Stone Tool Analysis: Wedging initiation
A wedging initiation occurs when a microscopic particle is driven into a pre-existing micro-crack in the stone. This wedges open the micro-crack and initiates the main fracture, which then runs down the face of the core.
Wedging initiations tend to occur when a stone is struck with a super-hard blow, or when the core is supported on a hard anvil. The strength of the forces involved, relative to the size of the core—or the compression effects of a core resting on a hard anvil—result in a highly unstable crack path and exceptionally prominent and closely-spaced undulations. A wedge-initiated scar is flat rather than convex, lacks a bulb of force, and has a ‘sheared’ appearance.