Chlorite group
Overview
The Chlorite group refers to a family of phyllosilicate minerals that are commonly found in igneous, metamorphic, and sedimentary rocks. They are characterized by their green color and are part of the larger group of sheet silicate minerals known as clay minerals.
Composition and Structure
Chlorites are hydrous aluminum-iron-magnesium silicates, with a general chemical formula of (Mg,Fe2+)3(Al,Si)4O10(OH)2(Mg,Fe2+)3(OH)6. They are composed of alternating layers of tetrahedral and octahedral sheets. The tetrahedral sheets are composed of silicon-oxygen tetrahedra, while the octahedral sheets are composed of hydroxide octahedra.
Physical Properties
Chlorite minerals are typically green in color, although they can also be black or brown. They have a hardness of 2-2.5 on the Mohs scale, and a specific gravity of 2.6-3.3. Chlorites exhibit perfect cleavage in one direction and have a pearly to vitreous luster.
Occurrence and Formation
Chlorite minerals are commonly found in the alteration products of ferromagnesian minerals such as pyroxenes, amphiboles, and biotite. They also occur as alteration products in olivine and feldspars in igneous rocks, and in low-grade metamorphic rocks such as greenschists and phyllites.
Uses and Significance
Chlorite minerals are not typically used as a source of metal ores. However, they are important indicators of metamorphic conditions and can be used to understand the history and evolution of the Earth's crust. In addition, chlorites are used in the petroleum industry as indicators of the depth of oil and gas deposits.