Natural Magnesium Hydrous Orthophosphates Bobierrite and Kovdorskite: FTIR, Raman, Thermal, and Thermochemical Study

— A physicochemical study of natural hydrous magnesium orthophosphates bobierrite Mg 3 [PO 4 ] 2 · 8H 2 O and kovdorskite Mg 2 [PO 4 ](OH) · 3H 2 O from the Kovdor carbonatite massif, Kola Peninsula, Russia, was carried out using X-ray diffraction, infrared spectroscopy, Raman spectroscopy, and thermal analysis. The enthalpies of dehydration of the minerals were measured using a NETZSCH DSC 204 F1 differential scanning calorimeter, the enthalpies of formation from the elements for bobierrite (–6167 ± 16 kJ/mol) and kovdorskite (–3251 ± 10 kJ/mol) were determined by high-temperature melt solution calorimetry on a Setaram high-temperature heat-flux Tian–Calvet microcalorimeter. The values of their standard entropies and Gibbs energies of formation are estimated.