Camel CGW brand grinding abrasive blades for angle grinders are made from bonded abrasive minerals with varying hardness properties allowing for the production of myriad grinding characteristics.  The most common mineral used is Aluminum Oxide.  Zirconia with Aluminum Oxide grain mix also used for the "ZA" series which yields higher performance cutting for high tensile, hardened or high speed steels. Alumimun Oxide does a good job on lower tensile steels, ductile and non-ferrous metals.