Quartz sand has a high resistance to being crushed. In the petroleum industry, sand slurries are forced down oil and gas wells under very high pressures in a process known as hydraulic fracturing. This high pressure fractures the reservoir rocks, and the sandy slurry injects into the fractures. Quartz is one of the most useful natural materials. Its usefulness can be linked to its physical and chemical properties, Glass Making, The high hardness of quartz, seven on the large Scale, makes it harder than most other natural substances. As such it is an excellent abrasive material. Quartz is very resistant to both chemicals and heat. It is therefore often used as a foundry sand. With a melting temperature higher than most metals.