Specific tests used to determine the suitability of aggregates for special purposes. There are tests for: (a) shape and texture (the angularity number), to determine whether particles have a large angle of friction with good bonding properties; (b) size and grading, to determine whether particles will pack well; (c) moisture content, to discover whether materials absorb so much water that freeze–thaw action might cause the break-up of structures; (d) rock density, which may affect the economics of an operation; (e) strength, determined by subjecting the rock to hammering in a standard test and measuring the percentage of fine material produced (the aggregate impact value, or AIV); (f) resistance to crushing (the aggregate crushing value, or ACV), measured in a similar manner; (g) resistance to abrasion, measured by standard equipment to give the aggregate abrasion value (AAV)—the lower the AAV, the more resistant the rock; and (h) resistance to polishing, measured in the laboratory to give the polished stone value (PSV)—the higher the PSV, the greater the resistance to polishing and therefore skidding, and the more valuable the material.