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.     

Fe Mössbauer spectroscopy as a tool in astrobiology

The element Fe and Fe-bearing minerals occur ubiquitously throughout the field of astrobiology. Cycling between the various oxidation states of Fe provides a source of energy available for life. Banded iron formations may record the rise of oxygenic photosynthesis. The distribution of Fe between Fe-bearing minerals and its oxidation states can help to characterize and understand ancient environments with respect to the suitability for life by constraining the primary rock type and the redox conditions under which it crystallized, the extent of alteration and weathering, the type of alteration and weathering products, and the processes and environmental conditions for alteration and weathering. Fe Mössbauer spectroscopy is a powerful tool to investigate Fe-bearing compounds. It can identify Fe-bearing minerals, determine Fe oxidation states with high accuracy, quantify the distribution of Fe between mineralogical phases, and provide clues about crystallinity and particle sizes. Two miniaturized Mössbauer spectrometers are on board of the NASA Mars Exploration Rovers Spirit and Opportunity. The Fe-bearing minerals goethite, an iron oxide-hydroxide, and jarosite, an iron hydroxide sulfate, were identified by Mössbauer spectroscopy in Gusev Crater and at Meridiani Planum, respectively, providing in situ proof of an aqueous history of the two landing sites and constraints on their habitability. Hematite identified by Mössbauer spectroscopy at both landing sites adds further evidence for an aqueous history. On Earth, Mössbauer spectroscopy was used to monitor possibly microbially-induced changes of Fe-oxidation states in basaltic glass samples exposed at the Loihi Seamount, a deep sea hydrothermal vent system, which might be analogous to possible extraterrestrial habitats on ancient Mars or the Jovian moon Europa today.     

Systematics of Mössbauer absorption areas in ordinary chondrites and applications to a newly fallen meteorite in Jodhpur,India

Abstract— Mössbauer absorption areas corresponding to ⁵⁷Fe in olivine, pyroxene, troilite, and the metallic phase in ordinary chondrites are shown to exhibit certain systematic behaviors. H chondrites occupy 2 distinct regions on the plot of metallic phase absorption area versus silicate absorption area, while L/LL chondrites fall in a separate region. Similar separation is also observed when pyroxene absorption area is plotted against olivine absorption area. The one‐dimensional plot for the ratio of olivine area to pyroxene area separates L and LL chondrites. Based on these systematics, a newly fallen meteorite at Jodhpur, India is suggested to be an LL chondrite.     

Axtell and Allende: A Mössbauer spectroscopic study

Abstract— Mössbauer spectra showed the CV3 oxidized subgroup meteorites Allende and Axtell to be similar in olivine content and in a surprising lack of pronounced magnetic components, but different in Fe³⁺ phases. One atypical Allende sample showed an 8% area under the curve for magnetite, which is still less than a reported value for a CV3 reduced subgroup member. Allende's unusual Fe³⁺ spectral region distinguishes it from most other stony meteorites and is difficult to fit to known mineral parameters.     

Mössbauer study of Meridiani Planum,the first iron‐nickel meteorite found on the surface of Mars by the MER Opportunity

Abstract— –Meridiani Planum is the first iron meteorite found on Mars. It was discovered in 2005 by the Mars Exploration Rover Opportunity (MER‐B). Mössbauer spectra (MS) of the unbrushed and brushed meteorite species were acquired in 10 degrees temperature windows in the range of 210–260 K. Earlier examinations of these MS have led to the conclusion that the meteorite, which contains ～～7 wt% Ni, belongs to the IAB meteorite group. Here, making use of a recently developed calibration/folding procedure for MER MS, we report the results of the MS analyses for the single temperature windows m5 (210–220 K), m6 (220–230 K), m7 (230–240 K), and m89 (240–260 K). All spectra consist of a sextet and a ferric doublet. The hyperfine field of the sextet, extrapolated to room temperature, is ～～34.5 T, which is, based on Mössbauer studies of meteorites found on Earth, indeed consistent with the presence of kamacite. The fractional spectral area of the sextet is ～～0.96 of the total spectrum. The ferric doublet has an average quadrupole splitting of 0.70 mm/s and is not diagnostic of any specific Fe mineral.     

