Modal mineralogy of carbonaceous chondrites by X‐ray diffraction and Mössbauer spectroscopy

Abstract— Carbonaceous chondrites are among the most analyzed geological materials on Earth. However, despite this attention, and unlike most terrestrial rocks, little is known on the abundance of individual phases within them. Here, we show how a combination of several novel X‐ray diffraction (XRD) techniques (including a high‐brightness X‐ray MicroSource®), and Mössbauer spectroscopy, allows a complete modal mineralogy to be ascertained from even the most highly unequilibrated, fine‐grained chondrites for all minerals of abundance >1 wt%. Knowledge of the modal mineralogy of a sample also allows us to calculate grain density. We analyzed Allende, Murchison, Tagish Lake, and Orgueil. Based on our modal data, the grain density estimates for Allende, Murchison, and Orgueil are close to literature values. In the case of Tagish Lake, there is no published grain density, although a bulk density measurement does exist. Taking our estimate of grain density, and the measured bulk density, we calculate an exceptionally high porosity of 41% for this meteorite, similar to some chondritic IDPs and in line with a porosity calculated from an entry model for the Tagish Lake fireball. Although it is an oxidized CV, magnetite is present in Allende at a level of <0.5 wt% or <0.3 vol%, a result that is substantiated by several other instrumental studies. This may be an oxidized meteorite, but that oxidation is not manifested in abundant magnetite. In addition, we note appreciable fayalitic olivine in Orgueil, detected by both XRD and Mössbauer. We employed MicroSource® XRD to look at heterogeneity in mineral abundance in Orgueil and found substantial variation, with phyllosilicates varying inversely with olivine. The data suggest that Orgueil was initially composed primarily of anhydrous materials, which have been partially, but not completely, altered. Although the data are preliminary, comparison between our XRD modal assessment, bulk chemistry, grain density, and Mössbauer data, suggests that our estimates of mineral abundance are robust. The advent of MicroSource® XRD allows similar modal data to be acquired from samples as small as a few hundred micrograms.     

Characterization of the matrix and fusion crust of the recent meteorite fall Ozerki L6

We studied the interior and the fusion crust of the recently recovered Ozerki L6 meteorite using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy, X‐ray diffraction (XRD), magnetization measurements, and Mössbauer spectroscopy. The phase composition of the interior and of the fusion crust was determined by means of SEM, XRD, and Mössbauer spectroscopy. The unit cell parameters for silicate crystals were evaluated from the X‐ray diffractograms and were found the same for the interior and the fusion crust. Magnetization measurements revealed a decrease of the saturation magnetic moment in the fusion crust due to a decrease of Fe‐Ni‐Co alloy content. Both XRD and Mössbauer spectroscopy show the presence of magnesioferrite in the fusion crust. The temperatures of cation equilibrium distribution between the M1 and M2 sites in silicates calculated using the data obtained from XRD and Mössbauer spectroscopy appeared to be in a good consistency: 553 and 479 K for olivine and 1213 and 1202 K for orthopyroxene.     

Primordial,thermal, and shock features of ordinary chondrites: Emulating bulk X‐ray diffraction using in‐plane rotation of polished thin sections

Using an X‐ray diffractometer, powder‐like diffraction patterns were acquired from in‐plane rotation of polished thin sections (PTSs) of 60 ordinary chondrites (23 H, 21 L, and 16 LL), in order to explore the thermal and shock metamorphism and its modifications of primordial features. The olivine (Ol) 130 peak position shown as Bragg indices clearly correlates with the chemical group for equilibrated ordinary chondrites (EOCs), while the peak is split or broad for unequilibrated ordinary chondrites (UOCs). The intensity ratio of kamacite may be useful for distinguishing the chemical group between H and L‐LL, but it is not definite because of heterogeneous terrestrial weathering of kamacite, especially in H chondrites. The summed intensities of the orthoenstatite (Oen) 511 and 421 peaks positively correlates with the metamorphic sequence from 3 to 6, while that of clinoenstatite (Cen) 22 is inversely correlated. The shock stage positively correlates with the summed full width of half maximum values of the Oen 511 and 421 peaks and the FWHM of Ol 130 peak for each class. Significant amount of Oen (Pbca) transformed through Cen (C2/c) finally to Cen (P2₁/c) is stable at high pressure for shock stage S6 (Tenham and NWA 4719). The shock melted LL chondrite is characterized by the occurrence of Cen and abundant homogeneous olivine. The effects of both thermal and shock metamorphism are thus incorporated into the bulk X‐ray diffraction (XRD) data. The bulk XRD method is useful for determining the bulk mineralogy, resulting in the classification of ordinary chondrites. The method is also applicable to samples other than PTS.     

