Stone Tool Analysis: Propagation

Bipolar core Mercer chert

Once a crack is initiated, it advances through the stone subject to compression force down the length of the flake and shearing force tearing the flake away from the core.  These forces control the   way the crack expands, or ‘propagates’, through the stone.  Attributes of flake propagation can be seen on the ventral surfaces of flakes and their corresponding negative scars on cores.

Undulations

Compression force operates down the length of the flake, stiffening it, and shearing force separates the flake from the core; these two forces operate at right angles to each other, and when approximately balanced, the crack travels parallel to the core face.  The balance shifts back-and-forth as the crack grows however, favouring one force until pulled back by the other force, and this results in an undulating crack path.  

Bipolar core, Indiana

Bipolar Core

Levallois Nubian re-do silver

Levallois Core

Axe, Flint Jack 1

Modern Art, Flint Jack

Kanzi flake

Modern Art, Kanzi the Bonobo

Hackles

Hackles are linear features found at the edge of a flake’s ventral surface or at the edges of flake scars.  They radiate outward from the point of force application.  Hackles are also known as striations, lances, or marginal fissures in the archaeological literature, and forensic scientists and fractographic engineers refer to them as hachures.  

Large flake, Hat Head

Flake

Bottle glass flake 2, Australia

Glass Flake

Bottle glass flake 1, Australia

Glass Flake

Eraillure

Once a crack is initiated, it advances through the stone subject to compression force down the length of the flake and shearing force tearing the flake away from the core.  These forces control the   way the crack expands, or ‘propagates’, through the stone.  Attributes of flake propagation can be seen on the ventral surfaces of flakes and their corresponding negative scars on cores.

Flake blank core, Mithaka

Core on Flake

Flake, Italy AIA

Flake

Juan knife Selwyn 1

Juan Knife

Siret Fracture

A siret fracture, named after the famous French archaeologist Louis Siret, is a secondary crack that splits the flake as it detaches from the core.  

Ukraine flake Oleksandr

Flake

Flake, siret arris

Flake

Kanzi flake

Modern Art, Kanzi the Bonobo

Flake, block-on-block, Mithaka

Quarry Debris