Quartzite, common and widely distributed rock composed mainly or entirely of quartz. The compact, granular rock is a form of metamorphosed sandstone in which silica, or quartz, has been deposited between the grains of quartz of which the sandstone is essentially composed. Other minerals that may be present in small amounts in quartzite include feldspar, mica, rutile, tourmaline, and zircon. Quartzite has a smooth fracture and is found primarily among ancient rocks, such as those of the Cambrian or Precambrian system.
