Silcrete

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. Compare the European use of flint.