Australia: The Land Where Time Began

A biography of the Australian continent 

There are 2 silcrete varieties in the Gorge Quarry, fine-grained and medium-grained, the medium-grained silcrete having irregular granular fracture, and is of a light grey or greenish yellow colour. Its microfabric is grain-supported and consists of rounded to sub-angular quartz clasts, that are mostly of medium-sand-size in a microcrystalline quartz matrix (Table 1 & fig. 2 (C), Source 1), and many small cavities up to 3 mm in diameter, with an occasional quartz grain that can be up to 2 mm in diameter.

Conchoidal fracture surfaces are present on the uniform grey fine-grained silcrete from Gorge Quarry. In a microcrystalline quartz matrix, it has a grain-supported microfabric consisting of subangular quartz clasts that are well-sorted, and are mainly of a very fine-sand-size, though occasionally they are coarse-grained (Table 2 & fig. 2 (D), Source 1), with patches of chalcedonic silica.

The median fracture toughness of the Gorge Quarry silcrete, that is medium-grained, is lower than that of the Olive Downs Quarry silcrete, that is microcrystalline, though a considerable amount of overlap is present (Table 2, Source 1). The authors suggest the Olive Downs Quarry silcrete  probably has values of compressive and tensile strength compared to microcrystalline silcrete, as in Australia nearly all medium-grained silcretes that have been tested have compressive and tensile strength that is low to medium (Table 2, Source 1), while the fine-grained silcrete of the Gorge Quarry has a fracture toughness that is relatively high (Median 87 MPa.mm^1/2) and a low index of stiffness (7.5).

For more detailed information and illustrations see Source 1

Sources & Further reading

1. Webb, J.A. & Domanski, M, The Relationship Between Lithology, Flaking Properties & Artefact Manufacture for Australian Silcretes, Archaeometry, Oxford University, Archaeometry, 50, 4 (2008) 555-575

Stone tools