructure is typical for an igneous process and formation by exsolution during cooling. Width and wavelength of the lamellae indicate a cooling rate within the range 10-100 °C/h, in close agreement with those of chondrules or lava from an asteroidal igneous rock. This observation shows that some Stardust material experienced periods of igneous processing similar to material found in the inner early solar system. This implies that igneous materials were common materials in a large region of the protoplanetary disk and were not restricted to the asteroid belt. Their presence in comet Wild 2 also supports the favored view of large radial mixing from the inner to the outer regions before the comet’s accretion.

Abstract—We report the discovery that impacts in the Stardust cometary collector are not distributed randomly in the collecting media, but appear to be clustered on scales smaller than ˜10 cm. We also report the discovery of at least two populations of oblique tracks. We evaluate several hypotheses that could explain the observations. No hypothesis is consistent with all the observations, but the preponderance of evidence points toward at least one impact on the central Whipple shield of the spacecraft as the origin of both clustering and low‐angle oblique tracks. High‐angle oblique tracks unambiguously originate from a non‐cometary impact on the spacecraft bus just forward of the collector.

Abstract—Sections of seven cometary fragments extracted from the aerogel collector flown on the Stardust mission to comet 81P/Wild 2 were investigated with TOF‐SIMS. These grains showed a rather heterogeneous chemical and mineralogical composition on a submicrometer scale. However, their average chemical composition is close to bulk CI chondritic values, which is consistent with analyses of numerous Stardust samples using various techniques. As a result, the TOF‐SIMS analyses support the conclusion that Wild 2 has a CI‐like bulk composition. The cometary particles resemble anhydrous chondritic porous interplanetary dust particles, which have previously been suggested to originate from comets. For one of the fragments, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed.

Abstract—Cometary matter in aerogel samples from the Stardust mission was investigated with TOF‐SIMS for its elemental and organic composition. While single grains >1 μm are highly variable in their chemical composition, nanometer‐scale material found in the wall of one track has within a factor of 1.22 bulk CI chondritic element ratios relative to Fe for Na, Mg, A1, Ti, Cr, Mn, and Co. Compared to CI, a depletion in Ca by a factor of four and an enrichment in Ni by a factor of two was observed. These results seem to confirm recent reports of a CI‐like bulk composition of Wild 2. The analysis of organic compounds in aerogel samples is complicated by the presence of contaminants in the capture medium. However, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed.

Abstract—Aqueous and thermal processing of primordial materials occurred prior to and during planet formation in the early solar system. A record of how solid materials were altered at this time is present in the carbonaceous chondrites, which are naturally delivered fragments of primitive asteroids. It has been proposed that some materials, such as the clasts termed “dark inclusions” found in type III chondrites, suggest a sequence of aqueous and thermal events. Lithium isotopes (6Li and 7Li) can reveal the role of liquid water in dark inclusion history. During aqueous alteration, 7Li passes preferentially into solution leaving 6Li behind in the solid phase and, consequently, any relatively extended periods of interaction with 7Li‐rich fluids would have left the dark inclusions enriched in the heavier isotope when compared to the meteorite as a whole. Our analyses of lithium isotopes in Allende and its dark inclusions reveal marked isotopic homogeneity and no evidence of greater levels of aqueous alteration in dark inclusion history.

Abstract—We have studied the CB carbonaceous chondrites Queen Alexandra Range (QUE) 94411, Hammadah al Hamra (HH) 237, and Bencubbin with an emphasis on the petrographical and mineralogical effects of the shock processing that these meteorite assemblages have undergone. Iron‐nickel metal and chondrule silicates are the main components in these meteorites. These high‐temperature components are held together by shock melts consisting of droplets of dendritically intergrown Fe,Ni‐metal/sulfide embedded in silicate glass, which is substantially more FeO‐rich (30–40 wt%) than the chondrule silicates (FeO <5 wt%). Fine‐grained matrix material, which is a major component in most other chondrite classes, is extremely scarce in QUE 94411 and HH 237, and has not been observed in Bencubbin. This material occurs as rare, hydrated matrix lumps with major and minor element abundances roughly similar to the ferrous silicate shock melts (and CI). We infer that hydrated, fine‐grained material, compositionally similar to these matrix lumps, was originally present between the Fe,Ni‐metal grains and chondrules, but was preferentially shock melted. Other shock‐related features in QUE 94411, HH 237, and Bencubbin include an alignment and occasionally strong plastic deformation of metal and chondrule fragments.

