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The chlorites are a group of
phyllosilicate Silicate minerals are rock-forming mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology) ...
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

mineral
s. Chlorites can be described by the following four
endmember An endmember (also end-member or end member) in mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical mineralogy, optical) properties of minerals and ...
s 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 An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Moti ...
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 in its most general sense is the circulation of hot water (Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC ...
rocks and deeply buried sediments. The name ''chlorite'' is from the
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
''chloros'' (χλωρός), meaning "green", in reference to its color. They do not contain the element
chlorine Chlorine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemica ...

chlorine
, also named from the same Greek root.


Chlorite structure

The typical general formula is: . This formula emphasizes 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, or talcum, is a clay mineral Clay minerals are , sometimes with variable amounts of , , s, s, and other s found on or near some s. Clay minerals form in the presence of water and have been important to life, and many theories of ...

talc
layer. Unlike other 2:1 clay minerals, a chlorite's interlayer space (the space between each 2:1 sandwich filled by a
cation An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are u ...
) is composed of . This unit is more commonly referred to as the
brucite Brucite is the mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it i ...

brucite
-like layer, due to its closer resemblance to the mineral brucite (). Therefore, chlorite's structure appears as follows: : -t-o-t-brucite-t-o-t-brucite ... That's why they are also called 2:1:1 minerals. 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 (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock i ...
s as an alteration product of
mafic A mafic mineral or rock is a silicate mineral Silicate minerals are rock-forming mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composit ...
minerals such as
pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming Silicate minerals#Inosilicates, inosilicate minerals found in many Igneous rock, igneous and metamorphic rock, metamorphic rock (geology), rocks. Pyroxenes have t ...
,
amphibole Amphibole () is a group of Silicate minerals, inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedron, tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their s ...

amphibole
, and
biotite Biotite is a common group of phyllosilicate Silicate minerals are rock-forming mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science conce ...

biotite
. In this environment chlorite may be a retrograde metamorphic alteration mineral of existing ferromagnesian minerals, or it may be present as a
metasomatism Metasomatism (from the Greek μετά (change) and σῶμα (body)) is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical composition. The miner ...
product via addition of Fe, Mg, or other compounds into the rock mass. Chlorite is a common mineral associated with
hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC ...
ore ore – psilomelane Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

ore
deposits and commonly occurs with
epidote Epidote is a calcium aluminium iron Silicate minerals, sorosilicate mineral. Description Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly ...

epidote
,
sericite A sample of sericite Sericite is the name given to very fine, ragged grains and Aggregate (geology), aggregates of white (colourless) micas, typically made of muscovite, illite, or paragonite. Sericite is produced by the alteration of orthoclase or ...
,
adularia
adularia
and
sulfide mineral The sulfide minerals are a class of s containing (S2−) or (S22−) as the major . Some sulfide minerals are economically important as metal s. The sulfide class also includes the , the , the , the , the bismuthinides, the s and the s.http://w ...
s. Chlorite is also a common
metamorphic Metamorphic rocks arise from the transformation of existing rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the mineral ...

metamorphic
mineral, usually indicative of low-grade metamorphism. It is the diagnostic species of the
zeolite Zeolites are microporous, aluminosilicate Aluminosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Eart ...

zeolite
facies and of lower
greenschist Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite, ...
facies. It occurs in the
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...

quartz
,
albite Albite is a . It is the sodium of the plagioclase series. It represents a plagioclase with less than 10% content. The pure albite endmember has the formula 38. It is a . Its color is usually pure white, hence its name from ''albus''. It is ...

albite
,
sericite A sample of sericite Sericite is the name given to very fine, ragged grains and Aggregate (geology), aggregates of white (colourless) micas, typically made of muscovite, illite, or paragonite. Sericite is produced by the alteration of orthoclase or ...
, chlorite,
garnet Garnets () are a group of silicate mineral Silicate minerals are rock-forming mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science c ...

garnet
assemblage of
pelitic Image:Petrogenetic grid for Metapelites.png, upright=1.4, Petrogenetic grid for metapelites (click to zoom). Each line represents a metamorphic reaction. Metamorphic facies included are: BS = Blueschist facies, EC = Eclogite facies, PP = Prehnite-P ...
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fair ...

schist
. Within ultramafic rocks, metamorphism can also produce predominantly clinochlore chlorite in association with
talc Talc, or talcum, is a clay mineral Clay minerals are , sometimes with variable amounts of , , s, s, and other s found on or near some s. Clay minerals form in the presence of water and have been important to life, and many theories of ...

talc
. Experiments indicate that chlorite can be stable in peridotite of the
Earth's mantle Earth's mantle is a layer of silicate mineral, silicate rock between the Earth's crust, crust and the Earth's outer core, outer core. It has a mass of 4.01 × 1024 kg and thus makes up 67% of the mass of Earth. It has a thickness of making up a ...
above the ocean
lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion o ...
carried down by
subduction Subduction is a geological process in which the oceanic lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. O ...

subduction
, and chlorite may even be present in the mantle volume from which
island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries (such as the Ring of Fire). Most island arcs originate on oceanic crust and have resulted from the descent of the litho ...

island arc
magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others ...

magma
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 ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, and the Bristol Channel to the south. It ...

Wales
in mineral schists. Chlorite is found in large boulders scattered on the ground surface on Ring Mountain in
Marin County Marin County is located in the northwestern part of the San Francisco Bay Area of the U.S. state of California. As of the 2010 United States Census, 2010 census, the population was 252,409. Its county seat is San Rafael, California, San Rafael. ...
,
California California is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper i ...

California
.


Members of the chlorite group

: Clinochlore, pennantite, and chamosite are the most common varieties. Several other sub-varieties have been described. A massive compact variety of clinochlore used as a decorative carving stone is referred to by the trade name seraphinite. It occurs in the Korshunovskoye iron
skarn Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism Metasomatism (from the Greek μετά (change) and σῶμα (body)) is the chemical alteration of a rock by hydrothermal and other fluids. ...

skarn
deposit in the
Irkutsk Oblast Irkutsk Oblast (russian: Ирку́тская о́бласть, Irkutskaya oblast; bua, Эрхүү можо, Erkhüü mojo) is a federal subjects of Russia, federal subject of Russia (an oblast), located in southeastern Siberia in the basins of ...
of Eastern
Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of R ...

Siberia
.


Distinguishing from other minerals

Chlorite forms blue-green crystals resembling
mica Micas ( ) are a group of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs natural ...

mica
. However, while the plates are flexible, they are not elastic like mica, and are less easily pulled apart.
Talc Talc, or talcum, is a clay mineral Clay minerals are , sometimes with variable amounts of , , s, s, and other s found on or near some s. Clay minerals form in the presence of water and have been important to life, and many theories of ...

Talc
is much softer and feels soapy between fingers.


Uses

Various types of chlorite stone have been used as raw material for carving into sculptures and vessels since prehistoric times.


See also

*
List of minerals This is a list of minerals for which there are articles on Wikipedia. Mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific ...
* Thuringite


References

* * * * *]


External links

{{DEFAULTSORT:Chlorite Group Clay minerals group Monoclinic minerals Phyllosilicates