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| {{Other uses}}
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| {{Infobox mineral
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| | name = Garnet
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| | category = [[Nesosilicate]]
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| | boxwidth =
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| | boxbgcolor =
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| | boxwidth =
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| | boxbgcolor = #FF9977
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| | boxtextcolor = black
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| | image = GarnetCrystalUSGOV.jpg
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| | caption =
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| | formula = The general formula <!--
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| -->''X''<sub>3</sub>''Y''<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| | molweight =
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| | Z = 8
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| | spacegroup = Ia3d
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| | crystalclass = <math>4/m\bar{3} 2/m</math>
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| | color = virtually all colors
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| | habit = [[Rhombic dodecahedron]] or cubic
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| | system = [[Cubic (crystal system)|Cubic]] rhombic dodecahedron, icositetrahedron
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| | twinning =
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| | cleavage = Indistinct
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| | fracture = conchoidal to uneven
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| | mohs = 6.5–7.5
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| | luster = vitreous to resinous
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| | polish = vitreous to subadamantine<ref name="GRG"/>
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| | refractive = 1.72–1.94
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| | opticalprop = Single refractive, often anomalous double refractive<ref name="GRG"/>
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| | birefringence = None
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| | pleochroism = None
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| | streak = White
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| | gravity = 3.1–4.3
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| | melt =
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| | fusibility =
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| | diagnostic =
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| | solubility =
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| | diaphaneity =
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| | other =
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| | var1 = Pyrope | var1text = Mg<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub>
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| | var2 = Almandine | var2text = Fe<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub>
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| | var3 = Spessartine | var3text = Mn<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub>
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| | var4 = Andradite | var4text = Ca<sub>3</sub>Fe<sub>2</sub>Si<sub>3</sub>O<sub>12</sub>
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| | var5 = Grossular | var5text = Ca<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub>
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| | var6 = Uvarovite | var6text = Ca<sub>3</sub>Cr<sub>2</sub>Si<sub>3</sub>O<sub>12</sub>
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| }}
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| '''Garnets''' {{IPAc-en|ˈ|ɡ|ɑr|n|ə|t}} are a group of [[silicate mineral]]s that have been used since the [[Bronze Age]] as [[gemstone]]s and [[abrasives]].{{#tag:ref|The word ''garnet'' comes from 14th‑century [[Middle English]] word ''gernet'' meaning 'dark red,' from the [[Latin language|Latin]] ''granatus,'' from ''granum'' ('[[grain]], [[seed]]') + suffix ''atus,'' possibly a reference to ''mela granatum'' or even ''pomum granatum'' ('[[pomegranate]]',<ref>[http://www.etymonline.com/index.php?term=pomegranate pomegranate]. Online Etymology Dictionary. Retrieved on 2011-12-25.</ref> scientific name: ''Punica granatum''), a plant whose fruits contain abundant and vivid red [[aril]]s, are similar in shape, size, and color to some garnet crystals.<ref>[http://www.etymonline.com/index.php?term=garnet garnet]. Online Etymology Dictionary. Retrieved on 2011-12-25.</ref>|group="note"}}
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| All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different species are [[pyrope]], [[almandine]], [[spessartine]], [[grossular]] (varieties of which are [[hessonite]] or cinnamon-stone and [[tsavorite]]), [[uvarovite]] and [[andradite]]. The garnets make up two [[solid solution]] series: pyrope-almandine-spessarite and uvarovite-grossular-andradite.
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| ==Physical properties==
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| ===Properties===
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| Garnet species are found in many colors including red, orange, yellow, green, purple, brown, blue, black, pink and colorless. The rarest of these is the blue garnet, discovered in the late 1990s in Bekily, [[Madagascar]]. It is also found in parts of the [[United States]], [[Russia]], [[Kenya]], [[Tanzania]], and [[Turkey]]. It changes color from blue-green in the daylight to purple in [[incandescent]] light, as a result of the relatively high amounts of [[vanadium]] (about 1 wt.% V<sub>2</sub>O<sub>3</sub>). Other varieties of color-changing garnets exist. In daylight, their color ranges from shades of green, beige, brown, gray, and blue, but in incandescent light, they appear a reddish or purplish/pink color. Because of their color-changing quality, this kind of garnet is often mistaken for [[Chrysoberyl|Alexandrite]].
