Mineralogy and sand surface morphology of some volcanic ash soils from West Sumatra, Indonesia
1998
Fauziah Ishak | Shamshuddin Jusop | Van Ranst, E. | Fiantis, D. | Siti Zauyah Darus
Volcanic ash soils from Mt. Marapi and Mt. Pasaman in West Sumatra, Indonesia, were studied to characterize their mineralogy and the surface morphology of the sand grains. The minerals in the sand grains include quartz, etched feldspars, halloysite and glass having different surface morphology. Halloysite exists as tubular crystals on the weathered grain surface. SEM-EDX gave strong peaks of Si and Al, but a weak peak of Fe, confirming the presence of halloysite. The clay fraction composes mainly of noncrystalline materials, cristobalite, feldspars and halloysite. Allophane is abundant in this fraction. Soils of the Mt Pasaman have some gibbsite, while those of the Mt. Marapi have opaline silica in the surface horizons. The abundance of opaline silica tends to decrease with the age of the volcanic ash soils. The sand particles have a large variety of morphologies. The morphological features observed are bubblels, pitted, curve platy and amorphous spheres to cryptocrystalline overgrowth. Some of the sand grains are coated with irregular and spherical-shaped aggregates.
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