First recorded find of ordinary chondrite material in the Kaidun meteorite

For the first time, ordinary chondrite material—the most common type among the present-day fall meteorite—has been found in the unique Kaidun breccia. The discovered object is a large unequilibrated olivine-pyroxene porphyritic chondrule, with peripheral and central zones of different structures, suggesting different crystallization regimes. In chemical composition, the chondrule corresponds to unequilibrated ordinary chondrites of petrological type 3; it is enriched in lithophile elements and depleted in siderophiles, indicating formation by melting of the parent material, which preceded or was accompanied by metal-silicate fractionating. The chondrule material was subjected to aqueous alteration that formed smectite and calcite in the cavities and veins of its central part. The anomalous oxygen isotopic compositions of the chondrule are evidence of an oxygen reservoir different from known types of meteorites, including the ordinary-chondrite chondrules. Thus, the unique breccia Kaidun contains ordinary chondrite material along with carbonaceous and enstatite chondrite material, products of early nebular processes, and highly differentiated planetary-type material.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 2, 2005, pp. 169–176.Original Russian Text Copyright © 2005 by Ivanova, Kononkova, Ivanov.     

The Kaidun meteorite: Mineralogy of an unusual CM1 lithology

Abstract Kaidun is a breccia of disparate enstatite and carbonaceous chondrite clasts that continues to provide real surprises. Many Kaidun clasts have been intensely altered by aqueous fluids, as evidenced by the widespread occurrence of ferromagnesian phyllosilicates and by the presence of carbonate- and phyllo-silicate-filled veins. In this report, we describe an unusual CM lithology containing many mineralogical features not previously reported from any meteorite, including pyrrhotite, with exclusive needlelike morphologies and thick mantles of phyllosilicate, and complex aggregates of phyllosilicate, melanite garnet, crosscut by pentlandite veins. The latter features appear to be due in large part to extensive hydrothermal alteration at temperatures on the order of 450 °C, which is significantly higher than that attained during secondary processing from other known CM material.     

Lewis Cliff 87223, an anomalous enstatite chondrite and the diversity of enstatite chondrites

We studied a thin section of Lewis Cliff (LEW) 87223, an unusual EL3-related, enstatite chondrite (EC) that has primary and secondary features not observed in other ECs. We studied its metal-rich nodules, possible shock features, and chondrules, eight of which are Al-rich chondrules (ARCs). LEW 87223 has petrologic and compositional features similar to EL3s. Enstatite is the dominant mineral; chondrule boundaries are well defined; Si content of metal (0.5–0.6 wt%) is consistent with typical EL3; it has Cr-bearing troilite, oldhamite, and alabandite; and its O-isotopic composition is similar to other ECs. However, metal abundance in LEW 87223 (~13 vol%) is slightly higher than in other EL3s and its metal nodules are texturally and mineralogically different from other ECs. Both high and low Ni metals are present, and its alabandite has higher Fe (27.8 wt% Fe) than in other EL3s. Silicates appear darkened in plane polarized light, largely due to reduction of Fe from silicate. A remarkable feature of LEW 87223 is the high abundance of ARCs, which contain Ca-rich plagioclase and varying amounts of Na-rich plagioclase along chondrule edges and as veins. This suggests Na metasomatism and the possibility of hydrothermal fluids, potentially related to an impact event. LEW 87223 expands the range of known EC material. It shows that ECs are more diverse and record a wider range of parent body processes than previously known. LEW 87223 is an anomalous EL3, potentially the first member of a new EC group should similar samples be discovered.     

Impact melting of the largest known enstatite meteorite: Al Haggounia 001, a fossil EL chondrite

Al Haggounia 001 and paired specimens (including Northwest Africa [NWA] 2828 and 7401) are part of a vesicular, incompletely melted, EL chondrite impact melt rock with a mass of ~3 metric tons. The meteorite exhibits numerous shock effects including (1) development of undulose to weak mosaic extinction in low‐Ca pyroxene; (2) dispersion of metal‐sulfide blebs within silicates causing “darkening”; (3) incomplete impact melting wherein some relict chondrules survived; (4) vaporization of troilite, resulting in S₂ bubbles that infused the melt; (5) formation of immiscible silicate and metal‐sulfide melts; (6) shock‐induced transportation of the metal‐sulfide melt to distances >10 cm; (7) partial resorption of relict chondrules and coarse silicate grains by the surrounding silicate melt; (8) crystallization of enstatite in the matrix and as overgrowths on relict silicate grains and relict chondrules; (9) crystallization of plagioclase from the melt; and (10) quenching of the vesicular silicate melt. The vesicular samples lost almost all of their metal during the shock event and were less susceptible to terrestrial weathering; in contrast, the samples in which the metal melt accumulated became severely weathered. Literature data indicate the meteorite fell ~23,000 yr ago; numerous secondary phases formed during weathering. Both impact melting and weathering altered the meteorite's bulk chemical composition: e.g., impact melting and loss of a metal‐sulfide melt from NWA 2828 is responsible for bulk depletions in common siderophile elements and in Mn (from alabandite); weathering of oldhamite caused depletions in many rare earth elements; the growth of secondary phases caused enrichments in alkalis, Ga, As, Se, and Au.     

