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R Group (Rumurutiites)
Synonyms: rumurutiites, Carlisle-Lake-like chondrites
General: This group was formerly known as the Carlisle Lakes group, for a meteorite that was found in Australia in 1977. It is now officially named for the type specimen Rumuruti that fell in Kenya, Africa, in 1934. Rumuruti is the only witnessed fall of this group and just one small individual has been preserved in the collection of the Humboldt Museum Berlin, Germany, since 1938. It was thought to be an anomalous chondrite until it was reclassified in 1993 and the R group was formed.
Description: Most R chondrites belong to petrologic type 3 or are heavily brecciated members that show different lithologies from petrologic type 3 to 6. There are only a few R chondrites of higher petrologic types that are not brecciated, e.g. our own find Sahara 98248, an R4 from Northern Africa.
Mineralogy: The R chondrites are quite different from ordinary chondrites and they are the opposite of the E chondrites when it comes to mineralogy and their state of oxidation. The members of this group are highly oxidized, containing high amounts of iron-rich olivine. There is practically no free metal inside the R chondrites since most of the iron is either oxidized or found in the form of iron sulfides. The iron-rich olivines, along with the oxidized nature of the iron, give most R chondrites a typical red appearance.
Formation history: The meteorites of this group contain fewer chondrules than ordinary chondrites or enstatite chondrites, but they often contain xenolithic inclusions that indicate a regolith origin, representing samples of the surface of an asteroid. Another indicator for a regolith origin is the fact that most members of the R group contain high amounts of noble gases implanted into the rock by the solar wind.
Origin: The parent body of the R chondrites has yet to be found, but it surely must have been subjected to many impact events during its history resulting in the high degree of brecciation that most R group members exhibit.
Members: There are just about 30 R chondrites known if we exclude all probable pairings, especially from the hot deserts of Northwest Africa (NWA). Among the rumurutites the type specimen, Rumuruti, is the only witnessed fall. All others are mostly hot or cold desert finds. Our own finds include Sahara 98248, Sahara 99527, Sahara 99531, Sahara 99537, and Sahara 03013.