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)
