The Crystal Structure of Apatite, Ca5(PO4)3(F,OH,Cl)

Abstract

As illustrated by the broad range of topics presented in this volume, the mineral apatite, Ca5(PO4)3(F,OH,Cl), is of importance in a greater variety of fields than virtually any other mineral. It is of particular significance in Earth science, life science, and material science; the foundation of this significance is the apatite atomic arrangement. Apatite is the most abundant naturally occurring phosphate on Earth. Consequently, it is the major source of phosphorous, both as an ore and the base of the global phosphorous cycle. As the major ore mineral of phosphorous, apatite is critical for the production of huge quantities of fertilizers, detergents and phosphoric acid; the extracted phosphorous is also used in many other applications such as phosphors, rust removers, motor fuels, and insecticides to name but a few (McConnell 1973). The global biogeochemical cycling of phosphorous starts by its release from apatite at the Earth’s surface and ultimately leads to the formation of other geological apatites through sedimentary processes or tectonic recycling. Along the way, however, it is an essential element to all life on Earth (Filippelli, this volume). The structure and chemistry of apatite allow for numerous substitutions, including a multitude of metal cations (i.e., K, Na, Mn, Ni, Cu, Co, Zn, Sr, Ba, Pb, Cd, Sb, Y, REEs, U) that substitute for Ca in the structure, and anionic complexes (i.e., AsO43−, SO42−, CO32−, SiO44−, etc.) that replace PO43− (Pan and Fleet, this volume). Indeed, apatite incorporates half the periodic chart in its atomic arrangement. These substitutions are usually in trace concentrations, but large concentrations and even complete solid solutions exist for certain substituents. This complex and variable chemistry has great implications, and is utilized in all areas …