Weathering of biotite supplies nutrients such as K+ and weathers into vermiculite/montmorillonite or kaolinite, which have varying influences on soil properties and characteristics. This study was conducted to determine if the weathering mechanisms of biotite are controlled by temperature, or if other factors, such as vegetation or leaching intensity dominantly influence the weathering process. A column study investigation was conducted to assess the influence of different acids, simulated rainfall rates, surface horizons, and temperature on the weathering and cation release of biotite. A field investigation was also conducted on the clay mineral fraction of soils in Grayson County, VA formed above biotite granite. Selected acid leachates did show a greater Al+3, Fe+2, and Si+4 release with organic acids (ascorbic, citric, and fulvic) than that with hydrochloric acid treatment at high leachate rates. Loss of K+ is greater with ascorbic acid than all other acids at high leachate rates. Leachate rate interaction with low temperature was an influencing factor in cation release. Field investigations revealed a greater weathering intensity at high elevations evidenced by; (i) higher clay content, (ii) a dominance of 2:1 minerals, (iii) greater surface area in the upper horizons, (iv) minerals indicative of later stages in the biotite weathering mechanism, and (v) precipitation of halloysite in the C horizon at the high elevation site where temperature is lower and a suspected higher leaching intensity occur. / Master of Science

Phosphorus (P), a necessary plant and animal nutrient, can also lead to eutrophication of fresh waters when in excess. Appropriate P management is necessary to prevent fresh water pollution. Mineralogy of soil clays has been shown to affect P adsorption, desorption, and movement through soils. Specifically, hydroxy-interlayered minerals have been shown to adsorb and retain inorganic P in soil systems. This study was designed to determine the sorption and desorption characteristics of inorganic, organic, and mixed forms of P interacting with soil hydroxy-interlayered vermiculites (HIV) and smectites (HIS), and compare the findings to sorption and desorption processes of natural aluminum (Al) and Iron (Fe) hydroxide minerals. Results indicate natural Al and Fe hydroxide minerals sorbed and retained P more strongly than hydroxy-interlayered minerals in our samples and inositol hexakisphosphate was more highly sorbed and retained than inorganic P.