  We calculate the scattering of X-rays by interstellar dust, for a dust model
that reproduces the observed wavelength-dependent extinction and polarization
of starlight. On interstellar sightlines that produce appreciable starlight
polarization, we predict that the dust-scattered X-ray halo around point
sources will have measurable azimuthal asymmetry due to scattering by
partially-aligned nonspherical grains. We calculate the expected halo
asymmetry. X-ray halo asymmetry provides a new test of interstellar dust
models.
