Type I and type II chondrules
Type I chondrules are poor in iron oxide and often contain metal; type II chondrules are rich in iron oxide.
Chondrules are divided into two chemical kinds. Type I chondrules contain olivine and pyroxene with very little iron oxide, usually under about 10 per cent fayalite, and often contain beads of iron-nickel metal. Type II chondrules have more iron in their silicates, so their olivine is more iron-rich, and they usually have little metal.
The difference reflects the oxygen level when each chondrule formed. Type I chondrules formed in more reducing conditions, where iron stayed as metal; type II formed where iron was oxidised and entered the silicates. Each type is further labelled by texture, so a chondrule might be described as type IA, rich in olivine, or type IIAB, with both olivine and pyroxene.
Carbonaceous chondrites are dominated by type I chondrules, while ordinary chondrites contain a large share of type II. The two types and their proportions offer clues about where in the disc each chondrite group gathered its ingredients.
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