X-ray astronomy as a field has only existed for about 60 years, yet has led to some of the most breathtaking discoveries in the last century of astrophysics. In this talk, I will discuss two science frontiers of high resolution X-ray imaging and spectroscopy: (1) the astromineralogy of interstellar dust grains, and (2) the accretion flow of Sgr A*, the supermassive black hole at the center of the Milky Way. The X-ray energy band is sensitive to absorption and emission by all abundant metals in the interstellar medium (ISM), both in gas and dust form, enabling us to answer key questions in dust grain growth and processing. X-ray photoabsorption features observed in high resolution spectra of Galactic X-ray binaries directly reveal the mineral composition of interstellar dust. I will review my work on the heavily obscured Galactic Center sight line, where dust scattering significantly alters the apparent size, spectral shape, and timing of X-ray variable sources. And finally, after 20 years of the Chandra X-ray Observatory, we have released new high resolution spectral data for Sgr A* that will be irreplaceable for the next 10-20 years. I will describe how future X-ray missions — XRISM, ARCUS, Athena, and Lynx — will contribute to each of these topics.