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| [[File:Garnet.JPG|thumb|Right|A sample showing the deep red color garnet can exhibit.]]
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| Garnet species' light transmission properties can range from the gemstone-quality transparent specimens to the opaque varieties used for industrial purposes as abrasives. The mineral's [[lustre (mineralogy)|luster]] is categorized as [[vitreous lustre|vitreous]] (glass-like) or resinous (amber-like).
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| ===Crystal structure===
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| [[File:Garnet s.jpg|thumb|right|Crystal structure model of garnet]]
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| Garnets are [[Silicate minerals#Nesosilicates or Isosilicates|nesosilicates]] having the general formula ''X''<sub>3</sub>''Y''<sub>2</sub>([[silicon|Si]] [[oxygen|O]]<sub>4</sub>)<sub>3</sub>. The ''X'' site is usually occupied by divalent cations ([[calcium|Ca]]<sup>2+</sup>, [[magnesium|Mg]]<sup>2+</sup>, [[iron|Fe]]<sup>2+</sup>) and the ''Y'' site by trivalent cations ([[aluminium|Al]]<sup>3+</sup>, Fe<sup>3+</sup>, [[chromium|Cr]]<sup>3+</sup>) in an [[octahedron|octahedral]]/[[tetrahedron|tetrahedral]] framework with [SiO<sub>4</sub>]<sup>4−</sup> occupying the tetrahedra.<ref>{{cite web | last = Smyth | first = Joe | title = Mineral Structure Data | work = Garnet| publisher = University of Colorado| url = http://ruby.colorado.edu/~smyth/min/garnet.html | accessdate = 2007-01-12 }}</ref> Garnets are most often found in the [[dodecahedral]] [[crystal habit]], but are also commonly found in the trapezohedron habit. (Note: the word "trapezohedron" as used here and in most mineral texts refers to the shape called a [[Deltoidal icositetrahedron]] in solid geometry.) They crystallize in the [[Cubic (crystal system)|cubic]] system, having three axes that are all of equal length and perpendicular to each other. Garnets do not show [[Cleavage (crystal)|cleavage]], so when they fracture under stress, sharp irregular pieces are formed.
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| ===Hardness===
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| Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this mineral group shows a range of hardness on the [[Mohs scale of mineral hardness|Mohs scale]] of about 6.5 to 7.5. The harder species like [[almandine]] are often used for abrasive purposes.
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| ===Magnetics used in garnet series identification===
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| For gem identification purposes, a pick-up response to a strong neodymium magnet separates garnet from all other natural transparent gemstones commonly used in the jewelry trade. [[Magnetic susceptibility]] measurements in conjunction with refractive index can be used to distinguish garnet species and varieties, and determine the composition of garnets in terms of percentages of end-member species within an individual gem.<ref>D. B. Hoover, B. Williams, C. Williams and C. Mitchell, [http://www.stonegrouplabs.com/magnetics_garnetchemistry.pdf Magnetic susceptibility, a better approach to defining garnets], The Journal of Gemmology, 2008, Volume 31, No. 3/4 pp. 91–103</ref> See http://gemstonemagnetism.com.
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| ==Garnet group endmember species==
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| ===Pyralspite garnets – aluminium in ''Y'' site===
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| *[[Almandine]]: Fe<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| *[[Pyrope]]: Mg<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| *[[Spessartine]]: [[manganese|Mn]]<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| ====Almandine====
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| [[File:Almandine.jpeg|thumb|right|Almandine in metamorphic rock]]
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| Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle (though originally almost any red gemstone was known by this name). The term "carbuncle" is derived from the [[Latin]] meaning "live coal" or burning charcoal. The name ''Almandine'' is a corruption of [[Alabanda]], a region in [[Asia Minor]] where these stones were cut in ancient times. Chemically, almandine is an iron-aluminium garnet with the formula Fe<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>; the deep red transparent stones are often called precious garnet and are used as gemstones (being the most common of the gem garnets). Almandine occurs in [[metamorphic rock]]s like [[mica]] [[schist]]s, associated with minerals such as [[staurolite]], [[kyanite]], [[andalusite]], and others. Almandine has nicknames of Oriental garnet, almandine ruby, and carbuncle.
