It's as the title of the question states. To be specific, I'm wondering if there are any free online repositories where I can download (.csv or .txt. or .xsl) files for x-ray diffraction (XRD) data.
The Materials Project, a computational database, also calculations X-ray diffraction patterns and absorption patterns (disclosure, I'm on the Materials Project staff).
You can also generate your own once you have a crystal structure, many tools exist to generate a diffraction pattern, for example pymatgen using the
XRDCalculator, though these will need to be artificially broadened if you want something that looks like an experimental pattern.
For x-ray diffraction and Raman spectroscopy data of minerals, you may try https://rruff.info/
According to their site, "The RRUFF™ Project is creating a complete set of high quality spectral data from well characterized minerals and is developing the technology to share this information with the world. Our collected data provides a standard for mineralogists, geoscientists, gemologists and the general public for the identification of minerals both on earth and for planetary exploration."