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.
Reference: Koningsberger, D. C., & Prins, R. (1988). “X-ray Absorption: Principles, Applications, Techniques of EXAFS, SEXAFS, and XANES.” Wiley.