Accelerated Weathering of Secondary Minerals on Ratu Crater Toposequences of Tangkuban Parahu Volcano, West Java

Abstract

The crater environment of Ratu Crater, Tangkuban Parahu Volcano was largely shaped by chemical processes that occurred in the geothermal centre in the form of fumarole and solfatar. A range of five representative profiles were identified in the toposequences of the crater i.e. A (toeslope), B, D (backslope), G and J (summit). Soil samples were physically, chemically, and mineralogically analysed. Mineralogical analysis showed that the sand fraction of heavy minerals (specific gravity> 2.87) were opaque, augite, and hipersten, while light minerals (specific gravity< 2.87) were volcanic glass, zeolite, andesin, labradorite, bitownite and rock fragments. Extraction with oxalate and pyrophosphate showed Profile D (backslope) to contain the highest mineral content of allophane (1.414 %), imogolite (0.391 %), and ferrihydrite (2,091 %). The lowest content was found in Profile A (toeslope), which had a smaller content than Profile J (summit). XRD analysis results (no treatment) showed that all profiles of A, B, D, G, J had almost the same reflection pattern consisting of calcite (3.03 Å), cristobalite (4.04 Å), feldspar (3.1-3.25 Å, gibbsite (4.85 Å), kaolinite (7.1 Å) and quartz (3.34, 4.27 Å). XRD analysis (Mg+glycol) of the profiles showed each profile to be mostly dominated by non-crystalline minerals (amorphous); however Profile J (Summit) and Profile A (toeslope) were dominated by crystalline minerals that had been developed from amorphous minerals, i.e. mineral 2:1 (smectite and chlorite) and mineral 1:1 (halloysite and kaolinite)