Amphiboles
Introduction
Amphiboles are a group of minerals that are hydrous silicates. They are characterized by their dark color, hardness, and two cleavage directions that intersect at approximately 60 and 120 degrees. Amphiboles are complex in nature, with a general formula of (A)0-1B2C5T8O22(OH)2. In this formula, A represents alkali metals, B represents alkaline earth metals, C represents metals like aluminum, iron, and magnesium, and T represents silicon or aluminum.
Classification
Amphiboles are classified into two main groups: ortho-amphiboles and clino-amphiboles. Ortho-amphiboles are characterized by their orthorhombic crystal system, while clino-amphiboles are characterized by their monoclinic crystal system. The most common ortho-amphibole is anthophyllite, while the most common clino-amphibole is hornblende.
Structure
The structure of amphiboles is composed of double chains of tetrahedra, which are linked by octahedra and additional tetrahedra. The double chains are parallel to the c-axis and are cross-linked by B and C cations. The A sites are usually vacant, but can be filled with alkali metals in some amphiboles.
Formation
Amphiboles are typically formed in metamorphic and igneous rocks. In metamorphic rocks, they are formed through the metamorphism of magnesium-rich rocks. In igneous rocks, they are formed through the crystallization of magma or lava.
Properties
Amphiboles have several distinctive properties. They are generally dark in color, with a hardness of 5-6 on the Mohs scale of hardness. They also have two cleavage directions that intersect at approximately 60 and 120 degrees. Additionally, amphiboles are pleochroic, meaning they exhibit different colors when viewed from different angles.
Uses
Amphiboles have a variety of uses. They are used as a source of asbestos, which is used in insulation and fireproof materials. They are also used in the manufacture of ceramics and glass. Additionally, amphiboles are used in the study of geologic processes, as they can provide information about the conditions under which they were formed.
Health Risks
Certain types of amphiboles, such as those that contain asbestos, can pose health risks. Asbestos fibers can be inhaled and can cause diseases such as asbestosis, lung cancer, and mesothelioma.