Quartzite is a non-foliated metamorphic rock formed from sandstone and is primarily made up of quartz. Non-foliated means that quartzite does not display the banding and layers of other kinds of metamorphic rocks like slate or schist. When cut, the break will slice through the grains and not around them.
• How quartzite is formed
Quartzite is formed from quartz sandstone which is a sedimentary rock. High temperatures and pressure cause the metamorphosis of sandstone into quartzite. Typically, quartzite is formed in regions of high-pressure mountain-building events where continents collide. It can be found all over the world from Brazil to the United Kingdom. In the United States, quartzite is quarried in Arizona, Idaho, Minnesota, Montana, New York, Pennsylvania, South Dakota and Wisconsin. The town of Quartzite, Arizona is famous for its rich supply of the mineral and hosts rock shows and fairs for tourists. Quartzite deposits can be found in many more states such as Vermont and Utah. Many outcroppings and ridges in the Appalachians are composed of quartzite. Another form of quartzite, quartz arenites may be formed by precipitation of silica in underground water sources.
• Composition
Quartzite is composed of 90 to 99% quartz crystals. When metamorphism occurs, the quartz grains recrystallize and become tightly interwoven, or cemented. For this reason, when quartzite is broken, the break goes clean through the individual sand grains instead of around them as it does in sandstone. This leaves a smooth surface after a break, rather than a bumpy one. Small amounts of silica, iron oxide, clay and carbonate may be present and will cause a streaked appearance.
• Color
Quartzite is usually white, gray, light brown or yellow, but trace minerals such as iron oxide can give it a pinkish hue. Other trace minerals can cause more variations in colors, sometimes producing black, blue, green or purple. It has a glassy luster.
• Uses
Quartzite is a very hard, durable rock. It is used in the manufacture of glass and ceramics. In construction, quartzite can be used for countertops, fireplaces and flooring. Because it has a smooth surface when cut, quartzite slabs can be used for walls. Because of its durability and appearance, quartzite is becoming popular for decorating homes and may be used to create bricks and decorative tiles. Crushed quartzite is used for gravel, and in building roads. It is also used for railroad ballast, where it is placed under and around train tracks to provide stability, water drainage and to keep weeds from sprouting along the track.
