Garnets () are a group of

silicate mineral 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 consid ...

s that have been used since the

Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second prin ...

as gemstones and

abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...

s. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different species are pyrope, almandine, spessartine,

grossular Grossular is a calcium-aluminium species of the garnet group of minerals. It has the chemical formula of Ca3Al2(SiO4)3 but the calcium may, in part, be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from t ...

(varieties of which are

hessonite Grossular is a calcium-aluminium species of the garnet group of minerals. It has the chemical formula of Ca3Al2(SiO4)3 but the calcium may, in part, be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from t ...

or cinnamon-stone and

tsavorite Tsavorite or tsavolite is a variety of the garnet group species grossular, a calcium-aluminium garnet with the formula Ca3 Al2 Si3 O12.Gemological Institute of America, ''GIA Gem Reference Guide'' 1995, Trace amounts of vanadium or chromium pro ...

uvarovite Uvarovite is a chromium-bearing garnet group species with the formula: Ca3 Cr2( Si O4)3. It was discovered in 1832 by Germain Henri Hess who named it after Count Sergei Semenovitch Uvarov (1765–1855), a Russian statesman and amateur mineral ...

and andradite. The garnets make up two

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...

series: pyrope-almandine-spessartine (pyralspite), with the composition range ; and uvarovite-grossular-andradite (ugrandite), with the composition range .

Etymology

The word ''garnet'' comes from the 14th-century

Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English ...

word ''gernet'', meaning 'dark red'. It is borrowed from Old French ''grenate'' from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''granatus,'' from ''granum'' ('grain, seed'). This is possibly a reference to ''mela granatum'' or even ''pomum granatum'' ('

pomegranate The pomegranate (''Punica granatum'') is a fruit-bearing deciduous shrub in the family Lythraceae, subfamily Punicoideae, that grows between tall. The pomegranate was originally described throughout the Mediterranean Basin, Mediterranean re ...

', ''Punica granatum''), a plant whose fruits contain abundant and vivid red seed covers ( arils), which are similar in shape, size, and color to some garnet crystals.

Physical properties

Properties

Garnet species are found in every colour, with reddish shades most common. Blue garnets are the rarest and were first reported in the 1990s. Garnet

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 luster is categorized as vitreous (glass-like) or resinous (amber-like).

Crystal structure

Garnets are

nesosilicates 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 consid ...

having the general formula ''X''₃''Y''₂()₃. The ''X'' site is usually occupied by divalent cations ( Ca, Mg, Fe, Mn)²⁺ and the ''Y'' site by trivalent cations ( Al, Fe, Cr)³⁺ in an

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...

tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...

framework with iO₄sup>4− occupying the tetrahedra. Garnets are most often found in the

dodecahedral In geometry, a dodecahedron (Greek , from ''dōdeka'' "twelve" + ''hédra'' "base", "seat" or "face") or duodecahedron is any polyhedron with twelve flat faces. The most familiar dodecahedron is the regular dodecahedron with regular pentagon ...

crystal habit, but are also commonly found in the trapezohedron habit as well as the hexoctahedral habit. They crystallize in the cubic system, having three axes that are all of equal length and perpendicular to each other, but are never actually cubic because, despite being isometric, the and families of planes are depleted. Garnets do not have any cleavage planes, so when they fracture under stress, sharp, irregular ( conchoidal) pieces are formed. File:Pyrope cp.jpg, Crystal structure of pyrope garnet. White spheres are oxygen; black, silicon; blue, aluminium; and red, magnesium. File:Pyrope crystal structure.jpg, Same view, with ion sizes reduced to better show all ions File:Pyrope si.jpg, Silicon ion size exaggerated to emphasize silica tetrahedra

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 6.0 to 7.5. The harder species like almandine are often used for abrasive purposes.

Magnetics used in garnet series identification

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.

Garnet group end member species

Pyralspite garnets – aluminium in ''Y'' site

* Almandine: Fe₃Al₂(SiO₄)₃ * Pyrope: Mg₃Al₂(SiO₄)₃ * Spessartine: Mn₃Al₂(SiO₄)₃
Grossular-ww51a

Almandine

Almandine, sometimes incorrectly called almandite, is the modern gem known as

carbuncle A carbuncle is a cluster of boils caused by bacterial infection, most commonly with ''Staphylococcus aureus'' or ''Streptococcus pyogenes''. The presence of a carbuncle is a sign that the immune system is active and fighting the infection. The ...

