There are many different types of rock used as aggregate. Generally, hard aggregate breaks down the cutting diamonds faster which means the bond must be softer to expose new diamonds. Softer aggregate generally does not break down the cutting diamond as quickly and therefore requires a harder bond to hold the diamonds in place to use their full potential. The Mohs’ scale is used to measure the hardness of aggregate and has a range of 1 – 10. Most aggregates fall into the 2 – 9 range.