Archaeologists who specialise in stone artefact analysis focus on the features created when stone fractures. These features, called ‘attributes’, result from the mechanics of fracture in brittle materials. Engineers who study fracture mechanics have modelled and described the fracturing process in detail.
Stone tool-making involves removing small pieces of stone, called flakes, from a larger piece of stone, called the core. When the stoneworker strikes near the edge of the stone, a crack opens, travels through it and then exits, separating the flake from the core. Scientists have modelled the process of fracture by dividing it into three phases: 1) the initiation phase, when the crack starts; 2) the propagation phase, as the crack travels through the stone; and 3) the termination phase, when the crack exits the stone. The way that the crack starts determines how a flake propagates and terminates, and the stoneworker can carefully adjust the way they initiate the crack to achieve the effect that they want.
A crack can be initiated in three ways: conchoidally, by bending, or by wedging. These initiation types are strongly influenced by the stone-flaking technique. The crack travels through the stone at 600 metres per second or more and the flake detachment is essentially instantaneous, so all of the stoneworker’s control depends on the way they apply the force to the core. Each of the phases of flake formation leaves behind features, or ‘attributes’, on the core and flake. By closely studying these attributes, a specialist—called a lithic analyst—can reconstruct how the stoneworker initiated the flake and why they may have done it that way.