Garnet 37506 225401898 2008-07-13T14:18:03Z Gwernol 266416 Reverted edits by [[Special:Contributions/84.128.238.21|84.128.238.21]] ([[User talk:84.128.238.21|talk]]) to last version by Vsmith {{otheruses}} {{Infobox mineral | name = ''''''Garnet '''''' | category = [[Silicate minerals|nesosilicates]] | boxwidth = | boxbgcolor = | image = GarnetCrystalUSGOV.jpg | caption = | formula = The general formula <!-- -->''X''<sub>3</sub>''Y''<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> | molweight = | color = virtually all colors | habit = rhombic dodecahedra or cubic | system = [[Cubic (crystal system)| Cubic]] | twinning = | cleavage = None | fracture = conchoidal to uneven | mohs = 6.0 - 7.5 | luster = vitreous to resinous | polish = vitreous to subadamantine <ref name="GRG"/> | refractive = 1.72 - 1.94 | opticalprop = Single refractive, often anomalous double refractive <ref name="GRG"/> | birefringence = None | pleochroism = only in certain rare varieties | streak = White | gravity = 3.1 - 4.3 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = | other = | var1 = Pyrope | var1text = Mg<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> | var2 = Almandine | var2text = Fe<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> | var3 = Spessartite | var3text = Mn<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> | var4 = Andradite | var4text = Ca<sub>3</sub>Fe<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> | var5 = Grossular | var5text = Ca<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> | var6 = Uvarovite | var6text = Ca<sub>3</sub>Cr<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> }} '''Garnet''' is a group of minerals that have been used since the [[Bronze Age]] as gemstones and abrasives. Garnets are most often seen in red, but are available in a wide variety of colors spanning the entire spectrum. The name "garnet" comes from the [[Latin language|Latin]] ''granatus'' ("[[grain]]"), possibly a reference to the ''Punica granatum'' ("[[pomegranate]]"), a plant with red seeds similar in shape, size, and color to some garnet crystals. Six common species of garnet are recognized based on their chemical composition. They are [[pyrope]], [[almandine]], [[spessartite]], [[grossular]] (varieties of which are [[hessonite]] or cinnamon-stone and [[tsavorite]]), [[uvarovite]] and [[andradite]]. The garnets make up two solid solution series; 1. pyrope-almandine-spessarite and 2. uvarovite-grossular-andradite. ==Physical properties== ===Properties=== Garnets species are found in many colors including red, orange, yellow, green, blue, purple, brown, 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]] 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]]. Garnet species’s 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]] (glass-like) or resinous (amber-like). ===Crystal structure=== [[Image:Garnet_s.jpg|thumb|right|Molecular model of garnet.]] 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> providing the tetrahedra<ref name=>{{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. ===Hardness=== 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 about 6.5 to 7.5. The harder species, like almandine, are often used for abrasive purposes. ==Garnet group [[Endmember (mineralogy)|endmember]] species== ===Pyralspite garnets - Aluminium in ''Y'' site=== *[[Almandine]]: Fe<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> *[[Pyrope]]: Mg<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> *[[Spessartine]]: [[manganese|Mn]]<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> ====Almandine==== [[Image:Almandine.jpeg|thumb|right|Almandine in gneissic rock]] [[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. ====Pyrope==== [[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 almost black. Transparent pyropes are used as [[gemstone]]s. A variety of pyrope from [[Macon County, North Carolina|Macon County]], [[North Carolina]] is a violet-red shade and has been called ''rhodolite'', from the Greek meaning "a rose." In chemical composition it may be considered as essentially an isomorphous mixture of pyrope and almandite, in the proportion of two parts pyrope to one part almandite. 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. 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. ====Spessartine==== [[Image:Espessartita.jpeg|thumb|right|Spessartine (the yellow mineral)]] [[Spessartine]] or incorrectly 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 a beautiful [[orange (color)|orange]]-yellow is found in [[Madagascar]] (see [[Mandarin garnet]]). Violet-red spessartines are found in [[rhyolite]]s in [[Colorado]] and [[Maine]].. ===Ugrandite group - calcium in ''X'' site=== *[[Andradite]]: Ca<sub>3</sub>Fe<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> *[[Grossular]]: Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> *[[Uvarovite]]: Ca<sub>3</sub>Cr<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> ====Andradite==== [[Image:Granat_(andradyt)_i_diopsydy,_Maroko.jpg|thumb|right|Andradite (the black mineral)]] [[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 melantite (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. ====Grossular==== [[Image:GrossularShades.jpg|thumb|right|Grossular on display at the US [[National Museum of Natural History]].]] [[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 [[metamorphic rock|metamorphosed]] [[limestone]]s with [[vesuvianite]], [[diopside]], [[wollastonite]] and [[wernerite]]. One of the most sought after varieties of gem garnet is the fine green grossular garnet from Kenya and Tanzania called [[tsavorite]]. This garnet was discovered in the 1960s in the Tsavo area of Kenya, from which the gem takes its name. ====Uvarovite==== [[Image:Uwarowit, Rosja.jpg|thumb|Uvarovite]] [[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 [[schist]]s in the [[Ural mountains]] of [[Russia]] and [[Outokumpu, Finland]]. ===Less common species=== *Calcium in ''X'' site **Goldmanite: Ca<sub>3</sub>[[vanadium|V]]<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> **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> **Morimotoite: Ca<sub>3</sub>Ti<sup>4+</sup>Fe<sup>2+</sup>(SiO<sub>4</sub>)<sub>3</sub> **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> *Hydroxide bearing - calcium in ''X'' site **[[Hydrogrossular]]: Ca<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3-x</sub>(OH)<sub>4x</sub> ***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) ***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) *Magnesium or manganese in ''X'' site **[[Knorringite]]: Mg<sub>3</sub>Cr<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> **[[Majorite]]: Mg<sub>3</sub>(Fe,Al,Si)<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> **[[Calderite]]: Mn<sub>3</sub>Fe<sup>3+</sup><sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> ====Knorringite==== [[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. Knorringite 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. ==Synthetic garnets== 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&nbsp;[[Kelvin|K]]. By substituting specific sites with [[rare earth elements]], for example, interesting magnetic properties can be obtained. One example for this is [[gadolinium gallium garnet]], {{Gadolinium}}<sub>3</sub>{{Gallium}}<sub>2</sub>([[Gallium|Ga]]O<sub>4</sub>)<sub>3</sub>, which is synthesized for use in magnetic [[bubble memory]]. [[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]] [[gemstone]]. When doped with [[neodymium]] (Nd<sup>3+</sup>), these YAl-garnets are useful as the lasing medium in [[Nd-YAG laser|lasers]]. == Geological importance of garnet == The Garnet group is a key mineral in interpreting the genesis of many [[igneous rock|igneous]] and [[metamorphic rock]]s 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. 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. 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. ==Uses of garnets== [[Image:garnet.uvarovite.500pix.jpg|thumb|right|upright|Pendant in uvarovite, a rare bright-green garnet.]] Pure crystals of garnet are used as [[gemstone]]s. Garnet sand is a good [[abrasive]], and a common replacement for silica sand in sand blasting. Mixed with very high pressure water, garnet is used to cut steel and other materials in [[Water jet cutter|water jets]]. Garnet sand is also used for [[water filtration]] media. *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 gemstone for the 2nd [[wedding anniversary]]<ref>[http://www.longlocks.com/birthstone-anniversary-color-chart.htm LongLocks HairSticks® Boutique's Birthstones and Anniversary Gemstones Chart]; ''LongLocks HairSticks® Boutique''; retrieved on [[October 4]], [[2007]]</ref> *It is the [[List of U.S. state minerals, rocks, stones and gemstones|state mineral]] of [[Connecticut]].<ref>[http://www.sots.ct.gov/RegisterManual/SectionX/SITESEALSYMB.htm State of Connecticut, Sites º Seals º Symbols]; ''Connecticut State Register & Manual''; retrieved on [[January 4]], [[2007]]</ref> *It is also [[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> ==References== {{commonscat}} {{reflist}} {{refbegin}} *Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., Wiley, ISBN 0-471-80580-7 *Color Encyclopedia of Gemstones ISBN 0-442-20333-0 {{refend}} ==External links== *[http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/garnet.html USGS Garnet locations - USA] *[http://www.gia.edu/gemsandgemology/18578/1913/522/back_issue_article_detail.cfm Garnets from Madagascar with a Color Change of Blue-Green to Purple ] *http://www.gemstone.org/gem-by-gem/english/garnet.html *http://www.mindat.org/min-10272.html {{Jewellery Materials}} [[Category:Gemstones]] [[Category:Magnesium minerals]] [[Category:Nesosilicates]] [[Category:Symbols of Connecticut]] [[Category:Symbols of Vermont]] [[bg:Гранат]] [[ca:Granat]] [[cs:Granát (minerál)]] [[da:Granat (mineral)]] [[de:Granatgruppe]] [[et:Granaadid]] [[es:Granate (mineral)]] [[eo:Grenato]] [[eu:Granate (minerala)]] [[fa:لعل]] [[fr:Grenat]] [[hr:Granati]] [[it:Granato]] [[he:גארנט]] [[ka:გრანატები]] [[lt:Granatas]] [[nl:Granaat (mineraal)]] [[ja:柘榴石]] [[pl:Granat (minerał)]] [[pt:Granada (mineralogia)]] [[ro:Granat]] [[ru:Гранат (минерал)]] [[simple:Garnet]] [[sk:Skupina granátu]] [[fi:Granaatti]] [[sv:Granater]] [[uk:Гранати]] [[zh:石榴石]]