Stone Tool Analysis: Heat fracture
Rapid thermal expansion in brittle stones—such as flint and chert—can cause cracks to form internally. These initiate at flaws where the differential rates of expansion create fields of stress. If the stress overcomes the material’s elasticity, the stone will break. This is often caused by exposure to the intense heat of fires, but it can also occur in freeze-thaw cycles and on stones exposed on the surface in deserts.
Stone that is raised to extreme temperatures can crenate into cuboidal and angular pieces. Quartz undergoes phase changes from about 573º C, resulting in an increase in expansion that exacerbates internal fracturing in silicious stones. These fractures are irreversible and undesirable for stoneworking.