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Chlorite Group

 
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The chlorites are a group of phyllosilicate
Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
 mineral
Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s. Chlorites can be described by the following four endmembers
Solid solution

A solid solution is a solid-phase solution of one or more soluble in a solvent. Such a mixture is considered a solution rather than a Chemical compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single wiktionary:Homogeneous phase ....
 based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn.

In addition, zinc, lithium, and calcium species are known. The great range in composition results in considerable variation in physical, optical, and X-ray properties. Similarly, the range of chemical composition allows chlorite group minerals to exist over a wide range of temperature and pressure conditions.






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The chlorites are a group of phyllosilicate
Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
 mineral
Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s. Chlorites can be described by the following four endmembers
Solid solution

A solid solution is a solid-phase solution of one or more soluble in a solvent. Such a mixture is considered a solution rather than a Chemical compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single wiktionary:Homogeneous phase ....
 based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn.
  • Clinochlore: (Mg5Al)(AlSi3)O10(OH)8
  • Chamosite: (Fe5Al)(AlSi3)O10(OH)8
  • Nimite: (Ni5Al)(AlSi3)O10(OH)8
  • Pennantite: (Mn,Al)6(Si,Al)4O10(OH)8


In addition, zinc, lithium, and calcium species are known. The great range in composition results in considerable variation in physical, optical, and X-ray properties. Similarly, the range of chemical composition allows chlorite group minerals to exist over a wide range of temperature and pressure conditions. For this reason chlorite minerals are ubiquitous minerals within low and medium temperature metamorphic rocks, some igneous rocks, hydrothermal
Hydrothermal circulation

Hydrothermal circulation in its most general sense is the circulation of hot water; 'hydros' in the Greek meaning water and 'thermos' meaning heat....
 rocks and deeply buried sediments.

Chlorite structure

The typical general formula is: (Mg,Fe)3(Si,Al)4O10(OH)2·(Mg,Fe)3(OH)6. This formula emphasises the structure of the group.

Chlorites have a 2:1 sandwich structure (2:1 sandwich layer = tetrahedral-octahedral-tetrahedral = t-o-t...), this is often referred to as a talc
Talc

Talc is a mineral composed of hydrated magnesium silicate with the chemical formula Hydrogen2Magnesium34 or Magnesium3Silicon4Oxygen102....
 layer. Unlike other 2:1 clay minerals, a chlorite's interlayer space (the space between each 2:1 sandwich filled by a cation) is comprised of (Mg2+, Fe3+)(OH)6. This (Mg2+, Fe3+)(OH)6 unit is more commonly referred to as the brucite
Brucite

Brucite is the mineral form of magnesium hydroxide, with the chemical formula Magnesium2. It is pearly white or pale green in colour, translucent, with perfect cleavage, and tabular crystals or massive....
-like layer, due to its closer resemblance to the mineral brucite (Mg(OH)2). Therefore, chlorite's structure appears as follows:
-t-o-t-brucite-t-o-t-brucite ...


An older classification divided the chlorites into two subgroups: the orthochlorites and leptochlorites. The terms are seldom used and the ortho prefix is somewhat misleading as the chlorite crystal system is monoclinic and not orthorhombic.

Occurrence

Chlorite is commonly found in igneous rock
Igneous rock

Igneous rock is one of the three main Rock types . Igneous rock is formed by magma being cooled and becoming solid . They may form with or without crystallization, either below the surface as Intrusion rocks or on the surface as extrusive rocks....
s as an alteration product of mafic
Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
 minerals such as pyroxene
Pyroxene

The pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rock rock . They share a common structure comprised of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems....
, amphibole
Amphibole

Amphibole defines an important group of generally dark-colored rock-forming Silicate minerals minerals, composed of double chain SiO4 tetrahedron, linked at the vertices and generally containing ions of iron and/or magnesium in their structures....
, and biotite
Biotite

Biotite is a common Silicate minerals#Phyllosilicates mineral within the mica group, with the approximate chemical formula K3AlSi3O102....
. Chlorite is a common mineral associated with hydrothermal ore
Ore

An ore is a type of Rock that contains minerals such as gemstones and metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals suc...
 deposits and commonly occurs with epidote
Epidote

Epidote is a calcium aluminium iron Silicate minerals mineral, Ca2Al2O, crystallizing in the monoclinic system. Well-developed crystals are of frequent occurrence: they are commonly prismatic in habit, the direction of elongation being perpendicular to the single plane of symmetry....
, sericite
Sericite

Sericite is a fine grained mica, either muscovite, illite, or paragonite. Sericite is a common alteration mineral of orthoclase or plagioclase feldspars in areas that have been subjected to hydrothermal alteration typically associated with copper, tin, or other hydrothermal ore deposits....
, adularia
Adularia

