Apatite is a group of minerals, usually referring to: hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl-ions, respectively, in the crystal lattice. The formula of the admixture of the three most common species is Ca5(PO4)3(OH, F, Cl).
Apatite is one of very few minerals which are produced and used by biological systems. Hydroxyapatite is the major component of tooth enamel, and a large component of bone material. Fluorapatite is slightly stronger than hydroxyapatite; thus, fluoridated water, which will allow exchange in the teeth of hydroxyl ions for fluoride ions, slightly strengthens the teeth.
Fission tracks in apatite are commonly used to estimate the thermal history of sediments in sedimentary basins.
Phosphorite is the name given to impure, massive apatite.
The crystals occur principally in vugs in altered beryl crystals and are associated with a replacement assemblage of bertrandite, cookeite, and Fe/Mn oxide pseudomorphs after siderite/rhodochrosite.
Fluorapatites from the Emmons pegmatite may show very complex and beautiful zoning patterns with oscillatory zones, chaotic zoning, as well as areas exhibiting partial dissolution with later overgrowth.
All fluorapatites analyzed are close to end-member fluorapatite, Ca5(PO4)3F with a wide range of Mn and Sr impurities.
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