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Minerals Found in Skarn
Skarns often contain a diverse assemblage of metamorphic minerals. The mineral assemblage in a skarn is determined by the lithology of the invaded rock, the chemistry of the invading liquid, and the temperature of the rock environment. Metamorphic minerals that characterize the skarn environment include a wide range of calc-silicates, many types of garnet, and a…
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Other Skarn Environments
In the example described above, skarn formed in a carbonate rock unit adjacent to a magma intrusion. There are numerous other geological situations where skarn can be formed. These include: Skarn can form with various water inputs. These include include:
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Skarn as a Complex Rock Mass
Skarns can form on both sides of the boundary between a magma body and its surrounding rock mass. Those formed on the igneous side of the contact are known as endoskarns. Those formed on the country-rock side of the contact are known as exoskarns. Exoskarns form when the original chemistry of a rock mass is altered –…
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An Example of Skarn Formation
Most skarns form when carbonate rocks such as limestone, dolostone, or marble are intruded by a magma body and altered by contact metamorphism and metasomatism. At the time of intrusion, the heat of contact metamorphism is the primary agent of change. Then, as the magma cools, it releases hot, acidic, silicate-rich fluids. Some magmas contain up to several percent…
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What is Skarn?
Skarn is a metamorphic rock that has been chemically and mineralogically altered by metasomatism. Metasomatism is the alteration of rocks by hot, chemically-active fluids that flow or diffuse through the rocks and cause recrystallization and compositional change. Skarn commonly forms around the edges of a magma body that intrudes a nearby rock mass. Rocks formed or altered by the interaction…
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Schist As a Gem Material Host Rock
Schist is often the host rock for a variety of gemstones that form in metamorphic rocks. Gem-quality garnet, kyanite, tanzanite, emerald, andalusite, sphene, sapphire, ruby, scapolite, iolite, chrysoberyl and many other gem materials are found in schist. Gem materials found in schist are often highly included. This is because their mineral crystals grow within the rock matrix, often including mineral grains of the host rock instead of replacing them or…
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Schist As a Construction Material
Schist is not a rock with numerous industrial uses. Its abundant mica grains and its schistosity make it a rock of low physical strength, usually unsuitable for use as a construction aggregate, building stone, or decorative stone. The only exception is for its use as a fill when the physical properties of the material are not…
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Types of Schist and Their Composition
As explained above, mica minerals such as chlorite, muscovite, and biotite are the characteristic minerals of schist. These were formed through metamorphism of the clay minerals present in the protolith. Other common minerals in schist include quartz and feldspars that are inherited from the protolith. Micas, feldspars, and quartz usually account for most of the minerals present in a…
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How Does Schist Form?
Schist is a rock that has been exposed to a moderate level of heat and a moderate level of pressure. Let’s trace its formation from its protoliths – the sedimentary rocks from which it forms. These are usually shales or mudstones. In the convergent plate boundary environment, heat and chemical activity transform the clay minerals…
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What is Schist?
Schist is a foliated metamorphic rock made up of plate-shaped mineral grains that are large enough to see with an unaided eye. It usually forms on a continental side of a convergent plate boundary where sedimentary rocks, such as shales and mudstones, have been subjected to compressive forces, heat, and chemical activity. This metamorphic environment is intense enough to convert the clay minerals…