In analyzing the functions of prehistoric stone tools and employing use-wear techniques, considerable emphasis has been placed on scar type and patterning. Variables of scarring may be better understood with reference to the mechanics of fracture to brittle solids. This article examines damage characteristic of tool use on raw materials of various degrees of relative hardness and in 10 different motor activities. The author proposes hypotheses to account for the various types of micro-fracture in these different situations.