THE MINERALOGY OF METEORITES

During the past decade the number of minerals recognized in meteorites has doubled, from about 40 in 1962 to over 80 in 1972. The great expansion in our knowledge can be largely ascribed to the introduction of the electron-beam microprobe as a research tool, enabling the quantitative analysis of microscopic grains in polished sections. While most of these discoveries are of minerals present in minute amounts, their identification has elucidated many aspects of meteorite formation. Of particular interest are five phosphate minerals, three of them unknown in terrestrial rocks; a chromium nitride and a silicon oxynitride; lonsdaleite and chaoite, new polymorphs of carbon; ringwoodite and majorite, the spinel and garnet analogs of olivine and pyroxene respectively; a number of calcium- and aluminum-rich silicates in the Allende meteorite, a Type III carbonaceous chondrite which fell in 1969; and several alkali-rich silicates found as inclusions in iron meteorites. Knowledge of the compositional range of the common minerals olivine, pyroxene, and plagioclase has also been greatly increased by recent researches     

THE HAVERÖ UREILITE*

The Haverö ureilite fell on August 2, 1971 on the Island of Haverö, Finland, lat 22° 03‘ 43“ E., long 60° 14’ 44” N. The meteorite contains curved open fractures partly filled with kamacite foils or drops, clusters of olivine mosaic with preferred orientation, very fine-lamellar polysynthetic twinned clino-***bronzite and carbonaceous matter as laths up to 4 mm in length. The carbon laths are in preferred orientation and contain in addition to graphite, kamacite, chromite and diamonds. The petrology, textural features and origin are discussed.     

ARGON-37, ARGON-39, AND TRITIUM RADIOACTIVITIES IN THE HAVERÖ METEORITE

The ³⁷Ar and ³⁹Ar radioactivities were measured in a dissolved and in a melted sample of Haverö. The ³⁷Ar in the metal was 12.4 ± 2.6 dpm/kg (Fe + Ni). The ³⁹Ar in the metal was 49.3 ± 5.5 dpm/kg (Fe + Ni). The ³⁷Ar activity is within 30 percent of that in the Lost City meteorite, while the ³⁹Ar activity is a factor of two higher than in Lost City. The similarity in the ³⁷Ar activities of the metal of the two meteorites indicates that these two bodies had similar preatmospheric sizes. The higher ³⁹Ar activity in the metal of Haverö indicates that the aphelion of Haverö's orbit was at least 4.3 A.U. The ³H radioactivity in Haverö was measured to be 415 ± 30 dpm/kg. The ³H activity combined with the ³He content gives a ³He/2³H exposure age for Haverö of (29.5 ± 2.5) X ⁶10 years.     

MORPHOLOGIES OF IRON CRYSTALS FROM THE HAVERÖ METEORITE

Studies of unpolished chips of the Haverö meteorite using the scanning electron microscope (SEM) and the electron microprobe (EMP), show two types of metallic iron particles: A, discrete convex globules of 5 to 50 microns made up of lamellae and interlocked grains, evenly interspersed among the matrix; B, flattened contorted crystals, less than one micron, lining the iron globules and cavities in the silicates or forming rounded spiny bodies. This second type of iron is interpreted, according to the current theory, as resulting from the in situ reduction of iron-magnesium silicates     

THE CHEMICAL COMPOSITION OF THE HAVERÖ METEORITE AND THE GENESIS OF THE UREILITES

The chemical composition of Haverö is presented and compared with the composition of the other five ureilites     

Mineralogy of meteorite groups

Abstract— Approximately 275 mineral species have been identified in meteorites, reflecting diverse redox environments, and, in some cases, unusual nebular formation conditions. Anhydrous ordinary, carbonaceous and R chondrites contain major olivine, pyroxene and plagioclase; major opaque phases include metallic Fe-Ni, troilite and chromite. Primitive achondrites are mineralogically similar. The highly reduced enstatite chondrites and achondrites contain major enstatite, plagioclase, free silica and kamacite as well as nitrides, a silicide and Ca-, Mg-, Mn-, Na-, Cr-, K- and Ti-rich sulfides. Aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates, complex organic compounds, magnetite, various sulfates and sulfides, and carbonates. In addition to kamacite and taenite, iron meteorites contain carbides, elemental C, nitrides, phosphates, phosphides, chromite and sulfides. Silicate inclusions in IAB/IIICD and IIE iron meteorites consist of mafic silicates, plagioclase and various sulfides, oxides and phosphates. Eucrites, howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides. Ureilites are made up mainly of calcic, chromian olivine and low-Ca clinopyroxene embedded in a carbonaceous matrix; accessory phases include the C polymorphs graphite, diamond, lonsdaleite and chaoite as well as metallic Fe-Ni, troilite and halides. Angrites are achondrites rich in fassaitic pyroxene (i.e., Al-Ti diopside); minor olivine with included magnesian kirschsteinite is also present. Martian meteorites comprise basalts, lherzolites, a dunite and an orthopyroxenite. Major phases include various pyroxenes and olivine; minor to accessory phases include various sulfides, magnetite, chromite and Ca-phosphates. Lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase. Several meteoritic phases were formed by shock metamorphism. Martensite (α₂-Fe,Ni) has a distorted body-centered-cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling. The C polymorphs diamond, lonsdaleite and chaoite formed by shock from graphite. Suessite formed in the North Haig ureilite by reduction of Fe and Si (possibly from olivine) via reaction with carbonaceous matrix material. Ringwoodite, the spinel form of (Mg,Fe)₂SiO₄, and majorite, a polymorph of (Mg,Fe)SiO₃ with the garnet structure, formed inside shock veins in highly shocked ordinary chondrites. Secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic Fe-Ni by oxidation, phosphates formed by the alteration of schreibersite, and sulfates formed by alteration of troilite.     

