21232  Sand, Gravel, Clay, and Ceramic and Refractory Minerals
Mining and Quarrying 

This industry comprises (1) establishments primarily engaged in
developing the mine site and/or mining, quarrying, dredging for sand
and gravel, or mining clay, (e.g., china clay, paper clay and slip
clay) and (2) preparation plants primarily engaged in beneficiating
(e.g., washing, screening, and grinding) sand and gravel, clay, and
ceramic and refractory minerals.