DETECTING HEAT-TREATMENT ON SILCRETE - EXPERIMENTS WITH METHODS

We describe experiments aimed at detecting heat treatment of silcrete, a siliceous rock of inhomogeneous lithology widely used in prehistori c Australia. Our samples (N=66) come from eastern New South Wales. Two methods widely used on other materials are found to be inadequate: sc anning electron microscope (SEM) analyses allow conflicting interpreta tions of the same piece of material, while colour changes an too varia ble to be a reliable indicator. Two other methods are more reliable: i ncrease in lustre is rare, but clearly indicates heat treatment when i ts thermal origin is certain; palaeomagnetism assessments of modern (N =18) and archaeological (N=23) samples show that while the method does not give false positives, it indicates heating and not necessarily he at treatment. A combination of palaeomagnetism and lustre assessments is recommended. (C) 1997 Academic Press Limited.