THE CHEMISTRY OF HAVERÖ UREILITE

The concentrations of 41 major, minor and trace elements were determined in Haverö ureilite. In addition to the analysis on bulk samples a number of separates were measured, too, including hand-picked samples of the dark carbonaceous, diamond-rich inclusions and two metal fractions. It was found that one metal fraction had an extraordinarily high Ir/Au-ratio of 19. According to the concentrations of the noble metals and of nickel, gallium, tungsten and rhenium this metal represents, most probably, the siderophile portion of a high temperature condensate, i.e., the pattern of these elements is very similar to that found in Allende inclusions (Wänke et al., 1972)     

ELEMENTAL ABUNDANCES IN THE HAVERÖ METEORITE

Abundances of 15 major, minor and trace elements have been determined in powders and interior chips derived from the Haverö ureilite. The values are in close agreement with mean values for other ureilites, as reported in the literature. The powdered samples exhibited slightly higher abundances of O and Si, than the interior chips. It is suggested that this may be due to alteration of the samples during the powdering process     

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.     

COSMOGENEIC RADIONUCLIDES IN THE HAVERÖ METEORITE

An 87-gram sample of the Haverö ureilite has been analyzed by non-destructive gamma-ray spectrometry. The results of the measurements, in dpm/kg at time of fall, are: ²²Na, 71 ± 3; ²⁶Al, 43 ± 3; ⁴⁶Sc, 3.4 ± 2.1; ⁵⁴Mn, 35 ± 6; ⁶⁰Co, 0.7, 2*** limit. Haverö has 77 ± 14% of the ²⁶Al activity calculated for its chemical composition. When averaged with previously-reported analyses of Goalpara and Novo Urei, ureilites as a class have 74 ± 7% of their expected ²⁶Al activity. The depletion in ²⁶Al could be the coincidental result of identical “shielding” effects in three meteorites of apparently very different preatmospheric sizes. Alternatively, ureilites may have been exposed to a lower cosmic-ray flux than that experienced by most chondrites, probably the result of characteristically different orbits     

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.     

The New Peruvian Meteorite Carancas: Mössbauer Spectroscopy and X-Ray Diffraction Studies

The Carancas meteorite fell on 15 September 2007 approximately 10 km south of Desaguadero, near Lake Titicaca, Peru, producing bright lights, clouds of dust in the sky and intense detonations. The Carancas meteorite is classified as a H4–5 ordinary chondrite with shock stage S3 and a degree of weathering W0. The Carancas meteorite is characterized by well defined chondrules composed either of olivine or pyroxene. The Mössbauer spectra show an overlapping of paramagnetic and magnetic phases. The spectra show two quadrupole doublets associated to olivine and pyroxene; and two magnetic sextets, associated with the primary phases kamacite/taenite and Troilite (Fe²⁺). Metal particles were extracted from the bulk powdered samples exhibit only kamacite and small amounts of the intergrowth tetrataenite/antitaenite. X-Ray diffractogram shows the primary phases olivine, pyroxene, troilite, kamacite, diopside and albite. Iron oxides has not been detected by Mössbauer spectroscopy or XRD as can be expected for a meteorite immediately recovered after its fall.     

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.     

Chemical and genetic characterization of the ungrouped pallasite Lieksa

The meteorite Lieksa was found in 2017 in Löpönvaara, Finland, and later donated to the Finnish Museum of Natural History. Here, we report siderophile element concentrations, genetic isotopic data, and a metal–silicate segregation age for the meteorite. The ~280 g Lieksa is ~80% metal and ~20% silicate and oxide inclusions by volume, with the inclusions consisting primarily of Fe-rich olivine. Due to Lieksa's silicate content, coupled with a texture characterized by metal enclosing the silicates, it has been classified as a pallasite. Lieksa's olivine and bulk chemical characteristics are distinct from those of the known pallasite and iron meteorite groups, consistent with its classification as ungrouped. The meteorite exhibits a flat, chondrite-normalized highly siderophile element pattern, consistent with an origin as an early crystallization product from a metallic melt with chondritic relative abundances. Molybdenum, Ru, and ¹⁸³W isotopic data indicate that Lieksa formed in the non-carbonaceous (NC) domain of the solar nebula. Radiogenic ¹⁸²W abundances for Lieksa yield a model metal–silicate segregation age of 1.5 ± 0.8 Myr after calcium-aluminum-rich inclusion formation, which is within the range established for other NC-type pallasite and iron meteorite parent bodies.     

