Modern tumbling media is made by high temperature firing of ceramics containing crushed silica, and usually has a hardness of at least 7 on the Mohs scale (but can be tailored to lower hardness if required/desired). However, for high tech applications the hardness can be raised further by the inclusion of other (usually man-made) grits. Silicon carbide is frequently used and that has a hardness of about 9.5 (versus corundum at 9.0)