Adularia is a Silicate minerals mineral with formula potassiumaluminumsilicon3oxygen8. It is a form of orthoclase which crystallizes at unusually low temperatures....
 and sulfide mineral
Sulfide mineral

A sulfide mineral is a mineral containing sulfide as the major anion. Sulfides are economically important as metal ores. The sulfide class also includes the selenide mineral, the telluride mineral, the arsenide mineral, the antimonide mineral, the bismuthinides, and the sulfosalts ....
s. In this environment chlorite may be a retrograde metamorphic alteration mineral of existing ferromagnesian minerals, or it may be present as a metasomatism
Metasomatism

Metasomatism is the chemical alteration of a Rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or Metamorphism source....
 product via addition of Fe, Mg, or other compounds into the rock mass. Chlorite is also a common metamorphic
Metamorphic rock

Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form"....
 mineral, usually indicative of low-grade metamorphism. It is the diagnostic species of the zeolite
Zeolite

Zeolites are Microporous material, aluminosilicate minerals commonly used as commercial absorbents. The term zeolite was originally coined in 1756 by Sweden mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that had been absorbed by the material....
 facies and of lower greenschist
Greenschist

Greenschist - also known as greenstone - is a general field petrology term applied to metamorphic rocks and/or altered mafic volcanic rock....
 facies. It occurs in the quartz
Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
, albite
Albite

Albite is a plagioclase feldspar mineral. It is the sodium Endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content....
, sericite
Sericite

Sericite is a fine grained mica, either muscovite, illite, or paragonite. Sericite is a common alteration mineral of orthoclase or plagioclase feldspars in areas that have been subjected to hydrothermal alteration typically associated with copper, tin, or other hydrothermal ore deposits....
, chlorite, garnet
Garnet

The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" comes from the Latin language granatus , possibly a reference to the Punica granatum , a plant with red seeds similar in shape, size, and color to some garnet crystals....
 assemblage of pelitic schist
Schist

The schists form a group of Erins metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, Chlorite group, talc, hornblende, graphite, and others....
. Within ultramafic rocks, metamorphism can also produce predominantly clinochlore chlorite in association with talc
Talc

Talc is a mineral composed of hydrated magnesium silicate with the chemical formula Hydrogen2Magnesium34 or Magnesium3Silicon4Oxygen102....
. Experiments indicate that chlorite can be stable in peridotite of the Earth's mantle above the ocean lithosphere
Lithosphere

File:Plates tect2 en.svgFile:Earth-crust-cutaway-english.svgThe lithosphere is the rigid outermost shell of a rocky planet....
 carried down by subduction
Subduction

In geology, subduction is the process that takes place at convergent boundary by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge....
, and chlorite may even be present in the mantle volume from which island arc magma
Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
s are generated.

Chlorite occurs naturally in a variety of locations and forms. For example, chlorite is found naturally in certain parts of Wales
Wales

native_name = Cymru|conventional_long_name = Wales|common_name = Wales|image_flag = Flag of Wales 2.svg|national_motto = ...
 in mineral schists. Chlorite is found in large boulders scattered on the ground surface on Ring Mountain
Ring Mountain (California)

Ring Mountain is an elevated landform on the Tiburon Peninsula in Marin County, California, California, United States. This mountain was named for George E....
 in Marin County, California
California

California is a U.S. state on the West Coast of the United States of the United States, along the Pacific Ocean. It is bordered by Oregon to the north, Nevada to the east, Arizona to the southeast, and to the south the Mexico state of Baja California....
.

Members of the Chlorite group:


Baileychlore (Zn,Fe+2,Al,Mg)6(Al,Si)4O10(O,OH)8
Chamosite (Fe,Mg)5Al(Si3Al)O10(OH)8
Clinochlore (Mg,Fe2+)5Al(Si3Al)O10(OH)8
Cookeite LiAl4(Si3Al)O10(OH)8
Donbassite Al2[Al2.33][Si3AlO10](OH)8
Gonyerite (Mn,Mg)5(Fe+3)2Si3O10(OH)8
Nimite (Ni,Mg,Al)6(Si,Al)4O10(OH)8
Odinite (Fe,Mg,Al,Fe,Ti,Mn)2.4(Al,Si)2O5OH4
Orthochamosite (Fe+2,Mg,Fe+3)5Al(Si3Al)O10(O,OH)8
Pennantite (Mn5Al)(Si3Al)O10(OH)8
Ripidolite (Mg,Fe,Al)6(Al,Si)4O10(OH)8
Sudoite Mg2(Al,Fe)3Si3AlO10(OH)8


Clinoclore, pennantite, and chamosite are the most common varieties. Several other sub-varieties have been described.

The name chlorite is from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 chloros, meaning "green", in reference to its color.

See also

  • List of minerals
    List of minerals

    This is a List of minerals for which there are Wikipedia articles. Mineral variety names and mineraloids are to be listed after the valid minerals for each letter....