Under conditions of a sub-tropical climate and approximately 100 inches of rainfall annually, plagioclase feldspar in the olivine basalt flows of the Koloa series alters directly to gibbsite. Four stages of weathering are outlined. Between stages two and three there is a large and abrupt increase in the percentages of alumina and iron and corresponding impoverishment in silica, calcium, and magnesium. In the fourth stage some of the alumina becomes mobilized, migrates through the leached rock and is redeposited as filling material in fractures and cavities. Some of these concentrations weather out of the lateritic soil and strongly decomposed rock in the form of irregularly shaped nodules of gibbsite.

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