Abstract The hydroxyl in phyllosilicate minerals is the most common occurrence of water in primitive meteorites. Direct hydrogen isotopic analysis of this water component using an ion microprobe has been made in some glassy or phyllosilicate spherules from the Al Rais (CR) and Orgueil (CI) chondrites. The spherules from Al Rais show large deuterium excesses (δD= +200 – +800‰) relative to terrestrial standards, whereas deuterium‐enrichments in the spherules from Orgueil are much smaller (δD = +40 – +130‰). The phyllosilicate spherules are products of aqueous alteration of glassy precursors. In Al Rais the phyllosilicate spherules have relatively higher δDvalues than the glassy ones, indicating that water introduced during aqueous alteration was deuterium‐enriched. The deuterium‐enrichments in the phyllosilicate spherules from Orgueil could result from isotopic exchange under thermodynamic conditions within the solar nebula. The much larger δDexcesses of the Al Rais spherules, however, cannot be attributed to the similar process; instead, an interstellar origin needs to be invoked.

Abstract—The Meteoritical Bulletin No. 88 lists information for 1610 newly classified meteorites, comprising 753 from Antarctica, 302 from Africa, 505 from Asia (495 of which are from Oman), 40 from North America, 5 from South America, 4 from Europe, and 1 of unknown origin. Information is provided for 9 falls (Alby sur Chéran, Al Zarnkh, Devgaon, Kamioka, Kendrapara, Maromandia, New Orleans, Sivas, and Villalbeto de la Peña). Noteworthy specimens include a eucrite fall (Alby sur Chéran), 6 martian meteorites, 13 lunar meteorites, and 12 irons including one weighing 3 metric tons (Dronino).

Recent models for the origin of Jupiter indicate that the Galilean satellites were mostly derived from largely unprocessed solar nebula solids and planetesimals. In the jovian subnebula the solids that built Europa were first heated and then cooled, but the major effect was most likely partial or total devolatilization, and less likely to have been wholesale thermochemical reprocessing of rock + metal compositions (e.g., oxidation of Fe and hydration of silicates). Ocean formation and substantial alteration of interior rock by accreted water and ice would occur during and after accretion, but none of the formation models predicts or implies accretion of sulfates. Europa's primordial ocean was most likely sulfidic. After accretion and later radiogenic and tidal heating, the primordial ocean would have interacted hydrothermally with subjacent rock. It has been hypothesized that sulfides could be converted to sulfates if sufficient hydrogen was lost to space, but pressure effects and the impermeability of serpentinite imply that extraction of sulfate from thoroughly altered Europa-rock would have been inefficient (if indeed Mg sulfates formed at all). Permissive physical limits on the extent of alteration limit the sulfate concentration of Europa's evolved ocean to 10% by weight MgSO4 or equivalent. Later oxidation of the deep interior of Europa may have also occurred because of water released by the breakdown of hydrated silicates, ultimately yielding S magma and/or SO2 gas. Geological and astrobiological implications are considered.

Abstract—Clasts of alkaline (the second find in meteorites) and subalkaline rocks were found in the Kaidun meteorite. One of them (#d4A) is a large crystal of albite with inclusions of fluorapatite, arfvedsonite, aenigmatite, and wilkinsonite. The two latter minerals were previously unknown in meteorites. Another clast (#d[3–5]D) has a melt crystallization texture of mainly feldspar (oligoclase) composition and contains relict grains of both high‐Ca and low‐Ca pyroxene and fluorapatite. The mineralogical characteristics of these clasts suggest a genetic relationship and an origin from the same parent body. The textural and mineralogical characteristics of the clasts indicate origin by extensive igneous differentiation. Such processes most likely took place in a rather large differentiated body. The material of clast #d(3–5)D is similar in some mineralogical respects to basaltic shergottites.

Abstract—We describe the petrologic and trace element characteristics of the Yamato 86029 (Y‐86029) meteorite. Y‐86029 is a breccia consisting of a variety of clasts, and abundant secondary minerals including coarse‐ and fine‐grained phyllosilicates, Fe‐Ni sulfides, carbonates, and magnetite. There are no chondrules, but a few anhydrous olivine‐rich grains are present within a very fine‐grained phyllosilicate‐rich matrix.

