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Chondrules in the chondrite classification Grassland. A millimeter scale is shown. Chondrules in the Carbonaceous Chondrite NWA 13887. A chondrule (from Ancient Greek χόνδρος chondros, grain) is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids.
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Chondrules, metal grains, and other components likely formed in the solar nebula. These accreted together to form parent asteroids. These accreted together to form parent asteroids. Some of these bodies subsequently melted, forming metallic cores and olivine -rich mantles ; others were aqueously altered. [ 35 ]
Aqueous alteration promotes a composition of hydrous phyllosilicates, magnetite, and olivine crystals occurring in a black matrix, and a possible lack of chondrules. It is thought they have not been heated above 50 °C (122 °F), indicating that they condensed in the cooler outer portion of the solar nebula.
Many CM chondrules are surrounded by either rims of accessory minerals, or haloes of water-altered chondrule material. [29] [30] The chondrules of CM chondrites, though fewer, are larger than in COs. While CM chondrules are smaller than average in diameter (~300 micrometer), CO chondrules are exceptionally small (~170 um).
The 1 in C1 stands for the type 1 meteorites in the older classification scheme of Van Schmus-Wood, [4] still used for petrography. Petrographic type-1 meteorites, by definition, have no fully-visible chondrules .
LL chondrites contain the largest chondrules of the ordinary chondrite groups, averaging around 1 millimetre (0.039 in) diameter.. The LL group includes many of the most primitive ordinary chondrites, including the well-studied Semarkona (type 3.0) chondrite.