An SEM study of phyllosilicates in a Westphalian Coal Measures sandstone using back-scattered electron imaging and wavelength dispersive spectral analysis

Abstract

Back-scattered electron imaging (BEI) made in a Jeol JXA 733 SEM was used in combination with wavelength dispersive spectral (WDS) analysis to study phyllosilicate minerals in thin foils and polished thin sections of Coal Measures (Westphalian) sandstones from the East Midlands, U.K. Detrital chlorite grains up to 500 μm occur intergrown with hydromuscovite and kaolinite. Detrital muscovite grains have undergone incipient alteration to illite and occur intergrown with chlorite and kaolinite. In addition, kaolinite occurs as pore-filling books of plates. All kaolinite is authigenic, though it is not clear whether it replaces the chlorite or muscovite intergrowths, or is simply intergrown with them. Analyses obtained from thin foils and polished thin foils, are more reliable than analyses obtained from fracture surface SEM samples because artefactual additions to the characteristic spectra are minimized.