Actinolite

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Actinolite is an inorganic compound belonging to the amphibole group of minerals. It is a member of the inosilicate subclass and is composed of double chain silicates. Actinolite is commonly found in metamorphic rocks and is known for its characteristic green color.

Composition and Structure

Actinolite has the chemical formula: Ca2(Mg,Fe)5Si8O22(OH)2. It is composed of calcium, magnesium, iron, silicon, oxygen, and hydrogen. The presence of iron and magnesium in varying amounts gives actinolite its range of colors from green to black. The mineral crystallizes in the monoclinic crystal system and forms elongated, prismatic crystals.

Formation and Occurrence

Actinolite is typically formed through the metamorphism of mafic rocks, such as basalt and gabbro, under conditions of medium to high temperature and pressure. It is commonly found in schist and gneiss, which are types of metamorphic rocks. Actinolite can also occur in contact metamorphism zones where igneous intrusions have altered surrounding rocks.

Physical Properties

Actinolite has a Mohs hardness of 5 to 6, making it relatively hard. It has a specific gravity of 3.0 to 3.2 and exhibits two directions of perfect cleavage. The mineral has a vitreous to silky luster and is translucent to opaque. Its color ranges from light to dark green, depending on the iron content.

Uses

Actinolite is primarily of interest to geologists and mineralogists for its role in understanding metamorphic processes. It is also used as a gemstone, although it is not as popular as other minerals due to its relative softness and cleavage. In the past, actinolite was used as an asbestos material, but this use has been discontinued due to health concerns.

Health Concerns

Actinolite, like other forms of asbestos, can pose serious health risks if its fibers are inhaled. Prolonged exposure to actinolite fibers can lead to respiratory diseases such as asbestosis, lung cancer, and mesothelioma. Due to these health risks, the use of actinolite in commercial products has been heavily regulated.

See Also

• Amphibole
• Metamorphic rock
• Asbestos
• Silicate minerals