An olivine-microchondrule-bearing clast in the Krymka meteorite

Abstract— A small (150 × 200-μm-size) clast consisting of 20 vol.% olivine microchondrules (with barred and granular textures) and 80 vol.% recrystallized silicate matrix material occurs in Krymka (LL3.1). This is the fourth microchondrule-bearing clast to be described. The chondrules are zoned in FeO with concentrations increasing toward the surface. The clast most closely resembles a previously described radial-pyroxene-microchondrule-bearing clast in Piancaldoli (LL3.4).     

Fractionated sulfur isotopes in sulfides of the Kaidun meteorite

Abstract— The Kaidun meteorite contains carbonaceous chondrite (CM1) clasts that have been highly altered by reactions with hydrothermal fluids. Pyrrhotite in these clasts occurs as unusual needles wrapped by sheaths of phyllosilicate, and pentlandite forms veins that crosscut aggregates of phyllosilicate and garnet but not pyrrhotite. The isotopic compositions of S (δ³⁴S_CDT) in individual sulfide grains, measured by ion micro-probe, are fractionated compared to troilite in ordinary chondrites. The S in Kaidun sulfides is isotopically light (as much as ?4.2% for pyrrhotite and ?5.7%0 for pentlandite), unlike sulfides in other carbonaceous chondrites, which are enriched in ³⁴S. The unusual S-isotopic composition of these texturally unique sulfides supports the hypothesis that Kaidun CM1 clasts were pervasively altered under extreme thermal conditions, possibly by fluids that had lost isotopically heavy SO₂.     

The Kaidun meteorite: Clasts of alkaline‐rich fractionated materials

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.     

Fayalitic olivine in CV3 chondrite matrix and dark inclusions: A nebular origin

Abstract— Fayalitic olivine (Fa₃₂) is the major component of the matrices and dark inclusions of CV3 and other unequilibrated chondrites. It occurs most commonly as rims, veins and halos in and around chondrule silicates in the Allende-type (CV3_OXA) chondrites and, to a much lesser extent, in the reduced (CV3R) and Bali-type (CV3OXB) chondrites. The olivines have distinctive platy, tabular and lath- or irregular-shaped crystals, with the ratio of the two types varying widely. In CV3_OXB chondrites, matrix fayalitic olivines range up to Fag_99.9; whereas, in the other CV3 chondrites, the range is much smaller. The platy and tabular anisotropic forms of the fayalitic olivines strongly suggest growth from a vapor, and the nature of the occurrences suggests that CV3 matrices are unequilibrated mixtures of nebular materials. We argue that the parent body hydration/dehydration model has numerous inconsistencies that make this hypothesis highly unlikely. These include: (1) There is no direct evidence linking fayalitic olivine to precursor phyllosilicates. (2) Dehydration of phyllosilicates cannot explain the wide range of morphologies of the fayalitic olivines. (3) Fayalitic olivine clearly predates the formation of the hydrous phases in CV3 chondrites and is one of the phases that breaks down to form phyllosilicates (Keller et al., 1994). (4) The unequilibrated nature of the matrix, including fine-scale zoning in 10 μm sized fayalitic olivine crystals, would not survive the parent body metamorphism required in the dehydration model. (5) A dark inclusion in the Ningqiang chondrite contains fayalitic olivine rimmed by glassy and microcrystalline material (Zolensky et al., 1997), which probably formed by radiation damage. This indicates that the fayalitic olivine was exposed to solar radiation in a nebular setting. (6) Some Allende chondrules contain unaltered primary, anhydrous glassy mesostasis in contact with the host matrix (e.g., Ikeda and Kimura, 1995). Chondrule mesostases would not have survived parent body hydration without becoming hydrated and would probably not survive the metamorphic heating required in the dehydration scenario. (7) Single platy and barrel-shaped crystals of fayalitic olivine are present in accretionary rims in calcium-aluminum-rich inclusions (CAIs) (MacPherson and Davis, 1997), which developed in the nebula. (8) Matrix lumps completely encased in chondrules in ordinary chondrites contain mainly fayalitic olivine (Scott et al., 1984), which indicates a nebular origin. (9) Oxygen isotopic compositions of Allende matrix and dark inclusions strongly indicate little or no hydration for Allende and its components (Clayton, 1997). We favor a nebular vaporization/recondensation model in which vaporization of chondritic dust produced a fayalite-rich vapor, followed by formation of the fayalitic olivine by direct recondensation from the vapor, epitactic growth on surfaces of existing forsterite and enstatite in chondrules, and replacement of existing forsterite and enstatite by gas-solid exchange.     

