Abrasives are used to improve machinability in the abrasive water jet. We and many water jets use garnet as an abrasive. It is a natural stone mainly composed of garnet SiO4 and has a hardness (Mohs) of 6.5 to 7.5. It is often used as a file because it is relatively inexpensive among high-hardness minerals.
As a weak point, diamonds with a hardness higher than garnet, such as diamond with Mohs hardness 10 and high-purity SiC with hardness 9 cannot be cut in principle.
