Using X ray photoelectron spectroscopy (XPS), we have determined that the composition of intergranular regions on olivine crystals of unaltered dunite and lherzolite xenoliths from flows in Hawaii, Australia, and Arizona are markedly different from the compositions of both the olivine and the host transporting lavas. The boundaries are without low-melting components, such as alkalis, but are rich in aluminium, silicon, magnesium and iron. While XPS spectra offer only semiquantitative analyses, the compositions of the intergranular regions appear to be such that they would remain unmelted at temperatures existing in the xenolith source regions. We infer that within their source regions, refractory dunite bodies, of which the Hawaiian dunites are samples, have solid mechanical contacts along the olivine grain boundaries. Furthermore, we feel that the compositions of surface films are established so as to minimize the surface free energy along intergranular faces as melt as gradually removed. This is consistent with the observed inability of the host lavas to penetrate these xenoliths during their absent to the surface. As such, the parent refractory material within the mantle appears to be effectively nonporous to the magma, and hence magma transport within the upper mantle would have to proceed by some mechanism other than the migration of melt along channels developed along wetted intergranular surfaces.