Rietveld refinement strategy for quantitative phase analysis of partially amorphous zeolitized tuffaceous rocks

Abstract

The Rietveld method has become one of the most popular methods in quantitative mineralogical analysis based on X-ray powder diffraction. An estimate of the amorphous phase content can be made by introducing a known amount of an appropriate internal standard. This method was applied to a selected set of zeolitized tuffaceous rocks to develop guidelines for Rietveld quantitative phase analysis in complex mixtures. A local sensitivity analysis of selected refinable parameters was performed and phase abundance results for synchrotron and laboratory based X-ray diffraction data collection were compared. The calculated amorphous phase fraction showed a very high sensitivity towards the refined amount of internal standard, in particular when small amounts of amorphous phase were encountered in the samples. Optimal reproducibility of phase abundance results was obtained when a sufficient number of background polynomials was employed and the internal standard thermal parameters were not refined. A very good correlation between laboratory and synchrotron data was achieved when the communicated refinement strategy was followed, supporting the use of laboratory equipment for routine quantitative mineralogical analysis.