In
lithic analysis in
archaeology the
cortex is the outer layer of
rock formed on the exterior of raw materials by chemical and mechanical weathering processes. It is often recorded on the
dorsal surface of
flakes using a three class system: primary, secondary, and tertiary. The amount of cortex present on artifacts in an archaeological assemblage may indicate the extent of
lithic reduction that has occurred. Primary, secondary, and tertiary designations for flakes are generally determined by relative amounts of cortex presented on the dorsal surface. Some archaeologists classify flakes with no cortex as tertiary, flakes with some cortex as secondary, and flakes with all cortex as primary, whereas others may distinctions at every third or half of the dorsal surface covered. Differences in how archaeologists classify the amount of cortex and the results of
experimental archaeological tests demonstrating moderate correlation between amount of cortex and stage of reduction, have limited the validity of assumptions based on amount of cortex solely.