Mineralogical investigations on an Indian glauconitic sandstone of Madhya Pradesh state

Abstract

Glauconitic sandstone occurring in Majhgawan, Madhya Pradesh (India) was examined to study the composition and association of glauconite with different minerals. The study was carried out by petrographic investigation, X-ray powder diffraction (XRD), simultaneous thermal analyses (STA) and infrared (IR) spectral method. With a majority of quartz grains, glauconite pellets (both clear and limonitized) along with a smaller percentage of potash feldspars and mica minerals are found embedded in a mixed ferruginous and glauconitic matrix. The nature of (001), (020) and (003) spacings as found in the XRD patterns obtained for different fractions of the sample suggests the presence of disordered glauconite in the glauconitic sandstone. XRD identification is amply supported by endotherms at 560°C in differential thermal analysis (DTA) curves representing loss of constitutional water from the glauconite structure. Appearance of endotherms in DTA curves in the 275–353°C temperature range indicates the presence of poorly crystalline goethite, which is also substantiated by the absence of characterstic d lines of goethite in XRD patterns. On heating the sample to 760°C, (001) reflection of kaolinite disappears and further heating to 1000°C causes collapse of the glauconite structure also. Formation of hematite takes place in the sample heat-treated at 1000°C. The results demonstrate a clear rising trend of glauconite and kaolinite contents and diminishing proportions of quartz with the reduction in the particle size of the sample.