Sandstone changes into quartzite through the pressure and heating that results from tectonic compression inside the orogenic belts. The sandstone transforms into quartzite gradually and with little change at a mineralogic level.
When the transition from sandstone to quartzite occurs, the quartz grains in the sandstone recrystallize and form sedimentary structures of quartz crystals. Quartzite is a hard metamorphic rock that is usually gray or white, but may take other light colors depending on the impurities present in the sandstone. This rock occurs often in areas with high-pressure metamorphism. Examples of regions with quartzite quarries in the United States include Idaho, Wisconsin, New York, Minnesota, Pennsylvania, Arizona, Montana and South Dakota. The rock is resistant to chemical weathering, and its almost pure silica content leads to little to no vegetation on quartzite ridges.