The results from an emerging method of nondestructive grain boundary characterization, with unprecedented sensitivity to neighbor-grain misorientation and grain boundary morphology are reported. The method utilizes differential aperture X-ray microscopy to determine the local crystallographic orientation of submicron volumes within polycrystalline materials. Initial measurements are described for a recrystallized Ni sample where the grain boundary type was identified at 85 grain boundaries within the framework of an ideal coincident site lattice (CSL) model. The remarkable resolution of this method is demonstrated by the <0.03 degrees deviations of misorientation measured for Sigma3 (twin) boundaries. Because of its high angular and spatial resolution, this new approach to grain boundary characterization can provide quantitative tests of grain boundary models with new insights for grain boundary engineering efforts.