Hand axe
Tool stone and cortex

The natural external cortex or rind of the tool stone, which is due to erosion and the physical-chemical alterations of weathering, is different from the stone's interior. In the case of chert, quartz or quartzite, this alteration is basically mechanical, and apart from the colour and the wear it has the same characteristics as the interior in terms of hardness, toughness etc. However, flint is surrounded by a limestone cortex that is soft and unsuitable for stone tools. As hand axes are made from a tool stone's core, it is normal to indicate the thickness and position of the cortex in order to better understand the techniques that are required in their manufacture. The variation in cortex between utensils should not be taken as an indication of their age.
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