- © The Mineralogical Society Of America
Apatite, the most common phosphate mineral, is generally described by the formula Ca5(PO4)3(OH,F,Cl) or, more completely with regard to its usual description in P63/m symmetry, by the unit cell content [Ca4][Ca6][(PO4)6][OH,F,Cl]2. An earlier volume of the Reviews series (Kohn et al. 2002) has dealt with the mineralogy and crystallography of apatite sensu stricto (Hughes and Rakovan 2002) and the diverse compounds that adopt apatite or apatite-like structures (Pan and Fleet 2002; Huminicki and Hawthorne 2002). In addition, apatite compilations have appeared at regular intervals (Wychoff 1965; McConnell 1973; Nriagu and Moore 1984; Brown and Constantz 1994; Elliott 1994) as the breadth of apatite chemistry has expanded and the level of understanding of its importance with respect to the mineral, materials, environmental, and biological sciences increased. It is not therefore, the purpose of this chapter to restate these excellent reviews, but rather, to focus on microporosity in apatites, a feature which allows ion conduction and exchange, and that is proving to be an important consideration for fashioning synthetic analogues of these minerals in technologically advantageous ways.
The notion of apatite as an industrially significant microporous mineral is not new. In 1944, V. M. Goldschmidt who had studied apatite deposits in Scandinavia and at that time had found refuge from war-ravaged Europe at the Macaulay Institute of Soil Research, Aberdeen (Kauffman 1997; McIntyre 2004) persuaded C. A. Beevers to undertake a new refinement of fluorapatite. The results collected in the seminal paper of Beevers and McIntyre (1946), lead not only to the most accurate crystallographic data available at that time, but also provided the first overview of [Ca4][Ca6][(PO4)6][F] …