Typical hard rock sources of aggregate for concrete are from Greywacke and Basalt quarries. The hardness of these rocks makes the generation of fines in the 1.18mm to 0.3mm size range difficult. In harder materials the mechanical creation of fines in this particle range is difficult with typical crushing equipment. Therefore standard practice is to use manufactured sand from an VSI Impact Crusher and to supplement this with a small percentage of natural sand and in some cases fine marine sand. The resulting blended sand is less harsh and offers better field performance.