The standard molar enthalpy of formation of thorium phosphate diphosphate,beta-Th-4(PO4)(4)P2O7(cr) has been determined using an isoperibol solution calorimeter, a differential scanning calorimeter and phase transition data of high temperature calorimeter. The enthalpy of precipitation of thorium phosphate-hydrogenphosphate hydrate, Th-2(PO4)(2)(HPO4).H2O(cr), was measured at 298.15 K using an isoperibol solution calorimeter. Heat capacities of alpha-Th-4(PO4)(4)P2O7(cr) and beta-Th4(PO4)(4)P2O7(cr) were measured using a Differential Scanning Calorimeter. Combining these experimental data, and other auxiliary data from the literature, thermo-chemical reaction scheme was devised to calculate the standard molar enthalpy of formation of beta-Th-4(PO4)(4)P2O7(cr) to be {-10565.5 +/- 13.6} kJ mol(-1). The thermodynamic functions for beta-Th-4(PO4)(4)P2O7(cr) have been computed using,Delta H-f(m)o(298.15 K), C-p,m(o)(T) and literature data. The Gibbs phase diagram and predominant area diagrams for Th-P-O system have been computed using the thermodynamic information of the various phase present in Th-P, P-O and ThO2-P2O5 systems. E-H-p(H) diagram of Th-P-H2O system has been computed to determine stability of Th4P6O23(cr) in ground water. (C) 2014 Elsevier B.V. All rights reserved.