The Wold Cottage meteorite: Not just any ordinary chondrite

Abstract— The Wold Cottage meteorite (fell, 1795), as is well known, played an important part in meteorites being accepted as stones from the sky. In most cases, the very select group of people who have been privileged to witness any meteorite fall, let alone one as important as Wold Cottage, enjoy a moment's fame but then disappear into obscurity. In this respect, Wold Cottage is very different; Edward Topham, the man who reported the fall and who became the meteorite's publicist, was already very well known for many other reasons. This fact contributed substantially to the evidence provided by his workmen being accepted, following two public exhibitions of the meteorite, the second after sworn testimonies were obtained. Here we explore Topham's background in order to reveal his character, particularly the value he placed on truth. When he passed the meteorite over to a public museum, he did so in the belief that he was acting for the benefit of posterity. At a time when the idea of meteorites being extraterrestrial was still controversial, the Wold Cottage stone vitally prompted the observation that specimens from different parts of the globe closely resembled each other, thus stimulating the crucial chemical analyses which verified that they were indeed related. During its first twenty years on Earth, the Wold Cottage meteorite was a prized specimen, a public attraction and sought after for scientific teaching purposes. In researching Wold Cottage, we have been able to discover information about many of the personalities who were involved in providing and studying the first few meteorites to become available for scientific research. The Wold Cottage story gives an interesting perspective on the cultural scene at the end of the eighteenth and beginning of the nineteenth centuries when there was no clear distinction between the arts and sciences, and meteoritics was the prerogative of often rather flamboyant gentlemen.     

The Juancheng chondrite: A new meteorite fall from China

Abstract— A new meteorite, the Juancheng chondrite, fell recently in Juancheng County, Shandong Province, China. It is classified as an H5 (S2) chondrite on the basis of the compositions of olivine (Fa 19.2, σ_Fa 0.46), low-Ca pyroxene (Fs 16.9, σ_Fs 0.4) and Co contents of kamacite (0.36–0.47 wt%). Plagioclase is compositionally heterogeneous.     

The Loxton meteorite: A new olivine-bronzite chondrite from South Australia

Abstract— The Loxton meteorite is a single stone of 22 g found in South Australia in 1968. It has been classified as an L5 chondrite, shock facies ‘a,’ and contains olivine (Fa₂₄), orthopyroxene (Fs_21–22), clinopyroxene (Wo_44.7En_45.9Fs_9.4), nickel-iron, troilite, chromite and chlorapatite.     

The Galkiv meteorite: A new H4 chondrite from Ukraine

Abstract— The Galkiv chondrite is a single 5 kg stone that fell in the Chernigov region of Ukraine on 1995 January 12. The composition of olivines in the meteorite indicate that Galkiv belongs to the H group of ordinary chondrites. Although the heterogeneity of olivine corresponds to a petrologic type 5 and the heterogeneity of low-Ca pyroxene suggests the chondrite is type 3, clearly defined chondrule boundaries, the presence of clinopyroxene, cryptocrystalline glass and rare grains of feldspatic plagioclase, structural evidences of shock metamorphism and very low level of terrestrial weathering allow us to classify the meteorite as an H4 chondrite of shock stage S3 and weathering grade WO.     

The Hashima,Japan H4 chondrite: A newly reported meteorite

Abstract We report a new chondrite that fell in Hashima City in central Japan sometime during the period 1868–1912. The chondrite weighs 1110.64 g and exhibits distinct chondritic structure. Chondrules occupy 24 vol% of the stone and consist of olivine (average Fa_17,8), low-Ca pyroxene (average Fs_15,8 Wo_0.9), devitrified glass and lesser amounts of oligoclase (ca. Ab₈₀Or₄), kamacite, taenite, troilite and chromian spinel. Matrix occupying 76 vol% of the stone consists of olivine, low-Ca pyroxene, kamacite, taenite, troilite, cryptocrystalline minerals and lesser amounts of chromian spinel and chlorapatite. Matrix minerals have the same compositions as those in chondrules. Mineral chemistry, bulk chemistry and magnetic properties indicate that Hashima is an H-group chondrite. Well-defined chondrules, scarcely recrystallized oligoclase and relatively small variations of olivine and low-Ca pyroxene compositions indicate that Hashima is of petrologic type 4.     

