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Formation and Composition
Quartzite is a metamorphic rock made from quartz sandstone, pressed together over millions of years. Most quartzite contains 90 percent or more quartz. It comes in a wide variety of colors, from green to pink to black. Sometimes, a large outcropping of quartzite maintains the layers found in the original sandstone. Other times, the layers have been mixed during metamorphosis and it has a speckled appearance. Often, you can see remains of small sand grains or pebbles in the rock.
Identification
Because quartzite comes in such a wide variety of colors, it can be difficult to identify. To find out if your rock is quartzite, break it. In quartzite, the rock will break across grains, producing a relatively smooth surface. In quartz sandstone, it will break around quartz grains, making a rough, grainy surface. Another way to identify quartzite is by conducting a hardness test. Quartzite is harder than a steel nail; it will leave a mark on the nail when scratched against it.
Uses
Quartzite is a common landscaping rock, usually appearing white or pink and sometimes slightly transparent. It is also used in building construction for roofing, flooring and wall coverings. It can be polished smooth to become a bathroom or kitchen countertop, with an appearance similar to granite. It is used as a gemstone in jewelry as well.
Locations
Quartzite can be found almost anywhere in the world. Because it weathers very slowly, large outcroppings can be found in many mountainous areas. There is a reddish deposit near Almeria, Sierra de Gador, Spain. A green deposit exists in the state of Mysore, India. A type of quartzite called Greenlandite has a blue-green color. In the U.S., there are large outcroppings found in the Appalachian Mountains. Other deposits in the U.S. are located in southwest Minnesota, the mountains of Arizona and Southern California and in Devil's Lake State Park in Wisconsin.
History
Throughout history, quartzite has been used as a gemrock for beads and jewelry. It has often been used as a substitute for jade. "Indian jade" is actually quartzite with fuchsite inclusions. Greenlandite has been called the world's oldest gemstone. Quartzite was also used as money in West Africa from the 17th century onward. Africans took 2-inch diameter quartz stones and drilled holes in both sides. Some statues are made of quartzite as well, such as the head of King Amenhotep III, which was carved from brown and white quartzite.