Quartzite is a metamorphic rock formed when quartz-rich sandstone or chert has been exposed to high temperatures and pressures. The name quartzite implies not only a high degree of induration (hardness), but also a high quartz content. Quartzite generally comprises greater than 90% percent quartz, and some examples, containing up to 99% quartz, are the largest and purest concentrations of silica in the Earths crust. Although a quartz-rich sandstone can look similar to quartzite, a fresh broken surface of quartzite will show breakage across quartz grains, whereas the sandstone will break around quartz grains. Quartzite also tends to have a sugary appearance and glassy lustre. The variety of colors displayed by quartzite are a consequence of minor amounts of impurities being incorporated with the quartz during metamorphism.

In summary, quartzite is a very hard, non-foliated, medium to coarsely crystalline, and almost mono mineral metamorphic rock with granoblastic texture. It is composed almost entirely of quartz and is formed when quartz-rich sandstone or chert is exposed to high temperatures and pressures.