The formation of weld necks between calcium fluoride crystals at elevated temperature was examined. An etchant selective in revealing dislocation intersections with crystal surfaces indicated massive concentrations of dislocations around the positions where CaF/sub 2/ particles sintered to the surface of larger CaF/sub 2/ crystals. The presence of the dislocations is thought to indicate that plastic flow contributes to the formation of the weld neck. Changes in the rnicrostructure around a small hole in a calcium fluoride powder compact during sintering suggest extensive plastic deformation in the area of the hole. (auth).