Term: Quartzite
**Characteristics and Origin**:
– Quartzite is a hard rock with an interlocking mosaic of quartz crystals.
– The surface of quartzite is grainy and glassy in appearance.
– Quartzite must contain at least 80% quartz by volume for British Geological Survey classification.
– Quartzite is formed when sandstone undergoes regional metamorphism, with quartz grains recrystallizing.
– Recrystallized quartz grains in quartzite are roughly equal in size, forming a granoblastic texture.
**Geographical Occurrence**:
– Quartzite formations can be found in regions across the United States, including Pennsylvania, South Dakota, and Utah.
– Notable locations with quartzite include the Morenci Copper Mine in Arizona and the La Cloche Mountains in Ontario, Canada.
– Quartzite deposits are also present in Ireland, the United Kingdom, and continental Europe.
– Precambrian basement rock in western North America features Paleoproterozoic quartzite-rhyolite successions.
**Uses**:
– Quartzite has historical uses in prehistoric stone tools and contemporary applications as decorative dimension stone.
– It is utilized in highway construction as crushed stone and as a source of silica for silicon production.
– Quartzite’s hardness and resistance make it valuable for various industrial applications.
– Increasingly used for kitchen countertops due to its durability and stain resistance.
**Relationships with Other Rocks**:
– Quartzite is derived from the metamorphism of quartz sandstone.
– Orthoquartzite and metaquartzite describe different levels of cementation and metamorphism in quartzite.
– The distinction between orthoquartzite and quartz sandstone lies in the cementation level.
– As metamorphism progresses, quartz grains in quartzite undergo recrystallization, leading to different textures.
**Safety and Etymology**:
– Quartzite, being a form of silica, poses risks in workplaces due to hazardous silica dust.
– Activities like cutting, grinding, and polishing quartzite can release respirable crystalline silica.
– Workers involved in quartzite processing should take precautions to minimize exposure to silica dust.
– The term ‘quartzite’ originates from the German word ‘Quarzit’.
Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite. Other colors, such as yellow, green, blue and orange, are due to other minerals.
| Metamorphic rock | |
 Quartzite, containing darker bands of phengite and chlorite, from Maurienne Valley in the French Alps | |
| Composition | |
|---|---|
| Quartz | |
| Physical Characteristics | |
| Fabric | Non-foliated |
| Relationships | |
| Protoliths | Quartz Sandstone |
The term quartzite is also sometimes used for very hard but unmetamorphosed sandstones that are composed of quartz grains thoroughly cemented with additional quartz. Such sedimentary rock has come to be described as orthoquartzite to distinguish it from metamorphic quartzite, which is sometimes called metaquartzite to emphasize its metamorphic origins.
Quartzite is very resistant to chemical weathering and often forms ridges and resistant hilltops. The nearly pure silica content of the rock provides little material for soil; therefore, the quartzite ridges are often bare or covered only with a very thin layer of soil and little (if any) vegetation. Some quartzites contain just enough weather-susceptible nutrient-bearing minerals such as carbonates and chlorite to form a loamy, fairly fertile though shallow and stony soil.
Quartzite has been used since prehistoric times for stone tools. It is presently used for decorative dimension stone, as crushed stone in highway construction, and as a source of silica for production of silicon and silicon compounds.