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| ====Pyrope====
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| Pyrope (from the Greek ''pyrōpós'' meaning "fire-eyed") is red in color and chemically a magnesium aluminium [[silicate]] with the formula Mg<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>, though the magnesium can be replaced in part by calcium and ferrous iron. The color of pyrope varies from deep red to black. Pyrope and spessartine gemstones have been recovered from the Sloan diamondiferous [[kimberlite]]s in [[Colorado]], from the Bishop Conglomerate and in a [[Tertiary|Tertiary age]] [[lamprophyre]] at Cedar Mountain in [[Wyoming]].<ref>{{cite book|last=Hausel|first=W. Dan|title=Gemstones and Other Unique Rocks and Minerals of Wyoming – Field Guide for Collectors|year=2000|publisher=Wyoming Geological Survey|location=Laramie, Wyoming|pages=268 p.}}</ref>
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| A variety of pyrope from [[Macon County, North Carolina|Macon County]], [[North Carolina]] is a violet-red shade and has been called ''rhodolite'', Greek for "rose". In chemical composition it may be considered as essentially an isomorphous mixture of pyrope and almandine, in the proportion of two parts pyrope to one part almandine. Pyrope has tradenames some of which are [[misnomer]]s; ''Cape ruby'', ''Arizona ruby'', ''California ruby'', ''Rocky Mountain ruby'', and ''Bohemian garnet'' from the [[Czech Republic]]. Another intriguing find is the blue color-changing garnets from Madagascar, a pyrope-spessartine mix. The color of these [[blue]] garnets is not like sapphire blue in subdued daylight but more reminiscent of the grayish blues and greenish blues sometimes seen in [[spinel]]. However, in white [[LED]] light, the color is equal to the best cornflower blue [[sapphire]], or D block [[tanzanite]]; this is due to the blue garnet's ability to absorb the yellow component of the emitted light.{{citation needed|date=March 2012}}
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| Pyrope is an indicator mineral for high-pressure rocks. The garnets from [[Earth's mantle|mantle]]-derived rocks, [[peridotite]]s, and [[eclogite]]s commonly contain a pyrope variety.
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| ====Spessartine====
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| [[File:Espessartita.jpeg|thumb|right|Spessartine (the reddish mineral)]]
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| Spessartine or spessartite is manganese aluminium garnet, Mn<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>. Its name is derived from [[Spessart]] in [[Bavaria]]. It occurs most often in [[granite]] [[pegmatite]] and allied rock types and in certain low grade metamorphic [[phyllite]]s. Spessartine of an [[orange (color)|orange]]-yellow is found in Madagascar. Violet-red spessartines are found in [[rhyolite]]s in [[Colorado]] and [[Maine]].
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| ===Ugrandite group – calcium in ''X'' site===
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| *[[Andradite]]: Ca<sub>3</sub>Fe<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| *[[Grossular]]: Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| *[[Uvarovite]]: Ca<sub>3</sub>Cr<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| ====Andradite====
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| Andradite is a calcium-iron garnet, Ca<sub>3</sub>Fe<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>, is of variable composition and may be red, yellow, brown, green or black. The recognized varieties are topazolite (yellow or green), [[demantoid]] (green) and [[melanite]] (black). Andradite is found both in deep-seated [[igneous rock]]s like [[syenite]] as well as serpentines, schists, and crystalline limestone. Demantoid has been called the "[[emerald]] of the [[Ural Mountains|Urals]]" from its occurrence there, and is one of the most prized of garnet varieties. Topazolite is a golden-yellow variety and melanite is a black variety.
