X-ray absorption spectroscopy (XAS) is a technique used to study the electronic structure and local atomic environment of materials by measuring the absorption of X-rays as a function of energy. XAS is significant in mineralogy and geochemistry for understanding the oxidation states, coordination chemistry, and bonding environments of elements in minerals and other materials.
Source Koningsberger, D. C., & Prins, R. (1988). “X-ray Absorption: Principles, Applications, Techniques of EXAFS, SEXAFS, and XANES.” Wiley.