Application of Mössbauer spectroscopy,multidimensional discriminant analysis,and Mahalanobis distance for classification of equilibrated ordinary chondrites

Mössbauer spectra of equilibrated ordinary chondrites consist of two doublets due to paramagnetic iron present in olivines and pyroxenes and two sextets due to magnetically ordered iron present in metallic phases and troilite. The spectral areas of the different mineralogical phases found by Mössbauer spectroscopy in meteorites are proportional to the number of iron atoms in this mineralogical phase. This property of Mössbauer spectra can be the basis for constructing a method for the classification of ordinary chondrites. This idea was first explored at the Mössbauer Laboratory in Kanpur. This group suggested a qualitative method based on 2‐dimensional plots of Mössbauer spectral areas and thus classified properly some meteorites. We constructed a quantitative method using Mössbauer spectral areas, multidimensional discriminant analysis, and Mahalanobis distance (4M method) to determine the probability of a meteorite to be of type H, L, or LL. Based on 59 Mössbauer spectra, we calculated by the 4M method, S _cluster , the level of similarity of the Goronyo meteorite to the clusters. On the plot of ferrosilite versus fayalite, the point representing Goronyo is located on the border between H and L areas. Calculated by the 4M method, the meteorite Goronyo is 32% similar to type H, 75% to type L, and 11% to type LL. Additional mineralogical analyses suggested that the Goronyo meteorite would be classified as type L, although it was originally reported as type H in the Meteoritical Bulletin Database.     

Analysis of ordinary chondrites using powder X‐ray diffraction: 1. Modal mineral abundances

Abstract– Powder X‐ray diffraction (XRD) is used to quantify the modal abundances (in wt%) of 18 H, 17 L, and 13 LL unbrecciated ordinary chondrite falls, which represents the complete petrologic range of equilibrated ordinary chondrites (types 4–6). The XRD technique presents an effective alternative to traditional methods for determining modal abundances, such as optical point counting and electron microprobe phase (EMP) mapping. The majority of chondrite powders in this study were previously prepared for chemical characterization from 8 to 20 g of material, which is consistent with the suggested mass (10 g) necessary to provide representative sampling of ordinary chondrites. Olivine and low‐Ca pyroxene are the most abundant phases present, comprising one‐half to three‐fourths of total abundances, while plagioclase, high‐Ca pyroxene, troilite, and metal comprise the remaining XRD‐measured mineralogy. Pigeonite may also be present in some samples, but it is fitted using a high‐Ca pyroxene standard, so exact abundances cannot be measured directly using XRD. Comparison of XRD‐measured abundances with calculated Cross, Iddings, Pirsson, Washington (CIPW) normative abundances indicates that systematic discrepancies exist between these two data sets, particularly in olivine and high‐Ca pyroxene. This discrepancy is attributed to the absence of pigeonite as a possible phase in the CIPW normative mineralogy. Oxides associated with pigeonite are improperly allocated, resulting in overestimated normative olivine abundances and underestimated normative high‐Ca pyroxene abundances. This suggests that the CIPW norm is poorly suited for determining mineralogical modal abundances of ordinary chondrites.     

Fe‐bearing phases in a ureilite fragment from the asteroid 2008 TC3 (= Almahata Sitta meteorites): A combined Mössbauer spectroscopy and X‐ray diffraction study

The iron‐bearing phases in a ureilite fragment (AS#051) from the Almahata Sitta meteorite are studied using Mössbauer spectroscopy, X‐ray diffraction (XRD), and electron microprobe analysis (EMPA). AS#051 has a typical ureilite texture of medium‐ to coarse‐grained silicates (olivine, orthopyroxene, and pigeonite) with minor opaques (Fe‐Ni metal, troilite, and graphite). The silicate compositions, determined by EMPA, are homogeneous: olivine (Fo_90.2), orthopyroxene (En_86.3Fs_8.6Wo_5.1), and pigeonite (En_81.6Fs_8.9Wo_9.5), and are similar to those of magnesian ureilites. The modal abundance of mineral phases was determined by Rietveld refinement of the powder XRD data. The Mössbauer spectra at 295 K and 78 K are composed of two sharp well‐defined paramagnetic doublets superimposed on a well‐resolved magnetic sextet and other weak absorption features. The two paramagnetic doublets are assigned to olivine and pyroxene (orthopyroxene and pigeonite), and the ferromagnetic sextet to kamacite (magnetic hyperfine field ≈ 33.2 T), in agreement with the XRD characterization. The Mössbauer results also show the presence of small amounts of troilite (FeS) and cohenite ([Fe,Ni,Co]₃C). Using the Mössbauer data, the relative abundance of each Fe‐bearing phase is determined and compared with the results obtained by XRD.     

