A metamorphic rock consisting largely or entirely of quartz. Most quartzites are formed by metamorphism of sandstone; but some have developed by metasomatic introduction of quartz, SiO₂, often accompanied by other chemical elements, for example, metals and sulphur (ore quartzites). The geological relations and the shape of quartzite bodies serve to distinguish between them (see illus.). The metasomatic quartzites are often found as contact products of intrusive bodies.