What is Quartzite?
Quartzite is a non-foliated metamorphic rock that occurs when quartz enriched sandstone or chert is changed by the high temperature, pressure, and chemical activity of the metamorphism. These cause the quartz grains to infuse together to shape a dense, hard, equigranular (consisting of minerals of approximately the same size) rock. Quartzite rock is usually made up of more than 90% quartz; some specimens even consist of 99% quartz.
The biggest and purest concentration of silica on the earth's surface, Quartzite implies not only a high concentration of quartz but also a high degree of induration (hardness). Quartzite rock may look similar to quartz-rich sandstone, but the former has a glossy sheen.
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The intertwining crystalline structure of the rock makes it solid, hard, and durable. Quartzite is so hard that breakage occurs across quartz grains rather than breaking along boundaries between them. This unique feature separates quartzite rock from quartz enriched sandstone. Quartzite is generally white to gray in colour, but some with iron contents may appear pink. Some other trace minerals incorporated in quartz during metamorphism can make quartzite appear yellow, green, brown, blue, or orange. Apparently, quartzite may look the same as marble, but a metal blade cannot scrape a quartzite, and it will not exhibit effervescence with contact with dilute hydrochloric acid.
Quartzite Meaning
Quartzite is an extremely compact, hard granular rock primarily made of quartz. The high concentration of quartz in quartzite gives it a hardness of about seven on the Mohs Hardness Scale. The most crucial test to identify the mineral contents is the Mohs Hardness Test. The test is to check the comparative resistance of minerals being scuffed with ten minerals known as Mohs Hardness Scale, chronologically talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, and diamond. Its conchoidal fracture permits it to be curved into large cutting tools such as ax heads and scrapers. Due to its course structure, it is unfavorable to produce sharp edges like knife blades and shell points. Quartzite means metamorphosed sandstone.
Two forms of metamorphism create quartzite; contact and Barrovian. When molten magma gushes out and comes in contact with sandstone, it gets scorched and fuses so forcefully that it loses its inherent structure. The minerals crystallize firmly to produce quartzite. The deeper and hotter the sandstone gets, it blends more strongly.
Seafloor spreading occurs due to tectonic activities, which give rise to huge mountains. The massive forceful tectonic collisions produce extreme compression forces that consequently push, crush and squeeze sandstones. During these extreme exterior forces, sandstone metamorphoses into quartz, feldspar, amphibole, and biotite. Major physical changes occur during metamorphosis as all or most sedimentary properties, texture, and structure of sandstone undergo change. The super grain sand-paper-like exterior of sandstone turns into a glossy sheen. During this crystallization, former binding minerals like iron oxide, silica, clay, and carbonate migrate. These are considered impurities in quartzite rock and the reason for black quartzite, green, brown, or blue quartzite. Veining pattern in quartzite is also formed due to this process. Since the transition of sandstone to quartzite is gradual, some geologists suggest an intermediate rock called quartz arenite.
Quartzite Uses
Since quartzite is extremely durable and chemical and heat resistant, it is used as quartzite countertops in the kitchen; as quartzite is a decorative stone with varying colors and vein patterns, it is used in wall tiles, roof tiles, and also in flooring and staircase. Unlike sandstone, quartzite has a varying level of porosity depending on the porosity of the parent rock. Pure quartzites are used as a source of silica for metallurgical purposes and to manufacture silica bricks. Quartzites are also mined to paving blocks, riprap, railroad ballast, rod metal (crushed stone), and roofing granules.
Difference Between Quartz and Quartzite
The word quartz is used to describe various materials, ranging from a mineral consisting of silica and oxygen atoms to engineered stone material used to craft kitchen countertops. The latter is also referred to as quartz due to its predominant constitution. The quartz kitchen countertops contain a lot of mineral quartz mixed with a polymer resin (less than 10% of the weight), hence called quartz.
Quartzite is a metamorphic rock, while quartz is an igneous rock that crystallizes from magma or precipitates from hydrothermal vents of mid-ocean ridges. Sandstone metamorphoses under extreme heat, pressure, and chemical reaction from quartz arenite and quartzite. Quartzite is a metamorphic rock mainly consisting of quartz (more than 90%). Other minerals are feldspar, mica, magnetite, zircon, and rutile.