We report the first in situ observation of hollow organic globules in any extraterrestrial material using the Tagish Lake carbonaceous chondrite. Data from analytical transmission electron microscopy, Raman and micro-Fourier-transform infrared (FTIR) spectroscopy indicate that the globules consist of aliphatic and oxygenated functions. The hollow spherical morphologies are strikingly similar to the material produced by the laboratory simulation of ultraviolet photolysis of interstellar ice analogues and subsequent aqueous processing, suggesting that the organic globules in the Tagish Lake meteorite may be extremely primitive organic material that formed before or during the formation of the solar system. The FTIR organic signatures also show strong similarities to the membrane-like products formed from hydrothermal reaction of an OH-bearing amino acid in the presence of hydrous minerals. The survival of the structures in the Tagish Lake sample indicates that primitive meteorites must have delivered these structures to the early Earth as a possible precursor to life.

Abstract—It has now been about a decade since the first demonstrations that hypervelocity particles could be captured, partially intact, in aerogel collectors. But the initial promise of a bonanza of partially‐intact extraterrestrial particles, collected in space, has yet to materialize. One of the difficulties that investigators have encountered is that the location, extraction, handling and analysis of very small (10 μm and less) grains, which constitute the vast majority of the captured particles, is challenging and burdensome. Furthermore, current extraction techniques tend to be destructive over large areas of the collectors. Here we describe our efforts to alleviate some of these difficulties. We have learned how to rapidly and efficiently locate captured particles in aerogel collectors, using an automated microscopic scanning system originally developed for experimental nuclear astrophysics. We have learned how to precisely excavate small access tunnels and trenches using an automated micromanipulator and glass microneedles as tools. These excavations are only destructive to the collector in a very small area—this feature may be particularly important for excavations in the precious Stardust collectors. Using actuatable silicon microtweezers, we have learned how to extract and store “naked” particles—essentially free of aerogel—as small as 3 μm in size. We have also developed a technique for extracting particles, along with their terminal tracks, still embedded in small cubical aerogel blocks. We have developed a novel method for storing very small particles in etched nuclear tracks. We have applied these techniques to the extraction and storage of grains captured in aerogel collectors (Particle Impact Experiment, Orbital Debris Collector Experiment, Comet‐99) in low Earth orbit.

Abstract—Fine‐grained, heavily‐hydrated lithic clasts in the metal‐rich (CB) chondrites Queen Alexandra Range (QUE) 94411 and Hammadah al Hamra 237 and CH chondrites, such as Patuxent Range (PAT) 91546 and Allan Hills (ALH) 85085, are mineralogically similar suggesting genetic relationship between these meteorites. These clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite, prismatic sulfides (pentlandite and pyrrhotite), and Fe‐Mn‐Mg‐bearing Ca‐carbonates set in a phyllosilicate‐rich matrix. Two types of phyllosilicates were identified: serpentine, with basal spacing of ˜0.73 nm, and saponite, with basal spacings of about 1.1–1.2 nm. Chondrules and FeNi‐metal grains in CB and CH chondrites are believed to have formed at high temperature (>1300 K) by condensation in a solar nebula region that experienced complete vaporization. The absence of aqueous alteration of chondrules and metal grains in CB and CH chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the CH and CB parent bodies. The hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and FeNi‐metal grains after these high‐temperature components had been transported from their hot formation region to a much colder region of the solar nebula.

Abstract—Zag and Monahans (1998) are H‐chondrite regolith breccias comprised mainly of light‐colored metamorphosed clasts, dark clasts that exhibit extensive silicate darkening, and a halite‐bearing clastic matrix. These meteorites reflect a complex set of modification processes that occurred on the H‐chondrite parent body. The light‐colored clasts are thermally metamorphosed H5 and H6 rocks that were fragmented and deposited in the regolith. The dark clasts formed from light‐colored clasts during shock events that melted and mobilized a significant fraction of their metallic Fe‐Ni and troilite grains. The clastic matrices of these meteorites are rich in solar‐wind gases. Parent‐body water was required to cause leaching of chondritic minerals and chondrule glass; the fluids became enriched in Na, K, Cl, Br, Al, Ca, Mg and Fe. Evaporation of the fluids caused them to become brines as halides and alkalies became supersaturated; grains of halite (and, in the case of Monahans (1998), halite with sylvite inclusions) precipitated at low temperatures (≤100 °C) in the porous regolith. In both meteorites fluid inclusions were trapped inside the halite crystals. Primary fluid inclusions were trapped in the growing crystals; secondary inclusions formed subsequently from fluid trapped within healed fractures.

