School of Earth & Environmental Sciences
Kenna, Lachlan S., Understanding Intra-source and Inter-source Variation on the Success of Silcrete Heat Treatment, BSci Hons, School of Earth & Environmental Sciences, University of Wollongong, 2016.
The study of rapid heating and its effects on silcrete is widely debated, and studies have arrived at competing conclusions regarding factors that determine the success of silcrete rapid heating. Clarifying the potential effect of these various factors is important for furthering our understanding of the role of intentional heat treatment as an engineering strategy employed by early humans for modifying the flaking potential of lithic materials. To this end, this study tests for potential inter- and intra-source variation in the overall fracture rates of silcrete heated under a controlled, rapid heating environment.
The tested silcrete samples were collected from a range of locations within Australia and South Africa; the primary test material were from Bannister’s Point/Mollymook and Bendalong Point on the New South Wales South Coast, and the secondary material came from Mustard Hill and Quartz Valley in the Western Cape region of South Africa. Following Mercieca and Hiscock (2008), silcrete samples were prepared in standardised dimensions and heated rapidly under multiple temperature gradients. Prior to heating, the silcrete samples were characterised by a range of attributes, including weight, material composition, and the block of stone from which the sample was cut. In addition, the geochemical property of a subset of the silcrete samples was examined by non-destructive X-ray florescence. Silcrete samples were placed in an oven pre-heated to 550, 600 and 700 degrees Celsius for a period of one hour before gradual cooling. The degree of heat fracture was quantified by comparing the weight of the largest remaining stone of each heated sample to their corresponding mass prior to heating. Statistical analyses were carried out to examine the influence of sample volume, temperature, and source on the degree of heat-induced fracture.
While the results suggest that sample volume plays a significant role in influencing silcrete heat fracture, the effect varies considerably by source. Specifically, samples from Bendalong Point displayed far greater heat resistance than those of Bannister’s Point/Mollymook. This trend of inter-source variation was also apparent in the South African material, although limited sample size restricts the assessment to visual inspection only. The finding also showed intra-source variation, where different blocks of stone from a single source displayed significant difference in heat fracture ii
under identical conditions. Contrary to expectation, maximum temperature was shown to have an insignificant role on heat fracture variation when the influence of source and sample dimension is controlled.