Geochemical properties and the nature of kaolin and iron oxides in upland oxisols and ultisols under a tropical monsoonal climate, Thailand.

摘要

Fifty samples from genetic horizons of 17 soils on various parent materials under a tropical monsoonal climate in Thailand were analyzed for chemical and mineralogical properties of the clay-sized minerals. These Oxisols and Ultisols have kaolinite as the dominant clay mineral and various amounts of accessory minerals with higher amounts of sesquioxide minerals in Oxisols. The crystal size of kaolinite and iron oxides is smaller for basaltic soils relative to soils on granite and sedimentary rocks. Halloysite tubes occur in some soil clays particularly for basaltic soils and these soils also contain gibbsite. Oxisols derived from basalt have relatively higher contents of Fe, Ti, Mg, Mn, Ba, Be, Bi, Ce, Co, Cr, Cu, Ga, La, Nd, Ni, Sc, Sr and Zn. Statistical analysis indicates a lithosequence where soil parent material is the main factor influencing the mineralogical and chemical properties of the clay fraction of these soils.