Flaking Properties, Petrology and Use of Polish Flint
Domanski, Marian, Webb, John A., Antiquity
From the Middle Palaeolithic to Early Bronze Age, flint was used extensively in Poland for stone tool manufacture (Lech 1981; Balcer 1983). Three different flint types were mined around the Holy Cross Mountains of southeastern Poland (FIGURE 1) (chocolate, grey white-spotted and banded flint), each for a different purpose (short or long blades and partly polished or polished axes). The reasons for the separate usage for each flint type relate to both mechanical and physical properties and aesthetic appearance.
[Figure 1 ILLUSTRATION OMITTED]
Recent experimental studies (Domanski & Webb 1992; Domanski et al. 1994) have used mechanical properties, particularly fracture toughness, to define the flaking properties of stone artefact materials. These studies showed that fracture toughness, which measures the resistance of a material to catastrophic fracture propagation, is the most objective and important measure of the quality of stone tool materials. Lithic materials most amenable to blade manufacture and pressure flaking (obsidian) have low values of fracture toughness, whereas those shaped into axes by pecking and grinding (greenstone) have very high values (FIGURE 2) (Domanski et al. 1994: 203, figure 5).
[Figure 2 ILLUSTRATION OMITTED]
These results are here applied to the three different types of Polish flint from the Holy Cross Mountains, in order to relate the different uses to which these flints were put to their fracture toughness and petrology. However, before discussing the Polish flints in detail, it is first necessary to review the general characteristics of artefact materials used for blade and ground tool technology, and the differences between them.
Flaking properties of raw materials used in blade technology
For blade manufacture, the lithic materials normally favoured were homogenous and isotropic microcrystalline siliceous lithologies. In these rock types, the lack of direction-dependent properties means that flake detachment is determined only by the stress distribution during the flaking event, and is more readily controlled by the knapper (Cotterell & Kamminga 1987; Crabtree 1968: 457-9).
Raw materials amenable to blade manufacture and pressure flaking have low values of fracture toughness and high rankings of macroscopic uniformity (Domanski et al. 1994: 203, tables 4 & 5). Obsidian is generally regarded as the easiest material to work for flaked stone tools (Bordes 1969: 14; Callahan 1979: table 3), because it requires less force than other lithologies to detach flakes, and it has a low fracture toughness (median 24-27 MPa.[mm.sup.1/2]) and high macroscopic uniformity (Domanski et al. 1994: table 5). Glass Buttes obsidian of central Oregon was graded at 1.0 on Callahan's scale of `ease of workability' (Callahan 1979: table 3), and has a fracture toughness of about 26 MPa.[mm.sup.1/2] (FIGURE 2).
Flaking properties of lithologies used in ground tool technology
Raw materials used for ground stone cutting tools are shaped by pecking and grinding. During pecking hundreds of sharp blows are delivered to the blank, which must be very tough, resistant to fracture and free of cracks and other flaws (Fenton 1984: 223). Fine- to medium-grained rocks with strongly interlocking textures or strong intergranular bonds are preferred (Fenton 1984: 231), e.g. metamorphosed basic volcanics (greenstones). The low quartz content of greenstones also makes them softer and easy to grind (Dickson 1981: 106-7). For example, Mount William greenstone of southeastern Australia was widely used to make ground-edge axes (McBryde 1978: 355-6). This lithology is a fine-grained metabasalt composed of interlocking, randomly oriented actinolite crystals, and has very high values of fracture toughness (median 105-130 MPa.[mm.sup.1/2]) (FIGURE 2) and high rankings of macroscopic uniformity (Domafiski et al. 1994: 193,197, table 6), explaining its mechanical superiority in the manufacture of ground-edge axes. …