Classification of the Didwana‐Rajod meteorite: A Mössbauer spectroscopic study

Abstract— Mössbauer spectroscopic studies of the Didwana‐Rajod chondrite, which fell on 1991 August 12 in western Rajasthan, India, are presented. The results are compared with the Mössbauer data of several enstatite and ordinary chondrites including the Dhajala chondrite for which Mössbauer data were acquired during the present study. The Didwana‐Rajod chondrite's iron phases and its oxidation states strongly suggest that it should be classified as an H‐type ordinary chondrite instead of the earlier suggestion (based on petrographic studies) that it could be an enstatite chondrite. The present study demonstrates that Mössbauer spectroscopy is a very powerful technique for aiding in the classification of meteorites.     

Weathering of ordinary chondrites from the Atacama Desert,Chile, by Mössbauer spectroscopy and synchrotron radiation X‐ray diffraction

Some terrestrial areas have climatic and geomorphologic features that favor the preservation, and therefore, accumulation of meteorites. The Atacama Desert in Chile is among the most important of such areas, known as DCA. This desert is the driest on Earth, one of the most arid, uninhabitable localities with semiarid, arid, and hyper‐arid conditions. The meteorites studied here were collected from within the DCA of San Juan and Pampa de Mejillones, located, respectively, in the Central Depression and the Coastal Range of the Atacama Desert. ⁵⁷Fe Mössbauer spectroscopy was used for quantitative analysis of the degree of weathering of the meteorites, through the determination of the proportions of the various Fe‐bearing phases and in particular the amount of oxidized iron in terrestrial alteration products. The abundance of ferric ions in weathered chondrites can be related to specific precursor compositions and to the level of terrestrial weathering. The aim of the study was the identification, quantification, and differentiation of the weathering products in the ordinary chondrites found in the San Juan and the Pampa de Mejillones areas of the Atacama Desert. The ⁵⁷Fe Mössbauer spectroscopy study was complemented by synchrotron radiation X‐ray diffraction and magnetic susceptibility measurements. The results allow a clear differentiation of the rate of weathering in meteorite samples collected from the San Juan versus the Pampa de Mejillones areas of the Atacama Desert.     

Studies and characterizations of the Al Zarnkh meteorite

Abstract— A newly fallen Sudanese meteorite named Al Zarnkh was investigated using room and liquid nitrogen temperature Mössbauer measurements, X‐ray diffraction (XRD), and electron probe microanalysis (EPMA) in conjunction with energy dispersive X‐ray microscopy. The Mössbauer spectra exhibited strong paramagnetic doublets with magnetic sextets. The doublets are assigned to olivine and pyroxene, while the magnetic sextets are assigned to troilite and kamacite. Based on microprobe analyses and textural studies, olivine is the most abundant phase and occurs as fine to medium grained laths both in the groundmass and in barred olivine chondrules. Both orthopyroxenes and clinopyroxenes are present and these tend to be granular. Plagioclase is an abundant interstitial groundmass phase. Chromites were detected in some groundmass olivine and are highly chromiumand iron‐rich with no Fe³⁺ detected. The kamacite contains small amounts of Co. The mole fraction of the Fe end‐member of olivine (fayalite) and orthopyroxene (ferrosilite) are found to be about 28% and 23%, respectively. These values are compared with that obtained from two chondritic meteorites. Based on these results, the studied meteorite is classified as an ordinary LL5 chondrite.     

