**4.9 Chalcogenide phosphate apatites**

The preparation and the structure of chalcogenide phosphate apatites of the composition Ca10(PO4)6S (calcium sulfoapatite), Sr10(PO4)6S (strontium sulfoapatite), Ba10(PO4)6S (barium sulfoapatite) and Ca10(PO4)6Se (calcium selenoapatite) was reported by HENNING et al [196]. These apatite phases are isostructural and crystallize in the trigonal space group*P*3 ¯.with the

<sup>52</sup> In human body radium behaves in a similar way as calcium. When ingested, it is readily adsorbed in bone where it may directly irradiate the bone and other tissues. This exposition may result in fatal disease as the tragic story of "*Radium girls*" working with luminous paint trade named: Undark (the mix of radium and zinc sulfide produced by U.S. Radium Corporation between 1917 and 1938) shows [136],[137].

chalcogenide ion positioned at (0 0 ½). The sulfoapatites show no ability to absorb H2S in the way oxyapatite absorbs H2O at elevated temperatures. This can be attributed to the position of sulfide ion and the way it influences the crystal structure around the vacant chalcogenide position at (000). Calcium sulfoapatites, Ca10(PO4)6S, can be successfully synthesized only using oxide starting materials with sulfur vapor under H2 atmosphere instead of toxic H2S gas [197].