The Cali meteorite fall: A new H/L ordinary chondrite

Abstract— The fall of the Cali meteorite took place on 6 July 2007 at 16 h 32 ± 1 min local time (21 h 32 ± 1 min UTC). A daylight fireball was witnessed by hundreds of people in the Cauca Valley in Colombia from which 10 meteorite samples with a total mass of 478 g were recovered near 3°24.3′N, 76°30.6′W. The fireball trajectory and radiant have been reconstructed with moderate accuracy. From the computed radiant and from considering various plausible velocities, we obtained a range of orbital solutions that suggest that the Cali progenitor meteoroid probably originated in the main asteroid belt. Based on petrography, mineral chemistry, magnetic susceptibility, thermoluminescence, and bulk chemistry, the Cali meteorite is classified as an H/L4 ordinary chondrite breccia.     

Northwest Africa 2526: A partial melt residue of enstatite chondrite parentage

Abstract— NWA 2526 is a coarse‐grained, achondritic rock dominated by equigranular grains of polysynthetically twinned enstatite (?85 vol%) with frequent 120° triple junctions and ?10–15 vol% of kamacite + terrestrial weathering products. All other phases including troilite, daubreelite, schreibersite, and silica‐normative melt areas make up 相似文献   

The silicate inclusions of the Ocotillo IAB iron meteorite

Abstract— The Ocotillo IAB iron meteorite contains small silicate inclusions consisting of olivine, low-Ca pyroxene, chromian diopside, plagioclase, magnesiochromite, apatite, troilite and metal. The ferromagnesian silicates have a small range of Fe/(Fe + Mg) ratios that are not due to zoning. These phases appear to be not well equilibrated. The FeO content of magnesiochromite is lower than values normally seen in silicate assemblages in IAB iron meteorites. The minerals in Ocotillo are generally like silicate assemblages in other IAB meteorites, covering similar composition ranges and exhibiting a metamorphic (granoblastic) texture. An estimate was made of the bulk composition of Ocotillo silicate inclusions. The bulk composition is close to that of ordinary chondrites with the exception of a deficiency in CaO that might be due to a sampling problem associated with the method used to estimate the bulk composition.     

The Hadley Rille enstatite chondrite and its agglutinate-like rim: Impact melting during accretion to the Moon

Abstract— Hadley Rille is a millimeter-size EH chondrite containing euhedral and acicular enstatite grains, kamacite globules and preferentially aligned silicate aggregates separated by elongated kamacite-rich patches. The Hadley Rille chondrite was significantly impact melted when it accreted to the lunar regolith at relative velocities of ～>3 km s^?1; ～65–75% of the chondrules present initially were melted. During the impact, portions of the local regolith were melted and an agglutinate-like rim formed around the chondritic projectile; the rim consists of flow-banded vesicular glass, blebs of troilite and low-Ni metallic Fe, rock fragments, glass(?) shards, and mineral grains. The mineral grains include enstatite (which is otherwise absent from the Moon and must have been derived from the projectile) and poorly characterized, micrometer-size phases enriched in light rare-earth-elements (LREE), which probably formed during the impact. Several of the rock fragments contain <33 mg/g Cl, which was probably derived through impact-induced volatilization of Cl from chondrule mesostases in the EH projectile.     

Origin of a metamorphosed lithic clast in CM chondrite Grove Mountains 021536

Abstract– A metamorphosed lithic clast was discovered in the CM chondrite Grove Mountains 021536, which was collected in the Antarctica by the Chinese Antarctic Research Exploration team. The lithic clast is composed mainly of Fe‐rich olivine (Fo₆₂) with minor diopside (Fs_9.7–11.1Wo_48.3–51.6), plagioclase (An_43–46.5), nepheline, merrillite, Al‐rich chromite (21.8 wt% Al₂O₃; 4.43 wt% TiO₂), and pentlandite. Δ¹⁷O values of olivine in the lithic clast vary from ?3.9‰ to ?0.8‰. Mineral compositions and oxygen isotopic compositions of olivine suggest that the lithic clast has an exotic source different from the CM chondrite parent body. The clast could be derived from strong thermal metamorphism of pre‐existing chondrule that has experienced low‐temperature anhydrous alteration. The lithic clast is similar in mineral assemblage and chemistry to a few clasts observed in oxidized CV3 chondrites (Mokoia and Yamato‐86009) and might have been derived from the interior of the primitive CV asteroid. The apparent lack of hydration in the lithic clast indicates that the clast accreted into the CM chondrite after hydration of the CM components.     