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| ====Grossular====
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| [[File:GrossularShades.jpg|thumb|right|Grossular on display at the U.S. [[National Museum of Natural History]]. The green gem at right is a type of grossular known as tsavorite.]]
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| Grossular is a calcium-aluminium garnet with the formula Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>, though the calcium may in part be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the [[botany|botanical]] name for the [[gooseberry]], ''grossularia'', in reference to the green garnet of this composition that is found in [[Siberia]]. Other shades include cinnamon brown (cinnamon stone variety), red, and yellow. Because of its inferior hardness to [[zircon]], which the yellow crystals resemble, they have also been called ''hessonite'' from the [[Greek language|Greek]] meaning inferior. Grossular is found in contact metamorphosed [[limestone]]s with [[vesuvianite]], [[diopside]], [[wollastonite]] and [[wernerite]].
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| Grossular garnet from [[Kenya]] and [[Tanzania]] has been called tsavorite. Tsavorite was first described in the 1960s in the [[:Category:Tsavo National Park|Tsavo]] area of Kenya, from which the gem takes its name.<ref>[http://www.mindat.org/min-7836.html Mindat.org - Tsavorite]</ref>
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| ====Uvarovite====
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| Uvarovite is a calcium chromium garnet with the formula Ca<sub>3</sub>Cr<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>. This is a rather rare garnet, bright green in color, usually found as small crystals associated with [[chromite]] in peridotite, [[serpentinite]], and kimberlites. It is found in crystalline [[marble]]s and schists in the [[Ural mountains]] of Russia and [[Outokumpu, Finland]].
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| ===Less common species===
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| *Calcium in ''X'' site
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| **[[Goldmanite]]: Ca<sub>3</sub>V<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| **Kimzeyite: Ca<sub>3</sub>([[zirconium|Zr]],[[titanium|Ti]])<sub>2</sub>[(Si,Al,Fe<sup>3+</sup>)O<sub>4</sub>]<sub>3</sub>
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| **Morimotoite: Ca<sub>3</sub>Ti<sup>4+</sup>Fe<sup>2+</sup>(SiO<sub>4</sub>)<sub>3</sub>
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| **Schorlomite: Ca<sub>3</sub>(Ti<sup>4+</sup>,Fe<sup>3+</sup>)<sub>2</sub>[(Si,Ti)O<sub>4</sub>]<sub>3</sub>
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| *Hydroxide bearing – calcium in ''X'' site
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| **[[Hydrogrossular]]: Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3-x</sub>(OH)<sub>4x</sub>
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| ***Hibschite: Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3-x</sub>(OH)<sub>4x</sub> (where x is between 0.2 and 1.5)
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| ***Katoite: Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3-x</sub>(OH)<sub>4x</sub> (where x is greater than 1.5)
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| *Magnesium or manganese in ''X'' site
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| **[[Knorringite]]: Mg<sub>3</sub>Cr<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| **[[Majorite]]: Mg<sub>3</sub>(Fe<sup>2+</sup>Si)(SiO<sub>4</sub>)<sub>3</sub>
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| **[[Calderite]]: Mn<sub>3</sub>Fe<sup>3+</sup><sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>
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| ====Knorringite====
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| Knorringite is a magnesium-chromium garnet species with the formula Mg<sub>3</sub>Cr<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>. Pure [[endmember]] knorringite never occurs in nature. Pyrope rich in the knorringite component is only formed under high pressure and is often found in [[kimberlite]]s. It is used as an indicator mineral in the search for [[diamond]]s.
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| == Garnet structural group ==
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| *Formula: X<sub>3</sub>Z<sub>2</sub>(TO<sub>4</sub>)<sub>3</sub> (X = Ca, Fe, etc., Z = Al, Cr, etc., T = Si, As, V, Fe, Al)
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| **All are cubic or strongly pseudocubic.
