Quartzites are metamorphosed sedimentary quartz sandstones. Deep in the earth, rocks are heated by molten. Pressure comes from layer upon layer of rocks. Heat and pressure may cause chemical changes within the parent rock. The parent rock, sandstone, now becomes a different rock, quartzite. Erosion and uplifting eventually bring the quartzite to the earth’s crust. This is the process of metamorphosis.
A quartzite is a granular rock, meaning that it is uniform in composition. Granular rocks are all one mineral; quartzite’s uniform composition is quartz. Quartz is one of the most abundant rock-forming minerals. Approximately 12% if the earth’s crust is quartz. Quartzite is a non-foliated rock lacking banding or layers. Quartzite is far harder than its parent rock, sandstone.
The quartz grains within the quartzite are deformed, locked and fused together. When quartzite breaks, it usually breaks through the grains.
Quartzite, which has not been exposed to weather, looks like sugar has been used as a coating on the rock. The color of quartzite is gray or white. However, iron oxide, feldspar, or zircons are impurities that can be found in quartzite making yellow, red, and orange quartzite. Orthoquartzite is the purest form of quartzite is made of 99% silicon oxide, which makes it pure quartz.
Quartzite can be found in Greenland, Turkey, Spain, India and Brazil. In the United States quartzite can be found in the Appalachian Mountain ridges, Palisades State Park in South Dakota (there are 50 foot quartzite cliffs there), Death Valley National Park (near San Bernardino, CA) and in Quartzite, Arizona. Quartzite can be seen at Storm Mountain in Big Cottonwood Canyon in Salt Lake County, and in some areas of Idaho.
Crushed quartzite is used for railroad ballast because of its hardness and angular shape. Crushed quartzite can also be used in road construction. Quartzite is considered a decorative stone and can be used as flooring, in roofing tiles, wall coverings, and for stairs. Quartzite sand is used for septic tank covers and golf course bunkers. Dyed quartzite rocks are used to make jewelry and paperweights. Quartzite used for building stone is quarried from the Raft River and the Grouse Mountains. There is quartzite from Idaho that is so pure, that it can be used to make into computer chips.
In conclusion, quartzite is a metamorphic rock that metamorphosed from sandstone through heat and pressure in a process that took millions of years. Quartzite is a granular rock composed of quartz crystals. Quartzite is valued for its strength and is most often used as railroad ballast and in road construction.