Advancing x-ray diffraction based mineralogy in Estonian limestones [Magistritöö. Juhendaja: R. Hints; kaasjuhendaja: M. Karpov]

This thesis aimed to determine the origin of K-feldspar from Estonian limestone by studying its crystallographic variations and developing a methodology for assessing the crystallochemistry of calcite
based on lattice parameters and compositional analyses. A second aim was to evaluate different sample preparation techniques for powder X-ray diffraction (XRD) analyses with respect to preferred
orientations.

Five limestone samples from different depths of the Viki drill core (Saaremaa) were prepared using several methods. The insoluble residue, composed mainly of silicate minerals, was separated from calcite and dolomite. The insoluble residue was divided into five fractions (clay fraction and four grain-size fractions). The fractions were analyzed in detail using X-ray diffraction and X-ray fluorescence spectroscopy (XRF) to acquire the mineralogical and elemental compositions.

The lattice parameters of calcite were calculated using EVA and TOPAS software, focusing primarily on the latter as it has the capability of Rietveld refinement. The development of preferred orientations
depending on the sample preparation method was analysed and discussed. Lattice parameters of K-feldspar were calculated and used to derive the order of Al-Si distribution depending on the grain size.

The results suggest that, in general, the tested method for determining composition of calcite works but needs further refinement. The question regarding the origin of the K-feldspars within the analysed limestones could not be unambiguously answered. However, it was found that the Al-Si distribution of K-feldspars becomes more disordered as the fractions become finer.
The overall results of the study opened up novel prospects for further research on the physiochemical properties and development pathways of Estonian limestones.