Silcretes: Insights into the occurrences and formation of materials sourced for stone tool making

Abstract Silcretes are clearly observed and abundant as components of paleolandscapes on several continents. Mechanisms for the formation of several varieties of silcrete, with specific relationships to paleolandscapes, are described. Each type of silcrete displays particular morphological features in its profile in the paleo-regolith, and these features provide pointers to its origin via mechanisms of absolute or relative accumulation of silica in specific environments relating to groundwater or soil-water hydrology. The characters of silcrete varieties that may have triggered the interest of prehistoric peoples to exploit them for manufacturing stone tools, and which control knappability, include granulometry and the specific nature of silica cements. The successions of silica precipitation and recrystallisation events are clearly evident as a complex of micromorphological features that provide clues to the hydrological environment and its geochemistry at the time or times of silicification. Examples are given of the distribution of different silcrete facies, which could have had differing values for exploitation for stone tool production, in modern-day landscapes in France and Australia.