Chondrites and Their Components

Abstract-Carbonaceous chondrites are classified into several groups. However, some are ungrouped. We studied one such ungrouped chondrite, Y-82094, previously classified as a CO. In this chondrite, chondrules occupy 78 vol%, and the matrix is distinctly poor in abundance (11 vol%), compared with CO and other C chondrites. The average chondrule size is 0.33 mm, different from that in C chondrites. Although these features are similar to those in ordinary chondrites, Y-82094 contains 3 vol% Ca-Al-rich inclusions and 5% amoeboid olivine aggregates (AOAs). Also, the bulk composition resembles that of CO chondrites, except for the volatile elements, which are highly depleted. The oxygen isotopic composition of Y-82094 is within the range of CO and CV chondrites. Therefore, Y-82094 is an ungrouped C chondrite, not similar to any other C chondrite previously reported. Thin FeO-rich rims on AOA olivine and the mode of occurrence of Ni-rich metal in the chondrules indicate that Y-82094 is petrologic type 3.2. The extremely low abundance of type II chondrules and high abundance of Fe-Ni metal in the chondrules suggest reducing condition during chondrule formation. The depletion of volatile elements indicates that the components formed under high-temperature conditions, and accreted to the parent body of Y-82094. Our study suggests a wider range of formation conditions than currently recorded by the major C chondrite groups. Additionally, Y-82094 may represent a new, previously unsampled, asteroidal body.

Section: Classification Of Chemical Groupmentioning

confidence: 83%

Petrology and bulk chemistry of Yamato‐82094, a new type of carbonaceous chondrite

Kimura

Barrat

Weisberg

et al. 2014

“…The fragment LT1 from GCP, a forsterite-rich grain which contains modest amounts of anorthite and Al,Ti clinopyroxene + inclusions of Al-Mg-Fe-Cr spinel and Fe,Ni metal, is compositionally and mineralogically the least refractory of the nine comet fragments in this study. Mineralogically, LT1 resembles AOAs, which are observed in all carbonaceous and some ordinary chondrite groups (Scott and Krot 2005). In chondrites AOAs are principally composed of olivine, clinopyroxene, anorthite, and spinel AE minor kamacite, melilite, or perovskite (Komatsu et al 2001;Krot et al 2004b).…”

Section: Moderate Refractory Character Of Refractory Wild 2 and Gcp Fmentioning

confidence: 99%

Refractory materials in comet samples

Joswiak

Brownlee

Nguyen

et al. 2017

Transmission electron microscope examination of more than 250 fragments, >1 μm from comet Wild 2 and a giant cluster interplanetary dust particle (GCP) of probable cometary origin has revealed four new calcium‐aluminum‐rich inclusions (CAIs), an amoeboid olivine aggregate (AOA), and an additional AOA or Al‐rich chondrule (ARC) object. All of the CAIs have concentric mineral structures and are composed of spinel + anorthite cores surrounded by Al,Ti clinopyroxenes and are similar to two previous CAIs discovered in Wild 2. All of the cometary refractory objects are of moderate refractory character. The mineral assemblages, textures, and bulk compositions of the comet CAIs are similar to nodules in fine‐grained, spinel‐rich inclusions (FGIs) found in primitive chondrites and like the nodules may be nebular condensates that were altered via solid–gas reactions in the solar nebula. Oxygen isotopes collected on one Wild 2 CAI also match FGIs. The lack of the most refractory inclusions in the comet samples may reflect the higher abundances of small moderately refractory CAI nodules that were produced in the nebula and the small sample sizes collected. In the comet samples, approximately 2–3% of all fragments larger than 1 μm, by number, are CAIs and nearly 50% of all bulbous Stardust tracks contain at least one CAI. We estimate that ~0.5 volume % of Wild 2 material and ~1 volume % of GCP is in the form of CAIs. ARCs and AOAs account for <1% of the Wild 2 and GCP grains by number.

“…The apparent diameters of 192 measured chondrules range from 0.11 mm to 2.51 mm, with an average of 0.73 mm. The mean chondrule diameter in Jezersko is much larger than the mean diameter in H chondrites (Scott and Krot 2003;Weisberg et al 2006), indicating that the meteorite parent body was composed of larger and inhomogeneously distributed chondrules. Chondrules are mostly oval to spherical in shape.…”

Section: Petrographymentioning

confidence: 98%

Mineral and chemical composition of theJezersko meteorite—A new chondrite fromSlovenia

Miler

Ambrožič²,

Mirtič³

et al. 2014

The Jezersko meteorite is a newly confirmed stony meteorite found in 1992 in the Karavanke mountains, Slovenia. The meteorite is moderately weathered (W2), indicating short terrestrial residence time. Chondrules in partially recrystallized matrix are clearly discernible but often fragmented and have mean diameter of 0.73 mm. The meteorite consists of homogeneous olivine (Fa 19.4 ) and low-Ca pyroxenes (Fs 16.7 Wo 1.2 ), of which 34% are monoclinic, and minor plagioclase (Ab 83 An 11 Or 6 ) and Ca-pyroxene (Fs 6 Wo 45.8 ). Troilite, kamacite, zoned taenite, tetrataenite, chromite, and metallic copper comprise about 16.5 vol% of the meteorite. Phosphates are represented by merrillite and minor chlorapatite. Undulatory extinction in some olivine grains and other shock indicators suggests weak shock metamorphism between stages S2 and S3. The bulk chemical composition generally corresponds to the mean H chondrite composition. Low siderophile element contents indicate the oxidized character of the Jezersko parent body. The temperatures recorded by two-pyroxene, olivine-chromite, and olivine-orthopyroxene geothermometers are 854°C, 737-787°C, and 750°C, respectively. Mg concentration profiles across orthopyroxenes and clinopyroxenes indicate relatively fast cooling at temperatures above 700°C. A low cooling rate of 10°C Myr À1 was obtained from metallographic data. Considering physical, chemical, and mineralogical properties, meteorite Jezersko was classified as an H4 S2(3) ordinary chondrite.