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| {| class="wikitable"
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| |-
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| ! IMA/CNMNC <br>Nickel-Strunz <br>Mineral class !! Mineral name !! Formula !! Crystal system !! Point group !! Space group
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| |-
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| | 04 Oxide || [[Bitikleite-(SnAl)]] || Ca<sub>3</sub>SnSb(AlO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | 04 Oxide || [[Bitikleite-(SnFe)]] || Ca<sub>3</sub>(SnSb<sup>5+</sup>)(Fe<sup>3+</sup>O)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | 04 Oxide || [[Bitikleite-(ZrFe)]] || Ca<sub>3</sub>SbZr(Fe<sup>3+</sup>O<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | 04 Tellurate || [[Yafsoanite]] || Ca<sub>3</sub>Zn<sub>3</sub>(Te<sup>6+</sup>O<sub>6</sub>)<sub>2</sub> || isometric || m{{overline|3}}m <br>or 432 || Ia{{overline|3}}d <br> or I4<sub>1</sub>32
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| |-
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| | 08 Arsenate || [[Berzeliite]] || NaCa<sub>2</sub>Mg<sub>2</sub>(AsO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | 08 Vanadate || [[Palenzonaite]] || NaCa<sub>2</sub>Mn<sup>2+</sup><sub>2</sub>(VO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | 08 Vanadate || [[Schäferite]] || NaCa<sub>2</sub>Mg<sub>2</sub>(VO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |}
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| *IMA/CNMNC – Nickel-Strunz – Mineral subclass: 09.A Nesosilicate
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| **[[Strunz classification|Nickel-Strunz classification]]: 09.AD.25
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| {| class="wikitable"
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| |-
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| ! Mineral name !! Formula !! Crystal system !! Point group !! Space group
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| |-
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| | [[Almandine]] || Fe<sup>2+</sup><sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Andradite]] || Ca<sub>3</sub>Fe<sup>3+</sup><sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Calderite]] || Mn<sup>+2</sup><sub>3</sub>Fe<sup>+3</sup><sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Goldmanite]] || Ca<sub>3</sub>V<sup>3+</sup><sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Grossular]] || Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Henritermierite]] || Ca<sub>3</sub>Mn<sup>3+</sup><sub>2</sub>(SiO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub> || tetragonal || 4/mmm || I4<sub>1</sub>/acd
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| |-
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| | [[Hibschite]] || Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>(3-x)</sub>(OH)<sub>4x</sub> (x= 0.2–1.5) || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Katoite]] || Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>(3-x)</sub>(OH)<sub>4x</sub> (x= 1.5-3) || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Kerimasite]] || Ca<sub>3</sub>Zr<sub>2</sub>(Fe<sup>+3</sup>O<sub>4</sub>)<sub>2</sub>(SiO<sub>4</sub>) || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Kimzeyite]] || Ca<sub>3</sub>Zr<sub>2</sub>(Al<sup>+3</sup>O<sub>4</sub>)<sub>2</sub>(SiO<sub>4</sub>) || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Knorringite]] || Mg<sub>3</sub>Cr<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Majorite]] || Mg<sub>3</sub>(Fe<sup>2+</sup>Si)(SiO<sub>4</sub>)<sub>3</sub> || tetragonal || 4/m <br>or 4/mmm || I4<sub>1</sub>/a <br>or I4<sub>1</sub>/acd
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| |[[Menzerite-(Y)]] || Y<sub>2</sub>CaMg<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Momoiite]] || Mn<sup>2+</sup><sub>3</sub>V<sup>3+</sup><sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Morimotoite]] || Ca<sub>3</sub>(Fe<sup>2+</sup>Ti<sup>4+</sup>)(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Pyrope]] || Mg<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Schorlomite]] || Ca<sub>3</sub>Ti<sup>4+</sup><sub>2</sub>(Fe<sup>3+</sup>O<sub>4</sub>)<sub>2</sub>(SiO<sub>4</sub>) || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |-
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| | [[Spessartine]] || Mn<sup>2+</sup><sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| | [[Toturite]] || Ca<sub>3</sub>Sn<sub>2</sub>(Fe<sup>3+</sup>O<sub>4</sub>)<sub>2</sub>(SiO<sub>4</sub>) || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| | [[Uvarovite]] || Ca<sub>3</sub>Cr<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> || isometric || m{{overline|3}}m || Ia{{overline|3}}d
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| |}
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| *References: [[Mindat.org]]; mineral name, chemical formula and space group (American Mineralogist Crystal Structure Database) of the IMA Database of Mineral Properties/ RRUFF Project, Univ. of Arizona, was preferred most of the time. Minor components in formulae have been left out to highlight the dominant chemical endmember that defines each species.
