Chlorite group

The chlorite group comprises typically green sheet-silicate minerals with layered structures. Its members commonly form when other minerals are altered by heat, fluids, or weathering.

Phyllosilicate: A silicate mineral built from sheets of linked tetrahedra and octahedra. Chlorites belong to this broad structural class of sheet silicates.
Chloritization: The formation of chlorite through alteration of pre-existing minerals or rocks. This alteration process produces chlorite group minerals in many geological settings.
Greenschist: A metamorphic rock dominated by green minerals such as chlorite, actinolite, and epidote. Chlorite is a characteristic mineral in many greenschists.
Mica: A group of sheet silicate minerals characterized by strong basal cleavage and potassium-bearing interlayers. Micas have potassium-rich interlayers, unlike chlorite's brucite-like hydroxide layers.
Tetrahedral sheet: A sheet of silicate tetrahedra linked through shared oxygen atoms. Silica tetrahedral sheets form part of each chlorite layer.
Hydrothermal alteration: Chemical and mineralogical change caused by hot, circulating fluids within rocks. Hydrothermal fluids can supply or redistribute elements needed to form chlorite.
Greenschist facies: A range of metamorphic conditions commonly marked by chlorite, actinolite, and epidote in suitable rocks. Chlorite abundance and composition help identify this low- to intermediate-grade facies.
Kaolinite: A 1:1 clay mineral composed of one silica tetrahedral sheet bonded to one alumina octahedral sheet. Kaolinite has a simpler 1:1 layer structure rather than chlorite's alternating layers.
Octahedral sheet: A sheet of cations coordinated by oxygen or hydroxyl groups in octahedral arrangements. Octahedral sheets provide chlorite's metal-rich structural layers.
Metamorphism: Solid-state mineralogical and textural change in rocks under altered pressure, temperature, or chemical conditions. Chlorite commonly develops during low-grade metamorphic reactions.

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