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Dust grain composition, sizes, and spatial distribution can be directly measured with high resolution X-ray imaging and spectroscopy. Dust in the foreground of bright point sources will scatter X-rays through small angles, producing a diffuse `halo' image. The scattering cross-section is most sensitive to large dust grains, which are typically missed in UV, optical, and infrared studies. The dust-to-gas mass ratio and elemental constituents of dust grains can also be determined from X-ray spectroscopy. I demonstrate how a Bayesian analysis of the scattering halo around Cyg X-3 yields a grain size distribution and mass ratio that does not match properties typically assumed of Galactic dust. Finally, I will discuss the prospects for using quasars to measure the cosmic density of dust grains in intergalactic space.