A composition with a Mohs hardness of at least 6.0, wherein said composition contains at least 30 weight percent of spinel crystals, at least 10 weight percent of glass, and less than 10 weight percent of ferrometalsilicate. The composition also contains particles with a particle size distribution such that at least about 95 weight percent of such particles are smaller than about 2.0 millimeters; at least about 70 weight percent of such particles have a particle shape that is either the blocky particle shape or the pyramidal particle shape. At least 20 weight percent of the spinel crystals are equiaxed spinel crystals; the weight/weight ratio of said spinel crystals to said glass is at least 1.2/1; the composition has a melting point in excess of 1440 degrees Celsius; and the composition has a density of from about 3.0 to about 4.5.