What is an R chondrite?
An R chondrite, or Rumuruti chondrite, is a rare, highly oxidised chondrite with abundant iron-rich olivine and almost no metal.
R chondrites, or Rumuruti chondrites, are named after the Rumuruti meteorite, which fell in Kenya in 1934. For a long time, it was the only witnessed fall of this kind, and it remains the only one. Many R chondrites have since been found in hot deserts and Antarctica.
Distinctive features. - They are highly oxidised: most of their iron is in silicate minerals rather than metal. They contain very little or no metallic iron. - Their olivine is iron-rich, with about 37 to 40 per cent fayalite, much higher than in ordinary chondrites. - They contain abundant sulfides, such as pyrrhotite and pentlandite. - Their oxygen isotopes are distinctive, plotting above the terrestrial fractionation line, with the highest Δ17O values of any chondrite group. - Many are regolith breccias, containing solar wind gases, and many contain clasts of different petrologic types.
Unusual examples. Some R chondrites contain amphibole and mica, water-bearing minerals rarely found in meteorites, suggesting that water or fluids were present on their parent body at high temperatures. LaPaz Icefield 04840 from Antarctica is an example.
Parent body. The R chondrite parent body is not identified. It is thought to have formed in a region richer in oxygen than the ordinary chondrite parent bodies.
Significance. R chondrites show the variety of conditions in the early Solar System, especially the range of oxidation states, and help scientists understand how chondrite parent bodies differed.