Druse clinopyroxene in D'Orbigny angritic meteorite studied by single‐crystal X‐ray diffraction,electron microprobe analysis,and Mössbauer spectroscopy

Abstract— The crystal structure of druse clinopyroxene from the D'Orbigny angrite, (Ca_0.944 Fe²⁺_0.042 Mg_0.010Mn_0.004) (Mg_0.469Fe²⁺_0.317Fe³⁺_0.035Al_0.125Cr_0.010Ti_0.044) (Si_1.742Al_0.258) O₆, a = 9.7684(2), b = 8.9124(2), c = 5.2859(1) Å, β = 105.903(1)°, V = 442.58 ų, space group C2/c, Z = 2, has been refined to an R₁ index of 1.92% using single‐crystal X‐ray diffraction data. The unit formula, calculated from electron microprobe analysis, and the refined site scattering values were used to assign site populations. The distribution of Fe²⁺and Mg over the M1 and M2 sites suggests a closure temperature of 1000 °C. Mössbauer spectroscopy measurements were done at room temperature on a single crystal and a powdered sample. The spectra are adequately fit by a Voigt‐based quadrupole‐splitting distribution model having two generalized sites, one for Fe²⁺with two Gaussian components and one for Fe³⁺with one Gaussian component. The two ferrous components are assigned to Fe²⁺at the M1 site, and arise from two different next‐nearest‐neighbor configurations of Ca and Fe cations at the M2 site: (3Ca,0Fe) and (2Ca,1Fe). The Fe³⁺/Fe_tot ratio determined by Mössbauer spectroscopy is in agreement with that calculated from the electron microprobe analysis. The results are discussed in connection with the redox and thermal history of D'Orbigny.     

Rapid weathering in Holbrook: An iron-57 Mössbauer spectroscopy study

Abstract— Samples of Holbrook (an L6 chondrite that fell in Arizona in 1912) were analysed by ⁵⁷Fe Mössbauer spectroscopy to determine the proportion of the total Fe that had been converted to Fe³⁺ by weathering processes. Although samples recovered in 1912 showed negligible (<1%) alteration, a spectrum recorded from a specimen recovered in 1968 showed that 9.7% of the total Fe was present as Fe³⁺. Given the existence of samples in similar semiarid environments with terrestrial ages >40 ka, a linear rate of weathering is unrealistic, rapidly producing very high levels of oxidation in samples with low terrestrial ages. However if weathering follows an approximate power law, then we can model a rapid initial phase and the levels of oxidation that are more typical in samples with much longer terrestrial residence times recovered from Roosevelt County. Our analysis, together with work on terrestrial age dated samples, indicates that hot desert weathering of ordinary chondrites is at least a two-stage process, with an initial rapid phase lasting <500 years before oxidation is passivated.     

Mineralogy and 57Fe Mössbauer spectroscopy of opaque phases in the Neuschwanstein EL6 chondrite

Abstract— This study presents compositional data and ⁵⁷Fe Mössbauer spectra, taken at 295 K and 85 K, of two fragments of the enstatite (EL6) chondrite Neuschwanstein that fell near the famous Neuschwanstein castle (Bavaria, southern Germany) on April 6, 2002. Main silicate minerals are enstatite (Fs 2) and plagioclase (An 20), the main opaque minerals are kamacite and troilite. Small amounts of oldhamite, daubreelite, and schreibersite have been found. The presented Mössbauer data are the first data gathered for an EL6 chondrite. The dominant parts of each Mössbauer spectrum consist of two six‐line patterns due to the presence of ferromagnetic phases kamacite and troilite. In contrast to other chondrites, peaks of other iron species in the central parts of the spectra are missing due to an extremely low content of Fe‐bearing paramagnetic components. The hyperfine interaction parameters for kamacite are internal magnetic hyperfine field H_hf = 333.2 kOe, isomer shift (relative to a metallic Fe foil) IS = 0.01 mm/s, quadrupole splitting QS = 0 mm/s, line width W = 0.41 mm/s. The data for troilite are H_hf = 305.5 kOe, IS = 0.75 mm/s, QS = ?0.85 mm/s, W = 0.34 mm/s.     

The irradiation history of the Ghubara (L5) regolith breccia

Abstract— We measured cosmic‐ray products—noble gases, radionuclides, thermoluminescence, and nuclear tracks—and trace element contents and mineralogy of samples of three orthogonal and mutually intersecting cores (41–46 cm long) of a 101.6 kg Ghubara individual (1958,805) at The Natural History Museum, London. The xenoliths, like the host, have high concentrations of trapped solar gases and are heavily shocked. While contents of noble gases and degree of shock‐loading in this individual and three others differ somewhat, the data indicate that Ghubara is a two‐generation regolith breccia. Contents of cosmogenic ²⁶Al and ¹⁰Be and low track densities indicate that the Ghubara individuals were located more than 15 cm below the surface of an 85 cm meteoroid. Because of its large size, Ghubara's cosmic‐ray exposure age is poorly defined to be 15–20 Ma from cosmogenic nuclides. Ghubara's terrestrial age, based on ¹⁴C data, is 2–3 ka. Not only is Ghubara the first known case of a two‐generation regolith breccia on the macroscale, it also has a complicated thermal and irradiation history.     

