Silcrete

Bifacial silcrete point from Blombos Cave, South Africa, Middle Stone Age
(71,000 BCE) (scale bar = 5cm)

Silcrete is an indurated soil duricrust formed when silica is dissolved and resolidifies as a cement. It is a hard and resistant material, and though different in origin and nature, appears similar to quartzite. It is common in the arid regions of Australia, often forming the resistant cap rock on features like breakaways.

In Australia, silcrete was widely used by Aboriginal people for stone tool manufacture, and as such, it was a tradeable commodity, and silcrete tools can be found in areas that have no silcrete groundmass at all, similar to the European use of flint. Tools made out of silcrete which has not been heat treated are difficult to make with flintknapping techniques. It is widely believed by stone tool experts that the technology to treat silcrete by burying under a hot fire was known 25,000 years ago in Europe. Heating changes the stone structure making it more easily flaked. This process may have been the first use of so-called pyrotechnology by early mankind.

In South Africa at Pinnacle Point researchers have determined that two types of silcrete tools were developed between 60,000 and 80,000 years ago and used the heat treatment technique. There is evidence to suggest the technique may have been known as early as 164,000 years ago.