The most primitive of the three main classes of chondrite meteorite, with compositions that most closely resemble that of the Sun, except for the most volatile elements. They probably date from early in the formation of the Solar System. Carbonaceous chondrites are divided into eight subgroups on the basis of composition: CI, CM, CO, CV, CR, CB, CH, and CK, plus a number of ungrouped meteorites. The CI subgroup are the most primitive, having the lowest density, the highest content of volatiles and carbon, and compositions most closely resembling that of the Sun; they contain abundant phyllosilicates but no chondrules. Type CM contain abundant phyllosilicates and less than 15% chondrules with average diameter around 0.3 mm. Type CO contain 35–40% chondrules, with typical diameters of 0.2–0.3 mm. Type CV also contain 35–45% chondrules, but with average diameters of about 1 mm; these can be further divided into three groups based on their degree of oxidation. The CR chondrites contain abundant phyllosilicates, around 5% metallic iron, and 50% chondrules, with typical diameters of 0.7 mm. The CB subgroup, often called bencubbinites, contain >50% metallic iron and millimetre- to centimetre-sized chondrules. The CH chondrites contain around 20% metallic iron and tiny chondrules of 0.02 mm diameter. Together the CR, CB, and CH chondrites are sometimes referred to as the CR clan, as they share similarities in mineralogy and composition. The CK chondrites contain millimetre-sized chondrules and were thermally metamorphosed. Each subgroup may be further divided into various subtypes on the basis of their texture and mineralogy (e.g. CI1, CM2, CO3, and CV3). All groups contain complex organic molecules.