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.     

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.     

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.     

A high spatial resolution synchrotron Mössbauer study of the Tazewell IIICD and Esquel pallasite meteorites

Metallic phases in the Tazewell IIICD iron and Esquel pallasite meteorites were examined using ⁵⁷Fe synchrotron Mössbauer spectroscopy. Spatial resolution of ~10–20 μm was achieved, together with high throughput, enabling individual spectra to be recorded in less than 1 h. Spectra were recorded every 5–10 μm, allowing phase fractions and hyperfine parameters to be traced along transects of key microstructural features. The main focus of the study was the transitional region between kamacite and plessite, known as the “cloudy zone.” Results confirm the presence of tetrataenite and antitaenite in the cloudy zone as its only components. However, both phases were also found in plessite, indicating that antitaenite is not restricted exclusively to the cloudy zone, as previously thought. The confirmation of paramagnetic antitaenite as the matrix phase of the cloudy zone contrasts with recent observations of a ferromagnetic matrix phase using X‐ray photoemission electron spectroscopy. Possible explanations for the different results seen using these techniques are proposed.     

Glassy magnetic cronstedtite signatures in Mukundpura CM2 chondrite based on magnetic and Mössbauer studies

We have studied the Mukundpura CM2 meteorite for magnetic properties as a function of temperature and magnetic field, as well as its Mössbauer spectrum, at room and low temperatures (up to 5 K). We find that the high temperature paramagnetic phase is followed by two magnetic transitions: a weak transition near 125 K and a strong transition at 8 K. The weak (125 K) magnetic phase can be attributed to complex Fe²⁺–Fe³⁺ constituents present in the meteorite. The absence of the characteristic sextet corresponding to magnetite in Mossbauer spectrum indicates that this magnetic phase is not magnetite, which, if present, must be in insignificant amount. The 8 K magnetic ordering is superimposed with weak ferromagnetic ordering, showing spin‐glass transition. The Mössbauer spectrum taken at 5 K substantiates the observed spin‐glassy nature, as very large hyperfine field ~32 T is recorded, causing localized subordering leading to spin‐glass behavior. The Mössbauer spectra also confirm that iron is mainly present in serpentine‐group minerals, both in ferrous and ferric states. The complete serpentinization of basic silicates indicates aggressive hydrous alteration. These results show that the observed spin‐glass signature is a characteristic feature of the cronstedtite phase in CM meteorites. This feature is unique to carbonaceous CM chondrites and could be used for nondestructive, quick, and independent classification of this rare class of meteorites. Furthermore, the absence of olivine and the presence of cronstedtite in Mossbauer spectra show that the degree of aqueous alteration observed is the most severe in Mukundpura CM2 meteorite, as compared to many other CM2 meteorites. The degree of aqueous alteration in CM2 carbonaceous chondrites increases in the sequence: Paris, Murchison, Murray, Mighei, Nogoya, Cold Bokkeveld, and Mukundpura.     

MÖssbauer spectroscopy,x-ray diffraction,and electron microprobe analysis of the New Haifa meteorite

Abstract— MÖssbauer spectroscopy, x-ray diffraction (XRD) measurements, and electron microprobe analysis (EMPA) have been carried out for the investigation of a newly fallen Sudanese meteorite named New Haifa. The room temperature MÖssbauer spectrum is fitted with three sextets and two doublets. The sextets are assigned to Fe in troilite, kamacite, and taenite, and the two doublets are assigned to Fe²⁺in olivine and pyroxene (no Fe³⁺was found). The microprobe trace of Ni concentration across a kamacite-taenite-kamacite area shows a high-Ni concentration at the interfaces between kamacite and taenite. From the microprobe analysis, olivine appears to have a constant composition, whereas pyroxene has a varying composition. The mole fractions of the Fe end members of olivine (fayalite) and pyroxene (ferrosilite) are found to be 23.5% and 23.2%, respectively. Accordingly, the New Haifa meteorite is classified as an ordinary L-type chondrite.     

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.     

