>99% quartz sand. A coarse, rounded-grain refractory used on kiln shelves to ease shrinkage movement of large pieces or, in limited amounts, as a grog in sculpture clay bodies. 

Grain size: 1% retained on 30 mesh; 52% on 40m; 41% on 50m; 5% on 70m; 1% on 100m.

For more information on silica sand, see the Digitalfire.com Reference Library of ceramic materials.