CK chondrite
CK chondrites are oxidised, thermally metamorphosed carbonaceous chondrites rich in magnetite.
CK chondrites are named after Karoonda, which fell in South Australia on 25 November 1930; around 42 kilograms were recovered. Unlike most carbonaceous chondrite groups, CKs span petrologic types 3 to 6, meaning many were heated substantially on their parent body. They are highly oxidised: olivine is relatively iron-rich (commonly around Fa29 to Fa33), metal is almost absent, and magnetite, often containing chromium, is abundant. Plagioclase and pentlandite are common.
Their silicates are frequently darkened by tiny inclusions of sulfide and magnetite introduced by shock, giving CKs their characteristically dark, sometimes black appearance despite being well recrystallised. Oxygen isotopes and CAI compositions overlap strongly with the CV chondrites, and many workers now argue that CVs and CKs form a continuous metamorphic sequence from one parent body, though this is still debated, partly because CKs seem to lack the large CV-like chondrule population in higher types.
Most CKs are finds from Antarctica and Northwest Africa, and Karoonda remains one of very few observed falls. Recognition relies on magnetite-rich, metal-poor mineralogy, darkened silicates, a chondritic texture with large chondrule ghosts, and bulk oxygen isotopes close to the CV field.
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