Potassium and Calcium K‐Edge XANES in Chemical Compounds and Minerals: Implications for Geological Phase Identification

Abstract

Potassium (K) and calcium (Ca) K‐edge X‐ray adsorption near‐edge (XANES) spectroscopy were performed on thirty‐three chemical compounds and geological materials, including chemical reagents, organometallic compounds, silicates, carbonates and igneous rock reference materials. The results confirm that the fine structure of the K‐edges for specimens is unique and distinguishable. The results suggest that compositional and local atomic variations strongly regulate spectral characteristics. Acquired XANES spectra with the library of distinctive spectral features of model references approve the fingerprint identification of different phases of K and Ca involved in geological materials. Moreover, this reveals that typical compositional changes in geological samples could strongly affect spectral features. As an example, we quantitatively determined the silicate species of K and Ca in two igneous rock reference materials by linear combination fitting. The dominant hosts and molecular environments of K and Ca can be interpreted based on pre‐edge/post‐edge peak position, intensity, shifts and resonance features, thus improving the understanding of the (bio)geochemical cycling, partitioning and isotopic fractionation of K and Ca. The outcomes serve as a complementary database for a vast number of scientific contexts, including aspects of geological and environment sciences.