Fired ceramic has the potential of being extremely hard and resistant to abrasion and wear. Special abrasion resistant ceramic products are made from highly specialized materials and fired to exacting requirements. Calcined alumina, for example, can be cast and fired to very high temperatures to produce surfaces with exceptional resistance to abrasion. Likewise, aggregates and bonding frits are employed by the abrasives industry to make all kinds of abrasive products (products designed to abrade others). The hardness of pottery is mainly dependent on the development of aluminum silicates during firing (i.e. mullite crystals). This requires temperatures high enough to melt fluxes to allow them to dissolve quartz and other minerals. It also requires time to allow these processes to complete. Likewise the glaze components most resistant to abrasion are refractory alumina and silica, and the higher you fire the more you can get into your glaze and yet still get it to melt.