New insights into the mineralogy and weathering of the Meridiani Planum meteorite,Mars

Meridiani Planum is the first officially recognized meteorite find on the surface of Mars. It was discovered at and named after the landing site of the Mars Exploration Rover Opportunity. Based on its composition, it was classified as a IAB complex iron meteorite. Mössbauer spectra obtained by Opportunity are dominated by kamacite (α‐Fe‐Ni) and exhibit a small contribution of ferric oxide. Several small features in the spectra have been neglected to date. To shed more light on these features, five iron meteorite specimens were investigated as analogs to Meridiani Planum with a laboratory Mössbauer setup. Measurements were performed on (1) their metallic bulk, (2) troilite (FeS) inclusions, (3) cohenite ((Fe,Ni,Co)₃C) and schreibersite ((Fe,Ni)₃P), and (4) corroded rims. In addition to these room‐temperature measurements, a specimen from the Mundrabilla IAB‐ungrouped meteorite was measured at Mars‐equivalent temperatures. Based on these measurements, the features in Meridiani Planum spectra can be explained with the presence of small amounts of schreibersite and/or cohenite and iron oxides. The iron oxides can be attributed to a previously reported coating on Meridiani Planum. Their presence indicates weathering through the interaction of the meteorite with small amounts of water.     

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.     

Noble gases in fossil micrometeorites and meteorites from 470 Myr old sediments from southern Sweden,and new evidence for the L‐chondrite parent body breakup event

Abstract— We present noble gas analyses of sediment‐dispersed extraterrestrial chromite grains recovered from ?470 Myr old sediments from two quarries (Hällekis and Thorsberg) and of relict chromites in a coeval fossil meteorite from the Gullhögen quarry, all located in southern Sweden. Both the sediment‐dispersed grains and the meteorite Gullhögen 001 were generated in the L‐chondrite parent body breakup about 470 Myr ago, which was also the event responsible for the abundant fossil meteorites previously found in the Thorsberg quarry. Trapped solar noble gases in the sediment‐dispersed chromite grains have partly been retained during ?470 Myr of terrestrial residence and despite harsh chemical treatment in the laboratory. This shows that chromite is highly retentive for solar noble gases. The solar noble gases imply that a sizeable fraction of the sediment‐dispersed chromite grains are micrometeorites or fragments thereof rather than remnants of larger meteorites. The grains in the oldest sediment beds were rapidly delivered to Earth likely by direct injection into an orbital resonance in the inner asteroid belt, whereas grains in younger sediments arrived by orbital decay due to Poynting‐Robertson (P‐R) drag. The fossil meteorite Gullhögen 001 has a low cosmic‐ray exposure age of ?0.9 Myr, based on new He and Ne production rates in chromite determined experimentally. This age is comparable to the ages of the fossil meteorites from Thorsberg, providing additional evidence for very rapid transfer times of material after the L‐chondrite parent body breakup.     

On the occurrence and origin of anthropogenic radionuclides found in a fragment of the Chelyabinsk (LL5) meteorite

A piece of the 2013 Chelyabinsk meteorite was investigated for its content of anthropogenic radionuclides. In addition to traces of cesium‐137 that had been previously reported for this particular fragment, we found an unusually high amount of strontium‐90, which indicates that the source of this contamination was the Kyshtym accident (1957). A high Sr‐90/Cs‐137 activity ratio is characteristic for Kyshtym‐derived contaminations. Based on the cesium‐137 content in the soil from the finding site, it is estimated that the fragment was contaminated with soil particles in the milligram range upon impact. Investigation of the soil revealed very unusual ferromagnetic characteristics and an iron‐rich chemical composition. Mössbauer spectroscopy indicated the presence of steel components in this soil, suggesting that the investigated meteorite fragment was found in an industrial dumping site rather than natural soil.     

A NEW SPECIMEN OF THE MOUNT DOOLING IRON METEORITE FROM MOUNT MANNING,WESTERN AUSTRALIA

A 701 kg iron meteorite has recently been discovered near the Mount Manning Range in Western Australia. The meteorite has a fan-shaped or delta wing configuration, one side being smooth and slightly concave with a well-defined fusion crust, whilst the other side is rough, convex and possesses numerous regmaglypts. It is probable that the meteorite pentrated much of the earth's atmosphere in an aerodynamically stable orientation, typical of the stalled attitude of delta wing aircraft. The meteorite is a member of Chemical Group 1C. A comparison of the chemical composition, surface features, microstructure and location of this meteorite with the Mount Dooling meteorite confirms that the find is a larger specimen of Mount Dooling. It is possible that other fragments of the Mount Dooling meteorite may be found in the Mount Manning Range region.     

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.