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Serpentinite

earth science Maturity 7-9 Next article →

Serpentinite is a metamorphic rock that forms through a specific chemical process. It is composed mostly of minerals from the serpentine group.

Serpentinite
Serpentinite

This rock is significant because its formation can influence the chemistry of the ocean and the crust. It is also famous for its unique appearance. The name might come from its resemblance to snake skin.

Serpentinite
Serpentinite

In ancient times, a Greek pharmacologist named Dioscorides suggested using it to prevent snakebites. Today, it is recognized for its role in geology and its use in various human industries.

The formation of serpentinite occurs through a process called serpentinization. This happens when mafic or ultramafic rocks are hydrated by seawater. This seawater must be deficient in carbon dioxide. The water is pressed into the rock at great depths below the ocean floor.

Gros Morne moho
Gros Morne moho

This process typically occurs at mid-ocean ridges or in the forearc mantle of subduction zones. As the water reacts with the rock, the original minerals transform. The final composition is usually dominated by serpentine subgroup minerals. These include antigorite, lizardite, and chrysotile. Magnetite is also a common component, while brucite may appear less frequently.

Serpentinization does more than just change the rock's appearance. It also triggers chemical reactions that produce molecular hydrogen. One specific reaction involves the transformation of fayalite into magnetite and quartz. This reaction produces hydrogen gas as a result. This process is similar to the Schikorr reaction. In that reaction, iron ions are oxidized by protons from water. The hydrogen produced is very important for deep-sea environments. It can serve as a fuel source for microbial activity in the deep subsurface.

Expl2224 - Flickr - NOAA Photo Library
Expl2224 - Flickr - NOAA Photo Library

These chemical processes create unique environments like hydrothermal vents. Some vents, such as those in the Rainbow field of the Mid-Atlantic Ridge, emit complex hydrocarbon molecules. Other sites, like the Lost City Hydrothermal Field, may be driven by the heat of serpentinization itself. These vents are different from typical "black smokers." They emit relatively cool, highly alkaline fluids that are high in magnesium. These fluids are low in hydrogen sulfide. The vents can build massive carbonate and brucite chimneys. These structures can reach heights of up to 60 meters. These sites host lush microbial communities.

Because of these chemical properties, scientists consider serpentinite vents a candidate for the origin of life. Many chemical reactions needed to synthesize acetyl-CoA happen during serpentinization. Acetyl-CoA is essential to the basic biochemical pathways of all life. Additionally, the sulfide-metal clusters that activate many enzymes look like the sulfide minerals formed during this process. This connection suggests that the early Earth might have supported life through these hydrothermal systems. The rock acts as a chemical engine that drives these complex biological possibilities.

Serpentinite also creates very specific ecosystems on land. The soil covering serpentinite bedrock is often thin or completely absent. This soil is poor in calcium and other major plant nutrients. However, it is rich in elements that are toxic to many plants, such as nickel and chromium.

Landscape, south of New Caledonia
Landscape, south of New Caledonia

Because of this, only certain species have adapted to live there. Plants like Clarkia franciscana and some manzanita species thrive on these outcrops. Because these outcrops are often small and isolated, they act as ecological islands. This makes the plants living there highly endangered. In New Caledonia, these specialized plant communities are able to resist invasive species.

Humans have used serpentinite for many different purposes throughout history. It has a Mohs hardness of 2.5 to 3.5, which makes it easy to carve.

Zwei trinkbecher, zoeblitz
Zwei trinkbecher, zoeblitz

Historically, it has been used as a decorative stone in architecture. College Hall at the University of Pennsylvania is a notable example of a building made of serpentine. The Inuit people used it to carve lamps called qulliq to burn oil for heat and light. In modern technology, serpentinite has a very specialized role. Because it contains much bound water, it can slow down neutrons in nuclear reactors. It is used as a filler in steel jackets or as an additive in special concrete to increase density and neutron capture. It may also help with carbon dioxide sequestration by absorbing CO2 from the atmosphere.

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🖼️ Images & Media (9)
File:Serpentinite sur gneiss.jpg
Serpentinite sur gneiss.jpg
File:Serpentinite.JPG
Serpentinite.JPG
File:Chromitic serpentinite Styria Province, Austria.jpg
Chromitic serpentinite Styria Province,...
File:Folded serpentinite.jpg
Folded serpentinite.jpg
File:Gros Morne moho.jpg
Gros Morne moho.jpg
File:Expl2224 - Flickr - NOAA Photo Library.jpg
Expl2224 - Flickr - NOAA Photo Library.jpg
File:Landscape, south of New Caledonia.jpg
Landscape, south of New Caledonia.jpg
File:Zwei trinkbecher, zoeblitz.jpg
Zwei trinkbecher, zoeblitz.jpg
File:College Hall U Penn.JPG
College Hall U Penn.JPG
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