The results of 96 experiments to investigate the behavior of "nonvolatile" sulfides below their melting points and in the absence of free O are reported. Cylindrical pellets of copper sulfide heated in contact with similar pellets of iron sulfide, in N, reacted at temperatures above 300 degrees C. to form layers of bornite and chalcopyrite, mainly in the FeS pellets. The thickness of the layers of reaction products increased with time and temperature. Rock discs placed between 2 such pellets were veined by chalcocite. Pyrite grains were replaced by chalcocite, bornite, and chalcopyrite. Copper sulfide heated with Fe-rich chlorite showed some reaction at 550 degrees C., but biotite, epidote, bronzite, augite, siderite, and calcite showed none. CuS heated at 300 degrees C. and at higher temperatures, recrystallized to chalcocite and digenite. If placed in a temperature gradient above this temperature, it also moved toward the lower temperature at a very appreciable rate. If excess S was removed, no appreciable migration occurred. Iron sulfide and a mixture of CuS and PbS also showed appreciable movement in similar circumstances. Volatile transfer of Fe and Cu from sulfides was recorded at 550 degrees C. for Fe and 675 degrees C. for Cu.