Bounce Rock—A shergottite‐like basalt encountered at Meridiani Planum,Mars

Abstract– The Opportunity rover of the Mars Exploration Rover mission encountered an isolated rock fragment with textural, mineralogical, and chemical properties similar to basaltic shergottites. This finding was confirmed by all rover instruments, and a comprehensive study of these results is reported here. Spectra from the miniature thermal emission spectrometer and the Panoramic Camera reveal a pyroxene‐rich mineralogy, which is also evident in Mössbauer spectra and in normative mineralogy derived from bulk chemistry measured by the alpha particle X‐ray spectrometer. The correspondence of Bounce Rock’s chemical composition with the composition of certain basaltic shergottites, especially Elephant Moraine (EET) 79001 lithology B and Queen Alexandra Range (QUE) 94201, is very close, with only Cl, Fe, and Ti exhibiting deviations. Chemical analyses further demonstrate characteristics typical of Mars such as the Fe/Mn ratio and P concentrations. Possible shock features support the idea that Bounce Rock was ejected from an impact crater, most likely in the Meridiani Planum region. Bopolu crater, 19.3 km in diameter, located 75 km to the southwest could be the source crater. To date, no other rocks of this composition have been encountered by any of the rovers on Mars. The finding of Bounce Rock by the Opportunity rover provides further direct evidence for an origin of basaltic shergottite meteorites from Mars.     

A study of ordinary chondrites by Mössbauer spectroscopy with high‐velocity resolution

Abstract— An improvement in the velocity resolution and quality of Mössbauer spectra has been applied to a group of ordinary chondrites. This improvement permitted us to carry out a more detailed study of the iron bearing phases in these samples than has previously been possible. Mössbauer spectra of 11 ordinary chondrites of L and H chemical groups were measured using 4096 channels and presented for further analysis in 1024 channels. Subspectra of the metal grains of several chondrites demonstrated the presence of at least two magnetic sextets related to the main Fe(Ni, Co) phases. Moreover, Mössbauer study of extracted metal grains from Tsarev L5 revealed three sextets and one singlet spectral components related to various α‐Fe(Ni, Co), α‘‐Fe(Ni, Co), α₂‐Fe(Ni, Co), and γ‐Fe(Ni, Co) phases. Each subspectrum of olivine and pyroxene in Mössbauer spectra of ordinary chondrites was fitted by superposition of two quadrupole doublets related to M1 and M2 sites in minerals for the first time. An analysis of relative areas and Mössbauer hyperfine parameters was performed and some differences for L and H chondrites as well as for M1 and M2 sites were observed. Mössbauer parameters of troilite and oxidized iron were analyzed. In contrast to a previous study with 512‐channel spectra, the presence of oxidized iron was found in all chondrites.     

Bulk mineralogy,water abundance,and hydrogen isotope composition of unequilibrated ordinary chondrites

The origin and transport of water in the early Solar System is an important topic in both astrophysics and planetary science, with applications to protosolar disk evolution, planetary formation, and astrobiology. Of particular interest for understanding primordial water transport are the unequilibrated ordinary chondrites (UOCs), which have been affected by very limited alteration since their formation. Using X-ray diffraction and isotope ratio mass spectrometry, we determined the bulk mineralogy, H₂O content, and D/H ratios of 21 UOCs spanning from petrologic subtypes 3.00–3.9. The studied UOC falls of the lowest subtypes contain approximately 1 wt% H₂O, and water abundance globally decreases with increasing thermal metamorphism. In addition, UOC falls of the lowest subtypes have elevated D/H ratios as high as those determined for some outer Solar System comets. This does not easily fit with existing models of water in the protoplanetary disk, which suggest D/H ratios were low in the warm inner Solar System and increased radially. These new analyses confirm that OC parent bodies accreted a D-rich component, possibly originating from either the outer protosolar nebula or from injection of molecular cloud streamers. The sharp decrease of D/H ratios with increasing metamorphism suggests that the phase(s) hosting this D-rich component is readily destroyed through thermal alteration.     

Anomalous Mössbauer parameters in the second generation regolith Ghubara meteorite

Abstract— We conducted Mössbauer spectroscopic studies on the Ghubara meteorite which had been described as at least two‐generation regolith breccia on the macro scale. The isomer shift and quadrupole splitting of the Fe‐Ni part are quite different from those obtained in ordinary chondrites, reflecting shock effects. We observed a large amount of magnetite that may have come from weathering of, primarily, the silicate fraction. We found very similar iron mineralogy in the Densmore meteorite.     