(though originally almost any red gemstone was known by this name). The term "carbuncle" is derived from the

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 Fe₃Al₂(SiO₄)₃; 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 rocks like mica schists, associated with minerals such as staurolite,

kyanite Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks gener ...

andalusite Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. This mineral was called andalousite by Delamétehrie, who thought it came from Andalusia, Spain. It soon became clear that it was a locality error, and that the spe ...

, and others. Almandine has nicknames of Oriental garnet, almandine ruby, and carbuncle.

Pyrope

Pyrope (from the Greek ''pyrōpós'' meaning "firelike") is red in color and chemically an aluminium silicate with the formula Mg₃Al₂(SiO₄)₃, 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 Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of S ...

s in

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

, from the Bishop Conglomerate and in a Tertiary age lamprophyre at Cedar Mountain in Wyoming. A variety of pyrope from Macon County,

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and ...

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 misnomers; ''Cape ruby'', ''Arizona ruby'', ''California ruby'', ''Rocky Mountain ruby'', and ''Bohemian ruby'' from the Czech Republic. Pyrope is an indicator mineral for high-pressure rocks. Mantle-derived rocks ( peridotites and

eclogite Eclogite () is a metamorphic rock containing garnet (almandine- pyrope) hosted in a matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, ...

s) commonly contain a pyrope variety.

Spessartine

Spessartine or spessartite is manganese aluminium garnet, Mn₃Al₂(SiO₄)₃. Its name is derived from

Spessart Spessart is a '' Mittelgebirge'', a range of low wooded mountains, in the States of Bavaria and Hesse in Germany. It is bordered by the Vogelsberg, Rhön and Odenwald. The highest elevation is the Geiersberg at 586 metres above sea level. Ety ...

Bavaria Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total lan ...

. It occurs most often in

skarn Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate mineral ...

s, granite pegmatite and allied rock types, and in certain low grade metamorphic

phyllite Phyllite ( ) is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. It is primarily compo ...

s. Spessartine of an

orange Orange most often refers to: *Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis'' ** Orange blossom, its fragrant flower *Orange (colour), from the color of an orange, occurs between red and yellow in the visible spectrum * ...

-yellow is found in Madagascar. Violet-red spessartines are found in rhyolites in

Pyrope–spessartine (blue garnet or color-change garnet)

Blue pyrope–spessartine garnets were discovered in the late 1990s in Bekily, Madagascar. This type has also been found in parts of the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

, Russia, Kenya,

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

, and Turkey. It changes color from blue-green to purple depending on the

color temperature Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...

of viewing light, as a result of the relatively high amounts of vanadium (about 1 wt.% V₂O₃). 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. This is the rarest type of garnet. Because of its color-changing quality, this kind of garnet resembles alexandrite.

Ugrandite group – calcium in ''X'' site

* Andradite: Ca₃Fe₂(SiO₄)₃ *

Grossular Grossular is a calcium-aluminium species of the garnet group of minerals. It has the chemical formula of Ca3Al2(SiO4)3 but the calcium may, in part, be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from t ...

: Ca₃Al₂(SiO₄)₃ *

Uvarovite Uvarovite is a chromium-bearing garnet group species with the formula: Ca3 Cr2( Si O4)3. It was discovered in 1832 by Germain Henri Hess who named it after Count Sergei Semenovitch Uvarov (1765–1855), a Russian statesman and amateur mineral ...

: Ca₃Cr₂(SiO₄)₃

Andradite

Andradite is a calcium-iron garnet, Ca₃Fe₂(SiO₄)₃, is of variable composition and may be red, yellow, brown, green or black. The recognized varieties are demantoid (green),

melanite Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12. Andradite includes three varieties: * ''Melanite'': Black in color, referred to as "titanian andradite". and topazolite (yellow or green). Andradite is found in

s and in deep-seated

igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma o ...

s like syenite as well as serpentines and

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 ...

s. Demantoid is one of the most prized of garnet varieties.

