Surface energetics of ground calcium carbonates (GCC), with or without stearic acid treatment, were determined by Inverse Gas Chromatography (IGC). The surface energy data were utilized as a predictive tool to explain the optimum coating level often needed on calcium carbonate minerals to obtain the desirable mechanical strength in filled polypropylene composites. The dispersive components of the surface energies for the uncoated carbonates were also correlated with the corresponding impact resistance data. The surface with the highest energy was found to be the least resistant while the least energetic mineral, on a comparative scale, was the most resistant to impact. It is suggested that understanding the surface energetics of finely-divided solids may be a key for the development of future mineral-filled polymer composites.