Abstract—White sulfate veins are a very well‐known petrological feature of the chemically primitive CI1 carbonaceous chondrites. Sulfate veins were first described in the Orgueil meteorite in 1961, almost one century after its fall. However, we have observed such veins to form easily during typical sample storage. We suggest that all CI1 sulfate veins formed during the terrestrial residence of these heavily brecciated, porous stones. Reacting with atmospheric water, sulfates originally present in the meteorites dissolved and remobilized, and/or sulfides oxidised, filling the many open spaces offered to them by the very porous rock. Sulfate veins in CI1 chondrites can no longer be used as evidence of a late‐stage oxidation event in the CI1 parent body, or of centimeter‐scale fluid transport on the parent asteroid.

Abstract—The carbonaceous chondrite MacAlpine Hills (MAC) 88107 has bulk composition and mineralogy that are intermediate between those of CO and CM chondrites. This meteorite experienced minor alteration and a low degree of thermal metamorphism (petrologic type 3.1) and escaped post‐accretional brecciation. The alteration resulted in the formation of fayalite (Fa90–100). Al‐free hedenbergite (∼Fs50Wo50), phyllosilicates (saponite‐serpentine intergrowths), magnetite, and Ni‐bearing sulfides (pyrrhotite and pentlandite). Fayalite and hedenbergite typically occur as veins, which start at the opaque nodules in the chondrule peripheries, crosscut fine‐grained rims and either terminate at the boundaries with the neighboring fine‐grained rims or continue as layers between these rims. These observations suggest that fayalite and hedenbergite crystallized after accretion and compaction of the fine‐grained rims. Fayalite also overgrows isolated forsteritic (Fa1–5) and fayalitic (Fa20–40) olivine grains without any evidence for Fe‐Mg interdiffusion; it also replaces massive magnetite‐sulfide grains. The initial 53Mn/55Mn ratio of (1.58 ± 0.26) × 10−6in the MAC 88107 fayalite corresponds to an age difference between the formation of fayalite and refractory inclusions in Allende of either ∼9 or 18 Ma, depending upon the value of the solar system initial abundance of 53Mn used in age calculations.

Abstract—Fine‐grained, optically opaque rims coat individual olivine and pyroxene grains in CM matrices and chondrules. Bulk chemical analyses and observations of these rims indicate the presence of phyllosilicates and disseminated opaques. Because phyllosilicates could not have survived the chondrule formation process, chondrule silicate rims must have formed entirely by late‐state aqueous reactions. As such, these textures provide a useful benchmark for isolating alteration features from more complex CM matrix materials. Both chondrule silicate and matrix silicate rims exhibit morphological features commonly associated with advancing stages of replacement reactions in terrestrial serpentinites. Contacts between many matrix silicate rims and the adjacent matrix materials suggest that these rims formed entirely by aqueous reactions in a parent‐body setting. This contrasts with previous assertions that rim textures can only form by the accretion of nebular dust but does not imply an origin for the rims surrounding other types of CM core components, such as chondrules.

Florenskyite is a new phosphide species from the Kaidun chondritic meteorite, which fell in South Yemen in 1980. Kaidun is a unique chondritic breccia containing a huge variety of fragments of different chondritic types. Florenskyite was found as four dispersed grains with a maximum dimension of 14 μm within a single mass of Fe-rich serpentine within one Kaidun clast. Florenskyite is associated with submicrometer-sized grains of pentlandite and small (up to 1.5 μm in width) laths of a still uncharacterized Fe-Cr phosphide. Florenskyite is creamy white in reflected light, and its luster is metallic. The average of three electron microprobe analyses gave (wt%) Fe 40.52, Ti 30.08, Ni 5.47, Cr 0.93, V 0.91, Co 0.60, P 21.69, Si 0.59, sum 100.79, corresponding to Fe1.01(Ti0.87Ni0.13Cr0.03V0.02Co0.01)1.06(P0.97Si0.03). Single-crystal structure analysis was performed on florenskyite using a Laue pattern collected from a multiple crystal by in-situ synchrotron X-ray diffraction. Florenskyite crystallizes in the space group Pnma, and has the anti-PbCl2structure. Previously determined cell constants of synthetic material [a = 6.007(1), b = 3.602(1), c = 6.897(1) Å] were used in the single-crystal data reduction. We used the POWD12 program to calculate a powder XRD pattern; the 5 most intense reflections are d = 2.301 (I = 100), 2.188 (88), 2.307 (47), 1.938 (45), and 1.801 Å (45). Florenskyite is only the fourth phosphide to be described from nature. Its paragenesis may be unique, and may be due to melting of a mineral assemblage including Fe-Ni metal, schreibersite, daubreelite, osbornite, or heideite and subsequent crystallization of phosphides from the melt.

