Surface roughness on lapped work is usually interpreted as the result of the generation of chips. It is desirable to convert the extra energy, supplied to make chips, into heat energy to be removed with the chips. However, such energy is actually kept in the lapped surface in the form of strain, stress, and damaged layers. No divergence occurs in the relation between chip generation and surface toughness. In lapping hard and brittle materials such as glass, the presence of plastic deformation on a top surface layer, microcrack toward the inside, and plastic and elastic deformations at the extension of such cracks have been detected. These issues have been clarified by lapping single crystals such as quartz and silicon. [12] and [14]