Crystal chemistry of natural aluminium phosphates

A crystal-chemistry survey on natural aluminium phosphates, carried out by combining EMPA micronalysis, single-crystal X-ray diffraction and FTIR spectroscopy, was performed starting from our studies on whiteite CaFeMgAl2(PO4)4(OH)2∙8H2O, augelite Al2(PO4)(OH)3, wardite NaAl3(PO4)2(OH)4∙2H2O, lazulite MgAl2(PO4)2(OH)2 and wavellite Al3(PO4)2(OH,F)3·5H2O, and extending the investigation to the most common Al phosphates phases. Main crystallographic features (bonds, angles, interactions) were examined according to the results of structural refinements, and the presence of networks of O-H…O hydrogen bonds with in the structures, based on the Libowitzky (1999) relationship, for the range of D-H...A bond systems in the structure, in order to compare results of OH frequencies from FTIR spectra with those observed by X-ray refinement.