Florenskyite is a new phosphide species from the Kaidun chondritic meteorite, which fell in South Yemen in 1980. Kaidun is a unique chondritic breccia containing a huge variety of fragments of different chondritic types. Florenskyite was found as four dispersed grains with a maximum dimension of 14 μm within a single mass of Fe-rich serpentine within one Kaidun clast. Florenskyite is associated with submicrometer-sized grains of pentlandite and small (up to 1.5 μm in width) laths of a still uncharacterized Fe-Cr phosphide. Florenskyite is creamy white in reflected light, and its luster is metallic. The average of three electron microprobe analyses gave (wt%) Fe 40.52, Ti 30.08, Ni 5.47, Cr 0.93, V 0.91, Co 0.60, P 21.69, Si 0.59, sum 100.79, corresponding to Fe1.01(Ti0.87Ni0.13Cr0.03V0.02Co0.01)1.06(P0.97Si0.03). Single-crystal structure analysis was performed on florenskyite using a Laue pattern collected from a multiple crystal by in-situ synchrotron X-ray diffraction. Florenskyite crystallizes in the space group Pnma, and has the anti-PbCl2structure. Previously determined cell constants of synthetic material [a = 6.007(1), b = 3.602(1), c = 6.897(1) Å] were used in the single-crystal data reduction. We used the POWD12 program to calculate a powder XRD pattern; the 5 most intense reflections are d = 2.301 (I = 100), 2.188 (88), 2.307 (47), 1.938 (45), and 1.801 Å (45). Florenskyite is only the fourth phosphide to be described from nature. Its paragenesis may be unique, and may be due to melting of a mineral assemblage including Fe-Ni metal, schreibersite, daubreelite, osbornite, or heideite and subsequent crystallization of phosphides from the melt.

Abstract—The oxidized CV3 chondrites can be divided into two major subgroups or lithologies, Bali‐like (CV3oxB) and Allende‐like (CV3oxA), in which chondrules, calcium‐aluminum‐rich inclusions (CAIs) and matrices show characteristic alteration features (Weisberg et al, 1997; Krot et al, 1997d; Kimura and Ikeda, 1997). The CV3oxBlithology is present in Bali, Kaba, parts of the Mokoia breccia and, possibly, in Grosnaja and Allan Hills (ALH) 85006. It is characterized by the presence of the secondary low‐Ca phyllosilicates (saponite and sodium phlogopite), magnetite, Ni‐rich sulfides, fayalite (Fa>90), Ca‐Fe‐rich pyroxenes (Fs10–50Wo45–50) and andradite. Phyllosilicates replace primary Ca‐rich minerals in chondrules and CAIs, which suggests mobilization of Ca during aqueous alteration. Magnetite nodules are replaced to various degrees by fayalite, Ca‐Fe‐rich pyroxenes and minor andradite. Fayalite veins crosscut fine‐grained rims around chondrules and extend into the matrix. Thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures (<300 °C) in the presence of aqueous solutions. Oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large Δ18Ofayalite‐magnetitefractionation (∼20%). We infer that phyllosilicates, magnetite, fayalite, Ca‐Fe‐rich pyroxenes and andradite formed at relatively low temperatures (<300 °C) by fluid‐rock interaction in an asteroidal environment.

