Serpentine subgroup
Introduction
The serpentine subgroup is a classification of minerals that are part of the larger kaolinite-serpentine group. These minerals, which include antigorite, chrysotile and lizardite, are characterized by their layered structure and are typically green in color due to the presence of iron. The serpentine subgroup is named after the serpent-like appearance of these minerals, which often exhibit a scaly or fibrous texture.
Formation and Occurrence
Serpentine minerals are formed through the process of serpentinization, a geological phenomenon that involves the alteration of ultramafic rocks by water. This process occurs under specific conditions of temperature and pressure, typically in the Earth's mantle or at tectonic plate boundaries. The resulting serpentine minerals are often found in association with other minerals such as magnetite, brucite, and talc.
Mineralogy
The serpentine subgroup is characterized by a layered structure, with each layer composed of a sheet of tetrahedrons linked by octahedrons. The tetrahedrons are typically composed of silicon and oxygen, while the octahedrons are composed of magnesium and hydroxyl groups. This structure results in a low hardness and a greasy or waxy luster, which are characteristic features of serpentine minerals.
Antigorite
Antigorite is a high-temperature serpentine mineral that is characterized by its platy morphology and green color. It is often found in metamorphic rocks and is a common constituent of serpentinite, a rock formed by the serpentinization of ultramafic rocks.
Chrysotile
Chrysotile, also known as white asbestos, is a fibrous serpentine mineral that is often used in the construction industry due to its heat-resistant properties. However, its use has been largely discontinued due to health concerns associated with asbestos exposure.
Lizardite
Lizardite is the most common serpentine mineral and is characterized by its scaly morphology and light green color. It is often found in association with chrysotile and antigorite in serpentinite rocks.
Uses and Applications
Serpentine minerals have a wide range of uses and applications. Due to their heat-resistant properties, they were historically used in the production of asbestos, a material used for fireproofing and insulation. However, this use has been largely discontinued due to health concerns associated with asbestos exposure. Today, serpentine minerals are often used in the production of decorative items such as jewelry and carvings, due to their attractive green color and ease of carving.
Environmental and Health Concerns
Exposure to serpentine minerals, particularly chrysotile, can pose significant health risks. When inhaled, the fibrous structure of these minerals can cause lung diseases such as asbestosis and mesothelioma. As such, the mining and handling of serpentine minerals are subject to strict regulations to protect workers and the environment.