The Phosphate Mineralogy of Meteorites

Abstract

Nine phosphate minerals are found in meteorites: whitlockite, Ca3(PO4)2; chlorapatite, Ca5(PO4)3Cl; hydroxyapatite, Ca5(PO4)3OH; sarcopside, (Fe, Mn)3(PO4)2; graftonite, (Fe, Mn)3 (PO4)2; farringtonite, Mg3(PO4)2; stanfieldite, Ca4(Mg, Fe)5(PO4)6; brianite, Na2MgCa(PO4)2; and panethite, Na2Mg2(PO4)2. The last four have been found only in meteorites.Ordinary chondrites contain whitlockite and chlorapatite but no other phosphates. This fact probably results from the uniform composition of these chondrites. The other phosphates are found in more differentiated classes of meteorites, where their presence is related to the chemical environment.Whitlockite is the predominant phosphate mineral in meteorites. Small variations in its composition can be correlated with other compositional features that vary from one class of meteorites to another. Chlorapatite is found in meteorites to the exclusion of fluorapatite, which is the common apatite found in igneous rocks.If phosphate minerals are in equilibrium with associated schreibersite, a relative degree of oxidation can be calculated for those meteorites that contain a particular phosphide-phosphate pair. Trace amounts of schreibersite found in some chondrites may or may not indicate equilibrium with associated phosphate minerals.