FeO‐rich silicates in the Sahara 97159 (EH3) enstatite chondrite: Mineralogy,oxygen isotopic compositions,and origin

Abstract— We report the mineralogy and oxygen isotopic compositions of FeO‐rich silicates in the Sahara 97159 EH3 chondrite. This component is referred to as FeO‐rich because it contains substantially more FeO than the characteristic FeO‐poor silicates in the highly reduced enstatite meteorites. These FeO‐rich silicates are mostly low‐Ca pyroxene (Fs5–35) and their compositions suggest an origin under more oxidizing conditions, like those for the ordinary chondrites. However, the mafic silicates in ordinary and carbonaceous chondrites are dominantly olivine, and the FeO‐rich silicates in the E chondrites are less commonly olivine. The oxygen isotopic compositions of the FeO‐rich silicates are indistinguishable from those of FeO‐poor silicates in Sahara 97159. These observations suggest that both the FeO‐rich silicates and the FeO‐poor silicates in EH chondrites formed from the same oxygen reservoir where redox conditions varied widely.     

Mineralogy and chemistry of Rumuruti: The first meteorite fall of the new R chondrite group

Abstract— The Rumuruti meteorite shower fell in Rumuruti, Kenya, on 1934 January 28 at 10:43 p.m. Rumuruti is an olivine-rich chondritic breccia with light-dark structure. Based on the coexistence of highly recrystallized fragments and unequilibrated components, Rumuruti is classified as a type 3–6 chondrite breccia. The most abundant phase of Rumuruti is olivine (mostly Fa_～39) with about 70 vol%. Feldspar (～14 vol%; mainly plagioclase), Ca-pyroxene (5 vol%), pyrrhotite (4.4 vol%), and pentlandite (3.6 vol%) are major constituents. All other phases have abundances below 1 vol%, including low-Ca pyroxene, chrome spinels, phosphates (chlorapatite and whitlockite), chalcopyrite, ilmenite, tridymite, Ni-rich and Ge-containing metals, kamacite, and various particles enriched in noble metals like Pt, Ir, arid Au. The chemical composition of Rumuruti is chondritic. The depletion in refractory elements (Sc, REE, etc.) and the comparatively high Mn, Na, and K contents are characteristic of ordinary chondrites and distinguish Rumuruti from carbonaceous chondrites. However, S, Se, and Zn contents in Rumuruti are significantly above the level expected for ordinary chondrites. The oxygen isotope composition of Rumuruti is high in δ¹⁷O (5.52 ‰) and δ¹⁸O (5.07 ‰). Previously, a small number of chondritic meteorites with strong similarities to Rumuruti were described. They were called Carlisle Lakes-type chondrites and they comprise: Carlisle Lakes, ALH85151, Y-75302, Y-793575, Y-82002, Acfer 217, PCA91002, and PCA91241, as well as clasts in the Weatherford chondrite. All these meteorites are finds from hot and cold deserts having experienced various degrees of weathering. With Rumuruti, the first meteorite fall has been recognized that preserves the primary mineralogical and chemical characteristics of a new group of meteorites. Comparing all chondrites, the characteristic features can be summarized as follows: (a) basically chondritic chemistry with ordinary chondrite element patterns of refractory and moderately volatile lithophiles but higher abundances of S, Se, and Zn; (b) high degree of oxidation (37–41 mol% Fa in olivine, only traces of Fe, Ni-metals, occurrence of chalcopyrite); (c) exceptionally high Δ¹⁷O values of about 2.7 for bulk samples; (d) high modal abundance of olivine (～70 vol%); (e) Ti-Fe³⁺?rich chromite (～5.5 wt% TiO₂); (f) occurrence of various noble metal-rich particles; (g) abundant chondritic breccias consisting of equilibrated clasts and unequilibrated lithologies. With Rumuruti, nine meteorite samples exist that are chemically and mineralogically very similar. These meteorites are attributed to at least eight different fall events. It is proposed in this paper to call this group R chondrites (rumurutiites) after the first and only fall among these meteorites. These meteorites have a close relationship to ordinary chondrites. However, they are more oxidized than any of the existing groups of ordinary chondrites. Small, but significant differences in chemical composition and in oxygen isotopes between R chondrites and ordinary chondrites exclude formation of R chondrites from ordinary chondrites by oxidation. This implies a separate, independent R chondrite parent body.