A colloidal dispersion of calcium thiophosphate in hydrocarbon medium was synthesized by reacting calcium oxide with tetraphosphorus decasulfide and water in the presence of a surfactant under specific conditions. The resulting product can be defined as a distribution of inorganic cores surrounded by a surfactant layer in a reverse-micelle-type association. The chemical composition was determined by P-31 NMR, dialysis, and thermogravimetric analysis. The core particles were found to be a mixture of calcium thiophosphates, consisting mainly of mono- and dithiophosphates, with a small amount of phosphate. Shape, size distribution, and average core radius were investigated using transmission electron microscopy and small angle X-ray scattering. According to these techniques, the colloidal species can be defined as polydisperse spherical micelles with the radius of the mineral cores ranging from 10 to 80 Angstrom.