Revealing the rock heterogeneity in Sebau, Lombok Island by applying morphological and elemental composition analyses

Abstract

Lombok Island is situated in east Indonesia. Its heterogeneity is very complex. It is one of the seismically and volcanically active regions in Indonesia. Several earthquakes occurred on Lombok Island in July-August 2018. Lombok Island is also known as the place of an active volcano (Mt. Rinjani) and geothermal resources in Indonesia. We applied the morphological and elemental composition analyses to know in more detail the rock heterogeneity in Lombok Island by using X-ray fluorescence (XRF), field emission-scanning electron microscopy/energy-dispersive X-ray spectroscopy (FESEM-EDS), and X-ray Powder Diffraction (XRD). In this study, we chose the Sebau hot springs as the study area and collected the rock sample in the study area in August 2022. The FESEM-EDS result shows that the crystalline structures of the rock sample have a compact, unconsolidated, and fine structure with some layers. The significant elements of the rock samples by applying XRF analysis are Si (36.91%) and Fe (30.787%). It is also supported by the XRD analysis that revealed the dominant compounds in the rock samples are pyrite (FeS2) and cristobalite (SiO2). Therefore, there is an indication of the study area is the surface manifestation of the past Mount Rinjani volcanic activity.