Abstract—We have investigated the porosity of a large number of chondritic interplanetary dust particles (IDPs) and meteorites by three techniques: standard liquid/gas flow techniques, a new, noninvasive ultrasonic technique, and image processing of backscattered images. The latter technique is obviously best‐suited to sub‐kilogram sized samples. We have also measured the gas and liquid permeabilities of some chondrites by two techniques: standard liquid/gas flow techniques, and a new, nondestructive pressure release technique. We find that chondritic IDPs have a somewhat bimodal porosity distribution. Peaks are present at 0 and 4% porosity; a tail then extends to 53%. Type 1–3 chondrite matrix porosities range up to 30%, with a peak at 2%. The bulk porosities for type 1–3 chondrites have the same approximate range as exhibited by the matrix, which indicates that other components of the bulk meteorites (including chondrules and aggregates) have the same average porosity as the matrix. These results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar, which implies that similar accretion dynamics operated through 12 orders of size magnitude. Permeabilities of the investigated chondrites vary by several orders of magnitude, and there appears to be no simple dependence of permeability with degree of aqueous alteration, chondrite type or porosity.

Abstract—We measured infrared diffuse reflectance spectra of several carbonaceous chondrites in order to obtain additional information on the surface materials of their presumed parent bodies, C‐type asteroids. The presence and intensity of absorption bands near 3 μm in the reflectance spectra are due to the presence and abundance of hydrates and/or hydroxyl ions. The absorption features of the 3 μm hydration bands of carbonaceous chondrites were compared with those of asteroids 1 Ceres and 2 Pallas. They are commonly classified into separate subtypes, G‐ and B‐type. The spectral shapes of Pallas and Renazzo (CR2 chondrite) around the 3 μm absorption band are an excellent match. This result may suggest that the amount of hydrous minerals in the surface material of Pallas is smaller than that in the CM2 or CI chondrites, and the hydrous minerals on the surface of Pallas may be similar to those found in Renazzo. The spectral features around the 3 μm band of Ceres are different from those of carbonaceous chondrites studied in this paper.

Abstract—We have studied an Allende dark inclusion by optical microscopy, scanning electron microscopy, electron microprobe analysis and transmission electron microscopy. The inclusion consists of chondrules, isolated olivines and matrix, which, as in the Allende host, is mainly composed of 5–20 μm long lath‐shaped fayalitic grains with a narrow compositional range (Fa42 ± 2) and nepheline. Olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5–10 μm wide fayalitic rims (Fa39 ± 2) and 100–1000 μm wide translucent zones, which consist of 5–20 μm long lath‐shaped fayalitic grains (Fa41 ± 1) intergrown with nepheline. These fayalitic olivines, like those in the matrix of the dark inclusion, contain 10–20 nm sized inclusions of chromite, hercynite, and Fe‐Ni sulfides. The fayalitic rims around remnant olivines are texturally and compositionally identical to those in Allende host, suggesting that they have similar origins. Chondrules are surrounded by opaque rims consisting of tiny lath‐shaped fayalitic olivines (<1–3 μm long) intergrown with nepheline. As in the Allende host, fayalitic olivine veins may crosscut altered chondrules, fine‐grained chondrule rims and extend into the matrix, indicating that alteration occurred after accretion.

Abstract—I have reinvestigated the mineralogy of the only carbonaceous chondrite (12037, 188) returned from the Moon and found saponite within, which comprises the first hydrous material returned from the Moon. That this phyllosilicate has survived impact onto the lunar surface suggests that asteroid and cometary impacts could have provided significant quantities of surviving clay (hydrous) minerals into the lunar regolith. The Bench Crater meteorite also provides a glimpse of the petrography of the ancient meteoroid complex, something not possible on the geologically active Earth.

