Electron Microprobe Analysis of Weathered Florida Chert

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Abstract
Underlying paleo-Indian period artifacts, deeply weathered chert implements have been recovered in Florida from a sandy clay horizon heretofore considered culturally sterile. Although the stratigraphic position of the stone implements in the sandy clay deposit has been demonstrated without question, dating has been a problem because no carbon-containing material has been preserved. Thus experiments were undertaken to investigate the environmental conditions under which the stone artifacts have weathered and the time required for the given extent of weathering. The electron microprobe was used to evaluate the surface compositional changes that occur in Florida chert during weathering. The patina of a chert surface exposed to an acid environment was found to be depleted of iron to a depth of ∼ 600μm. The mechanism through which Fe is leached from the surface is thought to be a diffusion-controlled process in which the depth of leaching is proportional to the square root of exposure time. This may provide a means of dating artifacts fashioned from these cherts.