Compounds of composition Pb-5(PO4)(3)FxCl1-x (0 <= x <= 1), which are synthetic analogues of minerals pyromorphite, flourapatite, and endlichite, were synthesized for the first time by high-temperature solid phase reactions. X-ray diffraction and IR spectroscopy were used to determine the structure of the compounds and revealed complete miscibility in the solid phase of the Pb-5(PO4)(3)F-Pb-5(PO4)(3)Cl binary system. Adiabatic reaction calorimetry was used to measure standard enthalpies of mixing and formation and show that the regular solutions model is applicable to the Pb-5(PO4)(3)F-Pb-5(PO4)(3)Cl system. Differential thermal analysis in tandem with high-temperature X-ray diffraction were used to study the phase diagram and characterize phase transitions. (C) 2010 Elsevier B.V. All rights reserved.