added by archaeologs A relative dating technique used on bone. Bone absorbs fluorine from groundwater at a rate proportional to the time since burial - if groundwater migration rates remain constant. Fluorine concentrations are chemically analyzed by the gradual combination of fluorine in groundwater with the calcium phosphate of the buried bone material. Bones from the same stratigraphical context can be dated relatively by comparison of their fluorine content. The Piltdown forgery was finally exposed by this method.