Abstract—Fayalitic olivine (Fa54–94) is a ubiquitous component in the matrix of Krymka (LL3.1) as well as in other highly unequilibrated chondrites (ordinary and carbonaceous). In Krymka, the fayalitic olivine has an unusual anisotropic platy morphology that occurs in at least five types of textural settings that can be characterized as: (1) isolated platelets, (2) clusters of platelets, (3) euhedral to subhedral crystals, (4) overgrowths of platelets on forsteritic olivine, and (5) fluffy (porous) aggregates. From transmission electron microscope (TEM) investigation, the direction of elongation of the platy olivine overgrowths on forsteritic olivine substrates is along the caxis and in most cases it corresponds with the caxis of the substrate olivine, which suggests that the fayalitic olivine grew in this unusual morphology and is not a replacement product of preexisting material. The fayalitic olivine in the matrix of Krymka is compositionally similar to olivine with platy morphology in the matrix of some CV3 chondrites and both have similar Fe/Mn ratios, but important morphological differences indicate that their relationship needs to be explored further. Textural and compositional data indicate that the fayalitic olivine in the matrix of Krymka, as well as in some other unequilibrated ordinary chondrites, formed prior to final lithification of the meteorite and probably prior to parent body accretion. We find that formation of the fayalitic olivine by vapor‐solid growth provides the best explanation for our observations and data and is the only feasible mechanism for the formation of fayalitic olivine in the matrix of Krymka. We propose that the fayalitic olivine formed by vaporization and recondensation of olivine rich‐dust, during a period of enhanced dust/gas ratio in the nebula.

Abstract—We have characterized Ca‐Fe‐rich silicates (salite‐hedenbergite pyroxenes (Fs10–50Wo45–50), andradite (Ca3Fe2Si3O12), kirschsteinite (CaFeSiO4), and wollastonite (Ca3Si3O9)) in the type I chondrules and matrices in the Bali‐like and Allende‐like oxidized CV3 chondrites and Allende dark inclusions. In type I chondrules in the Bali‐like CV3 chondrites, metal is oxidized to magnetite; magnetite‐sulfide nodules are replaced by Ca‐Fe‐rich pyroxenes with minor andradite and pure fayalite. We infer that Ca‐Fe‐rich pyroxenes, andradite, fayalite, magnetite, and phyllosilicates (which occur in mesostases) formed at relatively low temperatures (<300 °C) in the presence of aqueous solutions. Thermodynamic analysis of phase relations in the Si‐Fe‐Ca‐O‐H system and large O isotopic fractionation of the coexisting magnetite and fayalite (∼20%) (Krot et al., 1998) are consistent with this interpretation.

Abundant carbide-magnetite assemblages occur in matrix, chondrules, and chondrule rims in several H3, L3, and LL3 chondrites. Carbides, cohenite ((Fe,Ni)3C), and haxonite ((Fe,Ni)23C6) show compositional variations between different meteorites and appreciable ranges within meteorites. Carbides in H chondrites have lower Co contents (0–0.6 wt%) than those in L and LL chondrites (0.3–1.2 wt%). Metal associated with carbides and magnetite consists of high-Ni (50–70 wt%) taenite and, in L and LL chondrites, Co-rich (up to 35 wt%) kamacite; minor element contents of troilite and magnetite are very low. Textural observations indicate that carbide-magnetite assemblages formed by replacement of metal-sulfide nodules. The high Co contents of residual kamacite in association with carbides indicates that Co is not incorporated into carbides (i.e., Fe/Co is much higher in the carbides than in kamacite). Because Ni in carbides and magnetite is low, the Ni contents of residual taenite tend to be high. Ni-rich sulfides were found only in LL3 chondrites, possibly indicating their more extensive oxidation and/or aqueous alteration.

Recent investigations of meteorite matrices using analytical electron microscopy and high-resolution transmission electron microscopy (HRTEM) have provided data on the structure and chemistry of poorly characterized phases (PCP)1. We suggest here that ∼10 Å PCP, a dominant matrix variety, has a structure equivalent to iron-rich tochilinite [6Fe0.9S 5(Fe, Mg) (OH)2] which consists of coherently interstratified mackinawite and brucite sheets2. In addition, we propose that ∼17 Å PCP, previously described as an SBB-type mixed-layer structure3, is a commensurate intergrowth of serpentine and tochilinite layers. A wide range of cation substitutions is possible within both tochilinite and serpentine–tochilinite structural types. We suggest that various forms of PCP observed in carbonaceous chondrites4,5are intergrowths of tochilinite, serpentine, serpentine–tochilinite and/or valleriite-type minerals6.

Carbonaceous chondrites are known to contain up to a few wt % organic carbon. Organic materials are disseminated in the clayish matrix, and some of them have been reported to be in the form of submicron organic globules. However, little is known about the nature of these microscopic organics. The organic matter distribution of the Bells (CM2) carbonaceous chondrite has been studied using a near-field infrared (NFIR) microspectrometer. Organic matter distribution and mineral associations at the submicron scale spatial resolution were observed.