The Genesis of Gemstone based on Pillow Lava Primary Structure: A Case Study from Kumbang Formation, Limbasari

Abstract

Abstract Gemstone/Jasper is an ornamental rock included in the quartz (SiO2) microcrystalline chalcedony variety. Jasper is translucent, has a microcrystal structure, and consists of several mixes of other minerals resulting in appealing color and patterns. In general, Jasper forms as a result of hydrothermal activity controlled by geological structure (secondary structure). On the other hand, Jasper is formed in Limbasari, controlled by a primary structure on pillow lava. The methods used are field data collection, petrography, and XRF (X-Ray Fluorescence). From the data collected in the field and results from petrography analysis and genesis geochemistry. We can infer that the Jasper found in the research site can be called Peperite. The jasper there is a result of unconsolidated tuff deposits still in the form of wet deposits rolled up by the movement of pillow lava and sealed in the gaps of the pillow lava primary structure, starting a partial melting process, and then cooled swiftly, resulting in glassy texture.