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Serpentine subgroup

earth science Maturity 7-9 Next article →

The serpentine subgroup is a collection of common rock-forming minerals. These minerals are hydrous magnesium iron phyllosilicates. This scientific name means they contain water and are made of magnesium, iron, and silicate layers. They are often greenish, brownish, or spotted in appearance. The name comes from the Latin word "serpentinus," which means "snake-like." This describes their smooth or scaly look.

These minerals are important to both geology and industry. They serve as sources of magnesium and asbestos. They are also used as beautiful decorative stones.

Serpentine minerals form through a process called serpentinization. This occurs when water interacts with ultramafic rocks, such as those rich in olivine. This chemical reaction changes the original minerals into serpentine minerals. This process can happen at temperatures between 0 and approximately 600 degrees Celsius. Serpentinization occurs in many geological systems. It happens in terrestrial environments like subduction zones and transform faulting. It also occurs in oceanic hydrothermalism and even in extraterrestrial environments.

Serpetine chemical structure
Serpetine chemical structure

This process can also happen through the metamorphic alteration of peridotite and pyroxene.

All serpentine minerals share the same chemical formula. However, they are polymorphs. This means their atoms are arranged into different crystal lattices or structures. There are three important mineral polymorphs in this subgroup. The first is antigorite, which has a platy habit. A platy habit means the mineral looks like flat plates. The second is lizardite, which also has a platy habit. The third is chrysotile, which has a fibrous habit. This means it forms long, thin, thread-like particles.

Antigorite (Var. Bowenite)
Antigorite (Var. Bowenite)

Because of these different structures, the minerals can look very different.

Antigorite is a very important polymorph in the Earth's crust. It is the type that most commonly forms during the metamorphism of wet ultramafic rocks. It is also the most stable at high temperatures. It can remain stable at temperatures over 600 degrees Celsius at depths of 30 to 50 kilometers. Antigorite contains about 13 percent water by weight. Because it holds so much water, it may help transport water into the Earth. This happens in subduction zones. The water is later released to help create magmas in island arcs.

Humans have used serpentine for many different purposes throughout history. Some varieties are called "noble" or "precious" serpentine. These are used as gems and for ornamental carvings. In the historic Punjab province of India, craftsmen used a pure green serpentine. They called it "false jade" in English. They used it to make cups, ornamental sword hilts, and dagger handles.

Serpentine paten Louvre MR415
Serpentine paten Louvre MR415

In New Zealand, the Māori people carved objects from local serpentine. They called the mineral "tangiwai," which means "tears."

Budai in serpentine, height 8 cm arp
Budai in serpentine, height 8 cm arp

In the Roman era, a type of serpentinite called verde antique was used as decorative stone.

Serpentine is also used in modern industry. It can be used for railway ballasts and building materials. The asbestiform type, specifically chrysotile, is used for thermal and electrical insulation. However, there are safety concerns. When serpentine is excavated, asbestos can be released into the air. If used as a road surface, breathing it in is a long-term health hazard. The EPA states that there is an increased risk of developing benign intestinal polyps from ingestion. Some forms of serpentine also react with carbon dioxide to release oxygen back into the atmosphere.

Finally, serpentine can change the environment around it. Soils derived from these rocks can be toxic to many plants. This is because the soil has high levels of nickel, chromium, and cobalt. It also has low levels of potassium and phosphorus. These conditions create unique ecosystems called serpentine barrens. In these areas, you will see strips of shrubland and scattered small trees. These areas look different from the surrounding forests because only specialized, slow-growing species can survive there.

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🖼️ Images & Media (5)
File:Serpentyn, 2Polska.jpg
Serpentyn, 2Polska.jpg
File:Serpetine chemical structure.png
Serpetine chemical structure.png
File:Serpentine paten Louvre MR415.jpg
Serpentine paten Louvre MR415.jpg
File:Budai in serpentine, height 8 cm arp.jpg
Budai in serpentine, height 8 cm arp.jpg
File:Antigorite (Var. Bowenite).jpg
Antigorite (Var. Bowenite).jpg
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