Apatite
Apatite is a calcium phosphate that can contain water, fluorine and chlorine, making it a tracer of volatiles in meteorites.
Apatite is a calcium phosphate mineral that also holds fluorine, chlorine or hydroxyl, a pair of hydrogen and oxygen atoms. It is the same mineral family that makes up tooth enamel and bone.
In meteorites, apatite usually forms tiny grains alongside merrillite. It is found in ordinary chondrites, eucrites, angrites and lunar and Martian rocks. Because it can lock up water, chlorine and fluorine as it crystallises, apatite is one of the best tools for estimating how much water and other volatile substances were present in magmas on the Moon, Mars and Vesta. Measurements of hydrogen isotopes in lunar apatite helped revive the idea that the Moon is not completely dry.
Apatite also contains uranium, so it can be dated using uranium–lead methods. In chondrites, the balance of chlorine and fluorine in apatite records fluids that moved through the parent body during heating.
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