Experimental shock metamorphism of the L4 ordinary chondrite Saratov induced by spherical shock waves up to 400 GPa

Abstract– We carried out shock experiments on macroscopic spherical samples of the L4 ordinary chondrite Saratov (natural shock stages S2–S3), using explosively generated spherical shock waves with maximum peak pressures of 400 GPa and shock‐induced temperatures >800 °C (up to several thousands °C). The evolution of shock metamorphism within a radius of the spherical samples was investigated using optical and scanning electron microscopy, microprobe and magnetic analyses as well as Mössbauer spectroscopy and X‐ray diffraction techniques. Petrographic analyses revealed a shock‐induced formation of three different concentric petrographic zones within the shocked samples: zone of total melting (I), zone of partial melting (II), and zone of solid‐state shock features (III). We found a progressive pressure‐induced oxidation of Fe‐Ni metal, whose degree increased with increasing shock peak pressure. The amount of FeO within zone I increased the factor of 1.4 with respect to its amount in the unshocked Saratov sample. This suggests that within zone I about 70 wt% of the initial metallic iron was oxidized, whereas magnetic analyses showed that about 10 wt% of it remained intact. This strongly supports the hypothesis that, in addition to oxidation, a migration of metallic iron from the central heavily shocked zone I toward less shocked peripheral zone took place as well (likely through shock veins where metallic droplets were observed). Magnetic analyses also showed a shock‐induced transformation of tetrataenite to taenite within all shocked subsamples, resulting in magnetic softening of these subsamples (decrease in remanent coercivity). These results have important implications for extraterrestrial paleomagnetism suggesting that due to natural impact processes, the buried crustal rocks of heavily cratered solid solar system bodies can have stronger remanent magnetism than the corresponding surface rocks.     

Analysis of ordinary chondrites using powder X‐ray diffraction: 2. Applications to ordinary chondrite parent‐body processes

Abstract– We evaluate the chemical and physical conditions of metamorphism in ordinary chondrite parent bodies using X‐ray diffraction (XRD)‐measured modal mineral abundances and geochemical analyses of 48 type 4–6 ordinary chondrites. Several observations indicate that oxidation may have occurred during progressive metamorphism of equilibrated chondrites, including systematic changes with petrologic type in XRD‐derived olivine and low‐Ca pyroxene abundances, increasing ratios of MgO/(MgO+FeO) in olivine and pyroxene, mean Ni/Fe and Co/Fe ratios in bulk metal with increasing metamorphic grade, and linear Fe addition trends in molar Fe/Mn and Fe/Mg plots. An aqueous fluid, likely incorporated as hydrous silicates and distributed homogeneously throughout the parent body, was responsible for oxidation. Based on mass balance calculations, a minimum of 0.3–0.4 wt% H₂O reacted with metal to produce oxidized Fe. Prior to oxidation the parent body underwent a period of reduction, as evidenced by the unequilibrated chondrites. Unlike olivine and pyroxene, average plagioclase abundances do not show any systematic changes with increasing petrologic type. Based on this observation and a comparison of modal and normative plagioclase abundances, we suggest that plagioclase completely crystallized from glass by type 4 temperature conditions in the H and L chondrites and by type 5 in the LL chondrites. Because the validity of using the plagioclase thermometer to determine peak temperatures rests on the assumption that plagioclase continued to crystallize through type 6 conditions, we suggest that temperatures calculated using pyroxene goethermometry provide more accurate estimates of the peak temperatures reached in ordinary chondrite parent bodies.     

Thermoluminescence sensitivity and thermal history of type 3 ordinary chondrites: Eleven new type 3.0–3.1 chondrites and possible explanations for differences among H,L, and LL chondrites

Abstract— We review induced thermoluminescence (TL) data for 102 unequilibrated ordinary chondrites (UOCs), many data just published in abstracts, in order to identify particularly primitive UOCs and further explore TL systematics that may have implications for the history of the chondrites and their parent body. We have identified 11 UOCs of petrologic types 3.0–3.1: Adrar 003, Elephant Moraine (EET) 90066, EET 90161, Grosvenor Mountains (GRO) 95502, Lewis Cliff (LEW) 88477, Meteorite Hills (MET) 96503, Yamato (Y)‐790787, Y‐791324, Y‐791558, Y‐793565, and Y‐793596. These samples represent an important new resource for researchers interested in the nature of primitive solar system materials. Previously reported trends in which TL sensitivity increases with TL peak temperature and TL peak width, which we interpret in terms of crystallization of feldspar in the ordered or disordered forms during metamorphism, are confirmed by the new data. Importantly, the present data strengthen the trend described earlier in which the mean level of metamorphism experienced by UOCs increases along the series LL, L and H. This suggests either different burial depths for the UOCs from each class, or formation at similar depths in regoliths of different thickness.     

