Dolomite
Dolomite is a calcium-magnesium carbonate formed by water inside CI and some CM chondrite parent bodies.
Dolomite is a carbonate mineral containing both calcium and magnesium, CaMg(CO3)2. On Earth it forms extensive rocks, including the Dolomite mountains of Italy.
In meteorites, dolomite occurs as small grains in CI chondrites and in some heavily altered CM chondrites, as well as in samples from the asteroid Ryugu. It formed from carbonated water circulating inside the parent asteroid. Its presence alongside calcite and breunnerite, an iron-magnesium carbonate, shows that the fluids changed chemistry over time.
Dolomite grains are useful clocks. They contain manganese, so the decay of the extinct isotope manganese-53 to chromium-53 can be measured, giving ages for the watery episode. Results suggest liquid water was active on carbonaceous asteroids within the first few million years of Solar System history, a striking sign of how quickly these bodies warmed up from radioactive heat.
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