Rietveld structure refinement of microcline

Compared with single-crystal X-ray diffraction, extracting structural data from X-ray powder diffraction (XRPD) seems meaningless for minerals with an available single crystal, such as alkali feldspar. However, alkali feldspar is highly abundant on Earth, and the feldspar structure is important in geology. Thus, the potential of extracting structural parameters from powder diffraction data collected using conventional Bragg-Brentano XRPD (BB-XRPD) with CuKalpha radiation is worthy of exploration. BB-XRPD may be the most extensively used instrument in the laboratory and has a major advantage in terms of cost and convenience. Accordingly, by combining the Rietveld method with the General Structure Analysis System (GSAS) of BB-XRPD, a microcline structure in a natural feldspar sample with two minor impurities was refined for the first time. To extract high-quality structural data, a formula related to Si/Al-O bond lengths and Si/Al occupancies in terms of the crystal structure database and a new model are sequentially presented. The reliability of the structural data for such a low-symmetry phase as microcline is discussed and established by comparison with published single-crystal data.