Weathering in Antarctic H and CR chondrites: Quantitative analysis through Mössbauer spectroscopy

Abstract— Mössbauer spectroscopy is a very useful tool for identifying ferric iron weathering products in meteorites because of the capability to quantify the relative amounts of ferric iron in them. Mössbauer measurements were made of 33 Antarctic H chondrites (predominately H5) and two paired Antarctic CR chondrites. The primary goals of this study are to determine if Mössbauer spectroscopy can be used to determine which phases are weathering in Antarctic meteorites and if the relative amounts of ferric iron correlate with terrestrial age. Determining which minerals are weathering in ordinary chondrites appears very difficult due to variations in composition for different ordinary chondrites of the same meteorite class and possible problems in preparing homogeneous samples. The analysis of the two paired CR chondrites appears to indicate that metallic iron is predominately weathering to produce ferric iron for this class of meteorite. No correlation is seen between the relative amounts of ferric iron and terrestrial age for ordinary chondrites. One Antarctic H5 chondrite (ALHA77294) with a short ¹⁴C age of 135 ± 200 years from the dating of interior carbonate weathering products does have a relatively low amount of ferric iron, which is consistent with this meteorite being exposed on the surface for a relatively short time.     

An overlooked fragment of the Santa Catharina ataxite

Abstract— An undocumented mass of 28 kg, recovered from a museum collection, is examined by several methods: optical microscopy, scanning electron microscopy, X-ray diffraction, Mössbauer spectroscopy and chemical analyses by atomic absorption, energy- and wavelength-dispersive X-ray spectrometry and, with respect to the trace elements Ir, As, Au, by neutron activation. The structure and the mineralogical chemical composition of the mass identify it as a fragment of the Santa Catharina iron meteorite from Brazil.     

Characterization of Mason Gully (H5): The second recovered fall from the Desert Fireball Network

Mason Gully, the second meteorite recovered using the Desert Fireball Network (DFN), is characterized using petrography, mineralogy, oxygen isotopes, bulk chemistry, and physical properties. Geochemical data are consistent with its classification as an H5 ordinary chondrite. Several properties distinguish it from most other H chondrites. Its 10.7% porosity is predominantly macroscopic, present as intergranular void spaces rather than microscopic cracks. Modal mineralogy (determined via PS‐XRD, element mapping via energy dispersive spectroscopy [EDS], and X‐ray tomography [for sulfide, metal, and porosity volume fractions]) consistently gives an unusually low olivine/orthopyroxene ratio (0.67?0.76 for Mason Gully versus ~1.3 for typical H5 ordinary chondrites). Widespread “silicate darkening” is observed. In addition, it contains a bright green crystalline object at the surface of the recovered stone (diameter ≈ 1.5 mm), which has a tridymite core with minor α‐quartz and a rim of both low‐ and high‐Ca pyroxene. The mineralogy allows the calculation of the temperatures and ?(O₂) characterizing thermal metamorphism on the parent body using both the two‐pyroxene and the olivine‐chromite geo‐oxybarometers. These indicate that MG experienced a peak metamorphic temperature of ~900 °C and had a similar ?(O₂) to Kernouvé (H6) that was buffered by the reaction between olivine, metal, and pyroxene. There is no evidence for shock, consistent with the observed porosity structure. Thus, while Mason Gully has some unique properties, its geochemistry indicates a similar thermal evolution to other H chondrites. The presence of tridymite, while rare, is seen in other OCs and likely exogenous; however, the green object itself may result from metamorphism.     

Mössbauer spectroscopic studies of the Piplia Kalan (eucrite) and Lohawat (howardite) meteorites

Abstract— Two meteorites belonging to the howardite‐eucrite‐diogenite (HED) group fell recently in Rajasthan, India. One of these, Piplia Kalan, was classified as a eucrite and the other, Lohawat, as a howardite. In this study, we present the results of Mössbauer spectroscopic investigations of these two meteorites. We also compare the results with the Mössbauer experiments reported for the Kapoeta howardite and look for systematics in the Mössbauer spectra of HED meteorites.