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CB chondrites occur in two types, both of which are similar to CH chondrites in that they are very depleted in volatile elements and rich in metal. CB a (subgroup a) chondrites are coarse grained, with large, often cm-sized chondrules and metal grains and almost no refractory inclusions. Chondrules have unusual textures compared to most other ...
Again, different kinds of chondrites contain different ranges of chondrule sizes: they are smallest in CH, CM, and CO chondrites (see meteorite classification), moderately large in CR, CV, L, LL, and R chondrites, and largest in some CB chondrites (see table). Other chondrite groups are intermediate between these.
"H" stands for "high metal" because CH chondrites may contain up to as much as 40% of metal. [16] That makes them one of the most metal-rich of any of the chondrite groups, second only to the CB chondrites and some ungrouped chondrites such as NWA 12273. The first meteorite discovered was ALH 85085. Chemically, these chondrites are closely ...
The CM group most resembles the CI and CO chondrites; a CM–CO is sometimes described. [7] [8] [9] All three groups contain clearly anomalous 50 Ti and 54 Cr isotopes. [10] [11] Though the C-chondrites are far rarer than ordinary chondrites, the CM group is "the most abundant type of" them.
Ordinary chondrite NWA 3189 sliced. Field of view c. 2.2 cm across. NWA 3189 has been classified as an LL3.2–3.4 ordinary chondrite ("LL" means very low total iron content; "3" refers to well-preserved chondrules – the rock has not been subjected to metamorphism intense enough to disrupt the chondritic texture).
The LL group includes many of the most primitive ordinary chondrites, including the well-studied Semarkona (type 3.0) chondrite. However, most LL chondrites have been thermally metamorphosed to petrologic types 5 and 6, meaning that their minerals are homogeneous in composition and chondrule borders are difficult to discern.
Nagy B, Claus G, Hennessy DJ (1962) Organic Particles Embedded in Minerals in Orgueil and Ivuna Carbonaceous Chondrites. Nature 193 (4821) p. 1129; Fitch FW, Anders E (1963) Organized Element - Possible Identification in Orgueil Meteorite. Science 140 (357) p. 1097
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