ANDESITE WEATHERING

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Abstract
Summary: Using the isovolumetric method of analysis, it is observed that all major chemical constituents except ferric iron and lattice water suffer loss during weathering of hypersthene‐ and olivine‐andesite to saprolite (weathered rock) in an acid leaching environment. Si, Ca, K, and Na are removed rapidly during the early stages of weathering of both rocks. Mg loss is delayed somewhat because it is found in both rocks in relatively large hypersthene phenocrysts which tend to resist weathering. Total Fe, Al, and Ti show moderate losses during weathering. During weathering of the two rocks, the loss of Si, Al, and total Fe is relatively greater from the hypersthene andesite. This is believed due to greater leaching intensity and greater acidity of leaching solution at the hypersthene andesite location. In addition, more pronounced alternate wetting and drying, which occurs at the olivine‐andesite location, exert a strong influence in stabilizing Fe and Al.