PHYSICAL, CHEMICAL, AND MINERALOGICAL CHARACTERIZATION OF VERTISOLS TO DETERMINE THEIR PARENT MATERIAL

The response of soils to weathering processes depends upon their parent material. Proper identification of the primary and secondary minerals in Vertisols provides information about the parent material that gives origin to these soils. Thus, the objectives of this study were 1) to determine the physical and chemical properties of Vertisols in order to characterize and classify them; 2) to identify their primary and secondary minerals to ascertain the type of parent material that gave origin to these soils; and 3) to determine the type of rock that produces Vertisols. Two types of Vertisols were studied: one of igneous origin and dark color, and the other of sedimentary origin and pale light color. Soils of igneous origin were classified as Chromic Haplusterts, Typic Haplusterts, and Mollic Ustifluvents. Sedimentary origin soils were classified as Chromic Calciusterts and Typic Calciustolls. Dominant mineralogy of the soils of igneous origin in the sand fraction was comprised of volcanic glass (47%), quartz (31%), and feldspars (22%). Amorphous materials, smectites, vermiculites, illites, and cristobalites dominated the clay fraction. In contrast, in the soils of sedimentary origin the sand fraction was composed of calcite (64%), quartz (34%), and feldspars (2%). Smectites, vermiculites, quartzes, and feldspars composed the clay fraction. The parent material of the igneous soils was rhyolite, while the sedimentary soils were derived from limestone and sediments with high calcium carbonate contents.