AL Stone is composed of pure synthetic alumina mainly which is made by chemical synthesis and AI₂ O₃, Cr, Na₂ O₃, MgO, etc. are combined. These materials are heated at high temperatures (1,600˚C – 1,700˚C) to be hardened fused crystals (d-AI₂O₃). Comparatively, the specific gravity of AL Stone (3.0 – 3.6) is rather heavy among barrel stones which property shows excellent grinding efficiency. AL Stone is a stable all-round stone and of wide application from heavy jobs to finishing. Since the hardness is very hard, AL Stone is the most suitable for high-speed barrel grinding.