Quartzite is a widely available, hard, cheap, and durable non-foliated metamorphic rock. The rock is economically important because it has tons of uses.
The word quartzite is derived from the German word “quartzit.” One interesting thing about “quartzite” is that it is often used for hard but non-metamorphosed sandstones. These rocks are known as orthoquartzite to differentiate them from metamorphic quartzite. Metamorphic quartzite is also known as metaquartzite to elaborate on its metamorphic nature.
Quartzite is also a ridge-former because it is one of the earth’s most durable and chemical-resistant rocks. When erosion and weathering take down mountain ranges, quartzite stands tall against these events and forms ridges when less durable and less-resistant rocks are grounded. You will often see quartzite at the crest of mountain ranges.
Quartzite rock is named quartzite because of its quartz content in it. Most specimens contain up to 90% percent quartz. Some specimens may also contain up to 99% quartz. These quartzite rocks are said to be the largest and purest silica reserves on earth.
British Geological Survey states that a metamorphic rock must have 80% quartz by volume to be classified as quartzite.
Quartzite usually has a sugary appearance and a glassy shine. Colored quartzite is also common. The rock gets different and interesting colors due to trace amounts of impurities. Pure quartzite is usually white to grey. It takes red/pink shades due to hematite presence. Other minerals may impart yellow, green, blue, or orange colors.
Quartzite looks similar to marble, but it is more durable than marble. It isn’t scratched by a metal blade and doesn’t fizz or discolor when it comes in contact with acidic solutions.
Quartz-rich sandstone may look similar to quartzite. One major difference is how both rocks show breakage. Quartzite shows breakage across the quartz grains, and sandstone breaks around quartz grains.
Due to its strong interlocking grains, quartzite is a durable, tough, and hard rock. Quartzite is usually white, but impurities can give it different colors. It has a rating of 7 on the Mohs hardness scale, showing that it belongs to one of the hardest rocks.
These properties make it a perfect rock for cutting tools like ax heads and scrapers. It has a coarser texture and is not used to make fine-edged tools.
The rock formation process takes place during mountain-building events at convergent plate boundaries. Quartzite forms when quartz-rich sandstone (a sedimentary rock) is changed by metamorphism. The heat, pressure, and chemical activity are applied to recrystallize the sand grains and silica cement. The resultant rock formed is a powerhouse of strength and durability. The interlocking quartz grain provides unmatchable strength to the rock, which increases its commercial value.
The sedimentary structure and original texture of the rocks are erased during metamorphism. The resultant quartz grains are almost the same in size with a more multi-sided texture. The grains are so firmly held together that when the rock is broken, it cracks through the grains to form a conchoidal fracture.
Where is Quartzite Found?
- Quartzite is a commonly found and highly-sought after rock due to its multiple uses. Large reserves are located in North America.
- Quartzite formations can be found in Pennsylvania, Texas, Washington DC, Central Texas, Eastern South Dakota, Southwest Minnesota, Wisconsin, Utah, and Arizona.
- The La Cloche Mountains in Ontario, Canada, are made of white quartzite. Huge quartzite reserves are also located in Nova Scotia.
- United Kingdom, Ireland, and the Czech Republic, also have notable reserves.
Quartzite is a commercially valuable rock. Its main uses are outlined below.
- Quartzite is durable and chemically resistant rock. It can withstand weathering events better than marble and granite. Hence, it is used in stair steps, floor tiles, countertops, and outdoor uses.
- It is crushed for construction projects. Since it is an extremely hard rock, it damages the crushing machinery, limiting its constructional use.
- Some quartzite mines have up to 98% silica content. These are used to manufacture glass, silicon metal, and silicon carbide.
- The presence of impurities gives the rock a colored look. It is used as a decorative rock, collectible, and interior design.
- Ancient civilizations used quartzite to make stone tools like axe heads and other cutting tools.