A study on mineralogy of soils under two parent rocks in higher rainfall areas of Iran

摘要

Morphology, mineralogy and geochemistry of soils derived from granite and andesitic basalt was investigated in western part of Lahijan. Two representative soil pedons were selected in mountain landform. Mineral weathering was characterized by petrographic microscope and comparison was made with total elemental analysis (XRF) and X-ray analysis (XRD).All evidences showed that there is a close structured relationship between the host mineral and the weathering products however, the weathered rock has also been hydrothermally altered. Mineral composition (confirmed by thin section and XRD) in granite were quartz, orthoclase (including perthitizing zone) albitic plagioclase and minor amount of biotite however in andesitic basalt were pyroxene, olivine,amphibole, plagioclase (labradorite) and quartz. Furthermore, sericite, chlorite, smectite (in soils from andesitic basalt) and vermiculite were the most alteration products. Total elemental content of Ca, Mg and Fe as well as solum thickness in field observation and clay mineral content were higher in soils from andesitic basalt which can be attributed to the presence of more susceptible ferromagnesian minerals to weathering.