The regolith portion of the lunar meteorite Sayh al Uhaymir 169

Abstract— –Sayh al Uhaymir (SaU) 169 is a composite lunar meteorite from Oman that consists of polymict regolith breccia (8.44 ppm Th), adhering to impact‐melt breccia (IMB; 32.7 ppm Th). In this contribution we consider the regolith breccia portion of SaU 169, and demonstrate that it is composed of two generations representing two formation stages, labeled II and III. The regolith breccia also contains the following clasts: Ti‐poor to Ti‐rich basalts, gabbros to granulites, and incorporated regolith breccias. The average SaU 169 regolith breccia bulk composition lies within the range of Apollo 12 and 14 soil and regolith breccias, with the closest correspondence being with that of Apollo 14, but Sc contents indicate a higher portion of mare basalts. This is supported by relations between Sm‐Al₂O₃, FeO‐Cr₂O₃‐TiO₂, Sm/Eu and Th‐K₂O. The composition can best be modeled as a mixture of high‐K KREEP, mare basalt and norite/troctolite, consistent with the rareness of anorthositic rocks. The largest KREEP breccia clast in the regolith is identical in its chemical composition and total REE content to the incompatible trace‐element (ITE)‐ rich high‐K KREEP rocks of the Apollo 14 landing site, pointing to a similar source. In contrast to Apollo 14 soil, SaU 169 IMB and SaU 169 KREEP breccia clast, the SaU 169 regolith is not depleted in K/Th, indicating a low contribution of high‐Th IMB such as the SaU 169 main lithology in the regolith. The data presented here indicate the SaU 169 regolith breccia is from the lunar front side, and has a strong Procellarum KREEP Terrane signature.     

He and Ne in individual chromite grains from the regolith breccia Ghubara (L5): Exploring the history of the L chondrite parent body regolith

We analyzed He and Ne in chromite grains from the regolith breccia Ghubara (L5), to compare it with He and Ne in sediment‐dispersed extraterrestrial chromite (SEC) grains from mid‐Ordovician sediments. These SEC grains arrived on Earth as micrometeorites in the aftermath of the L chondrite parent body (LCPB) breakup event, 470 Ma ago. A significant fraction of them show prolonged exposure to galactic cosmic rays for up to several 10 Ma. The majority of the cosmogenic noble gases in these grains were probably acquired in the regolith of the LCPB (Meier et al. 2010 ). Ghubara, an L chondritic regolith breccia with an Ar‐Ar shock age of 470 Ma, is a sample of that regolith. We find cosmic‐ray exposure ages of up to several 10 Ma in some Ghubara chromite grains, confirming for the first time that individual chromite grains with such high exposure ages indeed existed in the LCPB regolith, and that the >10 Ma cosmic‐ray exposure ages found in recent micrometeorites are thus not necessarily indicative of an origin in the Kuiper Belt. Some Ghubara chromite grains show much lower concentrations of cosmogenic He and Ne, indicating that the 4π (last‐stage) exposure age of the Ghubara meteoroid lasted only 4–6 Ma. This exposure age is considerably shorter than the 15–20 Ma suggested before from bulk analyses, indicating that bulk samples have seen regolith pre‐exposure as well. The shorter last‐stage exposure age probably links Ghubara to a small peak of ⁴⁰Ar‐poor L5 chondrites of the same exposure age. Furthermore, and quite unexpectedly, we find a Ne component similar to presolar Ne‐HL in the chromite grains, perhaps indicating that some presolar Ne can be preserved even in meteorites of petrologic type 5.     

Ferric iron in SNC meteorites as determined by Mössbauer spectroscopy: Implications for martian landers and martian oxygen fugacity

Abstract— Mössbauer spectra of martian meteorites are currently of great interest due to the Mössbauer spectrometers on the Athena mission MER rovers as well as the European Space Agency Mars Express mission, with its Beagle 2 payload. Also, considerable current effort is being made to understand the oxygen fugacity of martian magmas because of the effect of fO₂ on mineral chemistry and crystallization processes. For these 2 reasons, the present study was conceived to acquire room temperature Mössbauer spectra of mineral separates and whole rock samples of 10 SNC meteorites. The results suggest that mineral identification using remote application of this technique will be most useful when the phases present have distinctive parameters arising from Fe in very different coordination polyhedra; for example, pyroxene coexisting with olivine can be discriminated easily, but opx versus cpx cannot. The MER goal of using Mössbauer spectroscopy to quantify the relative amounts of individual mineral species present will be difficult to satisfy if silicates are present because the lack of constraints on wt% FeO contents of individual silicate phases present will make modal calculations impossible. The remote Mössbauer spectroscopy will be most advantageous if the rocks analyzed are predominantly oxides with known stoichiometries, though these phases are not present in the SNCs. As for the detection of martian oxygen fugacity, no evidence exists in the SNC samples studied of a relationship between Fe³⁺ content and fO₂ as calculated by independent methods. Possibly, all of the Fe³⁺ observed in olivine is the result of dehydrogenation rather than oxidation, and this process may also be the source of all the Fe³⁺ observed in pyroxene. The observed Fe³⁺ in pyroxene also likely records an equilibrium between pyroxene and melt at such low fO₂ that little or no Fe³⁺ would be expected.     

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.