The application of lithic raw material mechanical analysis
in Paleolithic archaeology
ZHOU Zhenyu, HUAN Yong, LIU Wei, DONG Jie
2016, 35(03):
407-417.
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Raw material is commonly considered as a very important element in prehistoric stone tools production. Different raw material has been proved to cause variability in lithic assemblages by influencing the knapping technique and tool types. The knapping properties of raw material have a strong correlation with rock mechanical properties which are determined by factors such as mineral composition, crystal size, density, texture, and degree of weathering, moisture content, etc. For a long time, hardness is taken as only criteria to evaluate the raw material mechanical properties based on a semi-quantitative lithic grade scale. In most cases, “easy”, “good”, are used to describe the high quality raw material by knappers’ subjective sensation. Lithology analysis and mechanical tests have been proved as quantitative approach for mechanical properties of stone raw material. In the past study, four mechanical properties, elastic response, compressive strength, tensile strength, and fracture toughness were selected for testing. Fracture toughness was supposed as the most objective measure of the knapping quality of raw materials. In this paper, the results of lithology mechanical tests have shown that compressive strength is also an objective measure of the raw material quality. Besides that, rock damage processes in compression tests include the initiation, development and nucleation of cracks that can be reflected on strain vs. stress curves. To investigate the mechanical properties of raw material, compression tests were performed using a MTS 810 material testing machine. Specimen cubes were cut out of pebbles from Paleolithic site for the tests. Force is measured by the load cell, and the deformation of the specimen is measured by a COD displacement sensor fixed between two compression plates. This deformation vs. force relationship was then transformed to a strain vs. stress curve. Six kinds of raw material, dolomite, chert, obsidian, quartz, quartzite, and granite, were involved in the compression test. In Shuidonggou site, dolomite shows higher ductility and brittleness than quartz and quartzite. This result implies that dolomite appears better flaking properties than quartz and quartzite in Shuidonggou. Archaeology remains The quartz from Beitaishanmiao site, Hubei and Xujiacheng site, Gansu present the similar lithology mechanical properties, which might be taken as one explanation for that both two sites shows similar raw material utilization and lithic assemblage. In the chert (Daerwo site, Guanyindong site, Guizhou) and obsidian (Japan) specimens we examined, since of the microfissure, both the dispersion of maximum stress and maximum strain is bigger than dolomite, quartz, sand quartzite, and granite. This suggests that, in some case, the macro-crystal rock maybe appears better flaking properties than microcrystal rock, such as chert, flint, and obsidian. In this study, mechanical properties analysis has been proved quite objective method for raw material utilization analysis. We suggest that knapping experiment should be correlated with mechanical tests. Moreover, more mechanical tests with different raw materials from different sites are necessary for the comparative examination and also significant for building a raw material mechanical properties database.
