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The chlorites are a group of
phyllosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide) is usually conside ...
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 Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with t ...
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 Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí ...
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 layer. Unlike other 2:1 clay minerals, a chlorite's interlayer space (the space between each 2:1 sandwich filled by a cation) is composed of . This unit is more commonly referred to as the 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 rocks as an alteration product of mafic minerals such as pyroxene, amphibole, and biotite. In this environment chlorite may be a retrograde metamorphic alteration mineral of existing ferromagnesian minerals, or it may be present as a metasomatism product via addition of Fe, Mg, or other compounds into the rock mass. Chlorite is a common mineral associated with hydrothermal ore deposits and commonly occurs with epidote, sericite, adularia and sulfide minerals. Chlorite is also a common metamorphic rock, metamorphic mineral, usually indicative of low-grade metamorphism. It is the diagnostic species of the zeolite facies and of lower greenschist facies. It occurs in the quartz, albite, sericite, chlorite, garnet assemblage of pelitic schist. Within ultramafic rocks, metamorphism can also produce predominantly clinochlore chlorite in association with talc. Experiments indicate that chlorite can be stable in peridotite of the Earth's mantle above the ocean lithosphere carried down by subduction, and chlorite may even be present in the mantle volume from which island arc magmas are generated. Chlorite occurs naturally in a variety of locations and forms. For example, chlorite is found naturally in certain parts of Wales in mineral schists. Chlorite is found in large boulders scattered on the ground surface on Ring Mountain (California), Ring Mountain in Marin County, 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 deposit in the Irkutsk Oblast of Eastern Siberia.


Distinguishing from other minerals

Chlorite forms blue-green crystals resembling mica. However, while the plates are flexible, they are not elastic like mica, and are less easily pulled apart. 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 *Thuringite


References

* * * * *]


External links

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