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| ==Synthetic garnets== | |
| The crystallographic structure of garnets has been expanded from the prototype to include chemicals with the general formula ''A''<sub>3</sub>''B''<sub>2</sub>(''C'' O<sub>4</sub>)<sub>3</sub>. Besides silicon, a large number of elements have been put on the ''C'' site, including {{Germanium}}, {{Gallium}}, {{Aluminum}}, {{Vanadium}} and {{Iron}}.<ref>S. Geller ''Crystal chemistry of the garnets'' Zeitschrift für Kristallographie, '''125'''(125), pp. 1–47 (1967) {{doi|10.1524/zkri.1967.125.125.1}}</ref>
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| [[Yttrium aluminium garnet]] (YAG), Y<sub>3</sub>Al<sub>2</sub>(AlO<sub>4</sub>)<sub>3</sub>, is used for [[Chemical synthesis|synthetic]] gemstones. Due to its fairly high refractive index, YAG was used as a diamond simulant in the 1970s until the methods of producing the more advanced simulant [[cubic zirconia]] in commercial quantities were developed. When doped with [[neodymium]] (Nd<sup>3+</sup>), these YAl-garnets may be used as the lasing medium in [[Nd-YAG laser|lasers]].
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| Interesting magnetic properties arise when the appropriate elements are used. In [[yttrium iron garnet]] (YIG), {{Yttrium}}<sub>3</sub>{{Iron}}<sub>2</sub>(Fe{{Oxygen}}<sub>4</sub>)<sub>3</sub>, the five iron(III) ions occupy two [[octahedral]] and three [[tetrahedral]] sites, with the yttrium(III) ions coordinated by eight oxygen ions in an irregular cube. The iron ions in the two coordination sites exhibit different [[spin (physics)|spins]], resulting in [[magnetic]] behaviour. YIG is a [[Ferrimagnetism|ferrimagnetic]] material having a [[Curie point|Curie temperature]] of 550 [[Kelvin|K]].
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| Another example is [[gadolinium gallium garnet]], {{Gadolinium}}<sub>3</sub>{{Gallium}}<sub>2</sub>(GaO<sub>4</sub>)<sub>3</sub> which is synthesized for use as a substrate for liquid-phase epitaxy of magnetic garnet films for [[bubble memory]] and [[Photomagnetism|magneto-optical]] applications.
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| == Geological importance of garnet == | |
| {{unreferenced section|date=January 2012}}
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| [[File:Garnet var. Spessartine, Putian City, Putian Prefecture, Fujian Province, China.jpg|thumb|Garnet var. Spessartine, Putian City, Putian Prefecture, Fujian Province, China]]
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| The Garnet group is a key mineral in interpreting the genesis of many igneous and metamorphic rocks via [[geothermobarometry]]. [[Diffusion]] of elements is relatively slow in garnet compared to rates in many other minerals, and garnets are also relatively resistant to [[metasomatism|alteration]]. Hence, individual garnets commonly preserve compositional zonations that are used to interpret the temperature-time histories of the rocks in which they grew. Garnet grains that lack compositional zonation commonly are interpreted as having been homogenized by diffusion, and the inferred homogenization also has implications for the temperature-time history of the host rock.
