Mineralogy of fine sand and clay fractions of two pedons of basaltic region of Medak district of Andhra Pradesh was investigated using petrography, X-ray diffraction technique (XRD) and differential thermal analysis (DTA). Light minerals constituted bulk of the sand fraction and comprised quartz, orthoclase and plagioclase feldspars and mica in order of their abundance. Heavy minerals contributed very small fraction and were dominated by opaque minerals, hornblende, augite and epidote. Mineralogy of clay fraction by XRD and DTA showed the dominance of smectites with a small fraction of kaolinite. The presence of weatherable minerals like hornblende and augite indicated that the soils are moderately weathered and are of medium age. Both smectite and kaolinite were possibly formed in an earlier geological period with more rainfall and greater fluctuation in temperature and were preserved to the present day because of the climate change from humid to semi-arid during the Plio-Pleistocene transition period.
Mineralogy of sand and clay, basalt, Vertisols, Petrography, XRD, DTA
