Unglazed tile, usually 6 in. 2 or more in surface area and ‘/2 to 3/4 in (13 to 19 mm) in thickness made by the extrusion process from natural clay or shales.

A hard, dense tile of homogeneous composition throughout, deriving color and texture from the materials of which the body is made. The colors and characteristics of the tile are determined by the materials used in the body, the method of manufacture, and the thermal treatment.