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| Garnets are also useful in defining [[metamorphism|metamorphic facies]] of rocks. For instance, eclogite can be defined as a rock of [[basalt]] composition, but mainly consisting of garnet and [[omphacite]]. Pyrope-rich garnet is restricted to relatively high-pressure metamorphic rocks, such as those in the lower [[crust (geology)|crust]] and in the Earth's mantle. Peridotite may contain [[plagioclase]], or aluminium-rich spinel, or pyrope-rich garnet, and the presence of each of the three minerals defines a pressure-temperature range in which the mineral could equilibrate with [[olivine]] plus [[pyroxene]]: the three are listed in order of increasing pressure for stability of the peridotite mineral assemblage{{vague|date=January 2012}}. Hence, garnet peridotite must have been formed at great depth in the earth. [[Xenolith]]s of garnet peridotite have been carried up from depths of 100 km and greater by kimberlite, and garnets from such disaggegated xenoliths are used as a kimberlite indicator minerals in diamond prospecting. At depths of about 300 to 400 km and greater, a pyroxene component is dissolved in garnet, by the substitution of (Mg,Fe) plus Si for 2Al in the octahedral (Y) site in the garnet structure, creating unusually silica-rich garnets that have solid solution towards majorite. Such silica-rich garnets have been identified as inclusions within diamonds.
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| ==Uses of garnets==
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| [[File:Flickr - portableantiquities - Hilt Fitting.jpg|thumb|c. 8th century AD, [[Anglo-Saxon art|Anglo-Saxon]] sword hilt fitting – gold with gemstone inlay of [[garnet cloisonné]]. From the [[Staffordshire Hoard]], found in 2009, and not fully cleaned.]]
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| [[File:garnet.uvarovite.500pix.jpg|thumb|Pendant in uvarovite, a rare bright-green garnet.]]
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| ===Gemstones===
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| Red garnets were the most commonly used gemstones in the [[Late Antique]] [[Ancient Rome|Roman]] world, and the [[Migration Period art]] of the "[[barbarian]]" peoples who took over the territory of the [[Western Roman Empire]]. They were especially used inlaid in gold cells in the [[cloisonné]] technique, a style often just called garnet cloisonné, found from [[Anglo-Saxon]] England, as at [[Sutton Hoo]], to the [[Black Sea]].
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| Pure crystals of garnet are still used as gemstones. The gemstone varieties occur in shades of green, red, yellow, and orange.<ref>[http://www.geo.utexas.edu/courses/347k/redesign/gem_notes/garnet/garnet_main.htm Geological Sciences at University of Texas, Austin]. Geo.utexas.edu. Retrieved on 2011-12-25.</ref> In the [[USA]] it is known as the [[birthstone]] for January.<ref name="GRG">[[Gemological Institute of America]], ''GIA Gem Reference Guide'' 1995, ISBN 0-87311-019-6</ref> It is the [[List of U.S. state minerals, rocks, stones and gemstones|state mineral]] of [[Connecticut]],<ref>[http://www.sots.ct.gov/sots/cwp/view.asp?A=3188&QUESTION_ID=392608 State of Connecticut, Sites º Seals º Symbols]; ''Connecticut State Register & Manual''; retrieved on December 20, 2008</ref> [[New York's]] gemstone,<ref>[http://www.statesymbolsusa.org/New_York/gem_garnet.html New York State Gem]; ''State Symbols USA''; retrieved on October 12, 2007</ref> and star garnet (garnet with [[rutile]] asterisms) is the state gemstone of [[Idaho]].<ref>[http://web.archive.org/web/20100630201842/http://gov.idaho.gov/fyi/symbols/symbols_index.html Idaho state symbols]. idaho.gov</ref>
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| ===Industrial uses===
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| Garnet sand is a good [[abrasive]], and a common replacement for silica sand in sand blasting. Alluvial garnet grains which are rounder are more suitable for such blasting treatments. Mixed with very high pressure water, garnet is used to cut [[steel]] and other materials in [[Water jet cutter|water jets]]. For water jet cutting, garnet extracted from hard rock is suitable since it is more angular in form, therefore more efficient in cutting.
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| Garnet paper is favored by cabinetmakers for finishing bare wood.<ref>{{cite book |last=Joyce |first=Ernest |editor-first=Alan |editor-last=Peters |editor-link=Alan Peters |title=The Technique of Furniture Making |edition=4th |year=1987 |origyear=1970 |publisher=Batsford |location=London |isbn=071344407X }}</ref>
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| Garnet sand is also used for [[water filtration]] media.