FAQs on Quartzite
1. What is quartzite and how is it formed?
Quartzite is a hard, non-foliated metamorphic rock. It is formed when its parent rock, pure quartz sandstone, is subjected to intense heat and pressure deep within the Earth's crust. This process, called metamorphism, causes the individual quartz sand grains and the silica cement holding them together to recrystallize and fuse into a dense, interlocking mosaic of quartz crystals.
2. What are the main physical and chemical characteristics of quartzite?
Quartzite is known for its distinct characteristics which make it a very durable rock. Key properties include:
- Hardness: It is extremely hard, rating about 7 on the Mohs scale, which means it can scratch glass and steel.
- Durability: Due to its interlocking crystalline structure, it is highly resistant to physical weathering and erosion.
- Chemical Resistance: Composed mainly of silicon dioxide (SiO₂), it is chemically stable and does not react with common acids like hydrochloric acid.
- Texture: It has a granular, sandpaper-like texture and a glassy lustre on fresh surfaces.
- Low Porosity: The metamorphic process makes most quartzites very dense with low porosity, meaning they do not absorb water easily.
3. What are the most common uses of quartzite?
Due to its hardness and durability, quartzite has several important applications. Common uses include as a decorative stone for kitchen countertops, flooring, and wall tiles. In construction, it is crushed and used as railway ballast and road aggregate. Because of its high silica content, it is also used in the manufacturing of silica bricks and other refractory materials needed for high-temperature applications.
4. What is the main difference between quartz and quartzite?
The primary difference is that quartz is a single mineral, a natural compound of silicon and oxygen (SiO₂), often found as individual crystals. In contrast, quartzite is a rock, specifically a metamorphic rock, that is composed almost entirely of these quartz mineral crystals fused together. In simple terms, quartz is the ingredient, while quartzite is the finished product created by nature's heat and pressure.
5. How does quartzite's formation process make it different from its parent rock, sandstone?
While both are composed of quartz, their structures are very different. Sandstone is a sedimentary rock where individual sand grains are held together by a mineral cement. If it breaks, the fracture occurs around the grains. In quartzite, the intense metamorphism has recrystallized both the grains and the cement into a single, interlocking mass. This means a fracture will cut right through the quartz grains, not around them, making quartzite significantly stronger and more durable than sandstone.
6. Why is quartzite classified as a non-foliated metamorphic rock?
Quartzite is classified as non-foliated because its mineral grains are not aligned in parallel layers or bands. Foliation typically occurs when platy or elongated minerals (like mica) align themselves under directional pressure. Since quartzite is predominantly made of granular quartz crystals which are roughly equal in all dimensions, they do not align into layers when compressed. Instead, they fuse together, creating a massive, granular texture.
7. What factors determine the different colours found in quartzite?
Pure quartzite is typically white to grey. However, it can appear in various colours due to mineral impurities present in the original sandstone. For example:
- Iron oxides (hematite) can give it pink or red hues.
- Minerals like fuchsite or serpentine can impart a green colour.
- Other impurities can result in shades of yellow, blue, brown, or orange.
8. How does the hardness of quartzite compare to other common stones like marble and granite?
Quartzite is significantly harder than many other common stones. On the Mohs hardness scale:
- Quartzite ranks at about 7.
- Granite, another hard rock, typically ranks between 6 and 7.
- Marble is much softer, ranking only at 3 to 4.
This superior hardness means quartzite is highly resistant to scratching, making it a more durable choice for surfaces like countertops compared to marble.
9. Since quartzite originates from sandstone, is it possible for it to contain fossils?
It is extremely unlikely. The intense heat and pressure involved in the metamorphism of sandstone into quartzite typically destroys any original sedimentary structures, including any fossils that may have been present. The process of recrystallization completely alters the rock's original fabric, effectively erasing any fossil evidence. Therefore, for all practical purposes, quartzite is considered a fossil-free rock.
10. Where can major deposits of quartzite be found in India?
In India, quartzite is a common rock found in various geological formations. Significant deposits are located in the ancient mountain ranges, particularly the Aravalli Range in Rajasthan. It is also extensively found in states like Andhra Pradesh, Madhya Pradesh, Odisha, and across the Himalayan region, where it forms prominent ridges and peaks due to its resistance to weathering.
