Chondrule types include porphyritic (FeO-poor and FeO-rich), barred olivine, radial pyroxene, granular, and cryptocrystalline. Chondrules in unequilibrated OC tend to have unfractionated refractory lithophile abundances; metallic components include one enriched in refractory siderophiles and one in common and volatile siderophiles. Although most chondrules are a few hundred µm in diameter, microchondrules (0.8-40 µm) and macrochondrules (0.5–5 cm) also occur. Compound chondrules include enveloping, sibling, and adhering varieties. Some chondrules have fine-grained rims, others igneous rims. Relict grains survived the most recent chondrule melting. Calcium–aluminum-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) are very rare. Matrix material occurs mainly as chondrule rims and isolated lumps. Carbon-rich aggregates and clasts contain poorly graphitized C, amorphous C, metallic Fe-Ni, and minor chromite. A few H chondrites contain halite. Opaque assemblages include metallic Fe-Ni, sulfide, and oxides. Some shocked OC contain metallic Cu. Large metal nodules formed by impact-induced vaporization and fractional condensation. Many shocked OC exhibit silicate darkening, and many are breccias with a variety of clasts. Some OC are regolith breccias enriched in solar-wind-implanted noble gases.

OC parent bodies accreted from a mix of chondrules, chondrule fragments, grains of metallic Fe-Ni and sulfide, porous aggregates of fine-grained dust, and rare CAIs, AOAs, and tiny presolar grains. After accretion, the OC asteroids underwent thermal metamorphism, mainly due to the decay of 26Al. They initially developed onion-shell structures but suffered disruption and reassembly while still hot. Subsequent collisions produced a variety of breccias on each body. The L parent asteroid was destroyed by a catastrophic collision ~470 Ma ago.

Compositions and classification of chondritic and differentiated meteories and of interplanetary dust particles