Investigation of silica polymorphs stratified in siliceous geode using FTIR and XRD methods

The study aims to differentiate the silica forms stratified in the siliceous geodes using infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The water content (total water, H2Omol and Si-OH) in SiO2. nH2O forms are used as the fingerprint for the different varieties of the silica morphs. For this reason, an irregular botryoidal spherical shape siliceous geode formed from alternative silica forms collected from Early–Late Eocene carbonate sediments of the Ratga Formation located in the Western Desert of Iraq were mineralogically investigated. The FTIR and XRD as authoritative tools that have been used together with the water content to enhance the distinction between crystalline and non-crystalline silica forms. Quartzine, quartz, chalcedony opal-A, opal-C, and opal-CT have been identified in different layers of geode in addition to calcite lining the geode center.