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| As an abrasive garnet can be broadly divided in two categories; blasting grade and water jet grade. The garnet, as it is mined and collected, is crushed to finer grains; all pieces which are larger than 60 mesh (250 micrometers) are normally used for sand blasting. The pieces between 60 mesh (250 micrometers) and 200 mesh (74 micrometers) are normally used for water jet cutting. The remaining garnet pieces that are finer than 200 mesh (74 micrometers) are used for glass polishing and lapping. Regardless of the application, the larger grain sizes are used for faster work and the smaller ones are used for finer finishes.
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| There are different kinds of abrasive garnets which can be divided based on their origin. The largest source of abrasive garnet today is
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| garnet-rich beach sand which is quite abundant on [[India]]n and [[Australia]]n coasts and the main producers today are Australia and India.<ref>{{cite book|last=Briggs |first=J. |title=The Abrasives Industry in Europe and North America|year=2007 |publisher=Materials Technology Publications |isbn=1-871677-52-1}}</ref>
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| This material is particularly popular due to its consistent supplies, huge quantities and clean material. The common problems with this material are the presence of ilmenite and chloride compounds. Since the material has been naturally crushed and ground on the beaches for past centuries, the material is normally available in fine sizes only. Most of the garnet at the [[Thoothukudi|Tuticorin]] beach in south India is 80 mesh, and ranges from 56 mesh to 100 mesh size.{{Citation needed|date=November 2008}}
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| ''River garnet'' is particularly abundant in Australia. The river sand garnet occurs as a [[placer deposit]].{{Citation needed|date=November 2008}}
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| ''Rock garnet'' is perhaps the garnet type used for the longest period of time. This type of garnet is produced in America, China and western India. These crystals are crushed in mills and then purified by wind blowing, magnetic separation, sieving and, if required, washing. Being freshly crushed, this garnet has the sharpest edges and therefore performs far better than other kinds of garnet. Both the river and the beach garnet suffer from the tumbling effect of hundreds of thousands of years which rounds off the edges.
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| Garnet has been mined in western [[Rajasthan]] in northwestern India for the past 200 years, but mainly for the gemstone grade stones. Abrasive garnet was mainly mined as a secondary product while mining for gem garnets and was used as lapping and polishing media for the glass industries. The host rock of the garnet here is garnetiferous [[mica schist]] and the total percentage of garnet is not more than 7% to 10%,{{Citation needed|date=November 2008}} which makes the material extremely costly and non-economical to extract for non-gemstone applications.
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| ==See also==
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| * [[Tsavorite]]
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| * [[Geology]]
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| * [[Mineral collecting]]
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| * [[Mineral]]
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| * [[Gemstone]]
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| * [[Abrasive blasting]]
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| ==Notes==
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| {{Reflist|group=note}}
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| ==References==
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| {{Reflist|35em}}
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| ==Further reading==
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| *Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., Wiley, ISBN 0-471-80580-7
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| *Color Encyclopedia of Gemstones ISBN 0-442-20333-0
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| ==External links==
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| {{Commons category}}
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| *http://www.gemstonemagnetism.com contains a comprehensive section about garnets and garnet magnetism.
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| *[http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/garnet.html USGS Garnet locations – USA]
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| *http://www.gemstone.org/gem-by-gem/english/garnet.html
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| *http://www.mindat.org/min-10272.html
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| * [http://blogs.loc.gov/law/2012/01/garnets/ Blog post on garnets on the [[Law Library of Congress]]'s blog]
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| {{Jewelry}}
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| [[Category:Gemstones]]
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| [[Category:Abrasives]]
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| [[Category:Magnesium minerals]]
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| [[Category:Symbols of Connecticut]]
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| [[Category:Symbols of Vermont]]
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| [[Category:Cubic minerals]]
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| [[Category:Garnet group|Garnet group]]
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| {{Link GA|zh}}
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