Characterisation and genesis of the chalcedony occurring within the Deccan lava flows of the LIT hill, Nagpur, India

Abstract

The Deccan trap basaltic lava flows host a plethora of secondary minerals, notably zeolites, quartz and calcite. These minerals occupy the vesicles and cavities that are formed during the solidification of the lava flows. Much attention has been given to beautifully developed zeolites of the Deccan traps and well-crystallised quartz varieties such as rosy quartz and amethyst. However, a group of minerals consisting of cryptocrystalline and amorphous silica did not receive much attention despite their consistent occurrence in all parts of the Deccan large igneous province. The freshly exposed samples of the chalcedonic silica occurring in the vesicular basalt at the Laxminarayan Institute of Technology (LIT) hill, Nagpur University Campus, were studied, one of which was studied in detail using X-ray diffraction analysis, differential thermal analysis, thermogravimetric analysis, Fourier transform infrared and scanning electron microscope–energy dispersive spectroscopy. The present study has demonstrated that the secondary silica occupying vesicles in the basaltic lava flows was length-fast chalcedony showing fibrous morphology overprinted by grainy morphology. It was concluded that the mother fluid was a hot (~100–300°C) aqueous solution, which was acidic in nature and high in sulphur, probably derived from the host Deccan trap basaltic magma itself.