Grossular

Grossular is a calcium-aluminium garnet with the formula Ca₃Al₂(SiO₄)₃, though the calcium may in part be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the 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 Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

meaning inferior. Grossular is found in skarns, contact metamorphosed limestones with

vesuvianite Vesuvianite, also known as idocrase, is a green, brown, yellow, or blue silicate mineral. Vesuvianite occurs as tetragonal crystals in skarn deposits and limestones that have been subjected to contact metamorphism. It was first discovered within ...

diopside Diopside is a monoclinic pyroxene mineral with composition . It forms complete solid solution series with hedenbergite () and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull ...

wollastonite Wollastonite is a calcium inosilicate mineral ( Ca Si O3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure limestone or dolomite is subjected to high temperature ...

and wernerite. Grossular garnet from Kenya and

has been called tsavorite. Tsavorite was first described in the 1960s in the

Tsavo Tsavo is a region of Kenya located at the crossing of the Uganda Railway over the Tsavo River, close to where it meets the Athi-Galana-Sabaki River. Two national parks, Tsavo East and Tsavo West are located in the area. The meaning of the w ...

area of Kenya, from which the gem takes its name.

Uvarovite

Uvarovite is a calcium chromium garnet with the formula Ca₃Cr₂(SiO₄)₃. 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 marbles and schists in the Ural mountains of Russia and

Outokumpu, Finland Outokumpu is a List of cities and towns in Finland, town and municipalities of Finland, municipality of Finland. It is located in the North Karelia regions of Finland, region, west of Joensuu and east of Kuopio. The municipality has a population ...

. Uvarovite is named for Count Uvaro, a Russian imperial statesman.

Less common species

*Calcium in ''X'' site ** Goldmanite: **Kimzeyite: **Morimotoite: **Schorlomite: *Hydroxide bearing – calcium in ''X'' site ** Hydrogrossular: ***Hibschite: (where x is between 0.2 and 1.5) ***Katoite: (where x is greater than 1.5) *Magnesium or manganese in ''X'' site ** Knorringite: ** Majorite: ** Calderite:

Knorringite

Knorringite is a magnesium-chromium garnet species with the formula Mg₃Cr₂(SiO₄)₃. Pure

endmember An endmember (also end-member or end member) in mineralogy is a mineral that is at the extreme end of a mineral series in terms of purity of its chemical composition. Minerals often can be described as solid solutions with varying compositions of ...

knorringite never occurs in nature. Pyrope rich in the knorringite component is only formed under high pressure and is often found in

s. It is used as an indicator mineral in the search for diamonds.

Garnet structural group

*Formula: X₃Z₂(TO₄)₃ (X = Ca, Fe, etc., Z = Al, Cr, etc., T = Si, As, V, Fe, Al) **All are cubic or strongly pseudocubic. *IMA/CNMNC – Nickel-Strunz – Mineral subclass: 09.A Nesosilicate ** Nickel-Strunz classification: 09.AD.25 *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.

Synthetic garnets

Also known as rare-earth garnets. The crystallographic structure of garnets has been expanded from the prototype to include chemicals with the general formula ''A''₃''B''₂(''C''O₄)₃. Besides silicon, a large number of elements have been put on the ''C'' site, including germanium, gallium, aluminum, vanadium and

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

Yttrium aluminium garnet Yttrium aluminium garnet (YAG, Y3 Al5 O12) is a synthetic crystalline material of the garnet group. It is a cubic yttrium aluminium oxide phase, with other examples being YAlO3 (YAP) in a hexagonal or an orthorhombic, perovskite-like form, and ...

(YAG), Y₃Al₂(AlO₄)₃, is used for 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 Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirco ...

in commercial quantities were developed. When doped with neodymium (Nd³⁺), YAG may be used as the lasing medium in Nd:YAG lasers. When doped with erbium, it can be used as the lasing medium in Er:YAG lasers. When doped with

gadolinium Gadolinium is a chemical element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white metal when oxidation is removed. It is only slightly malleable and is a ductile rare-earth element. Gadolinium reacts with atmospheric oxygen ...

, it can be used as the lasing medium in Gd:YAG lasers. These doped YAG lasers are used in medical procedures including laser skin resurfacing, dentistry, and ophthalmology. Interesting magnetic properties arise when the appropriate elements are used. In

yttrium iron garnet Yttrium iron garnet (YIG) is a kind of synthetic garnet, with chemical composition , or Y3Fe5O12. It is a ferrimagnetic material with a Curie temperature of 560 K. YIG may also be known as yttrium ferrite garnet, or as iron yttrium oxide or ...

(YIG), Y₃Fe₂(FeO₄)₃, the five iron(III) ions occupy two

and three

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 spins, resulting in magnetic behavior. YIG is a

ferrimagnetic A ferrimagnetic material is a material that has populations of atoms with opposing magnetic moments, as in antiferromagnetism, but these moments are unequal in magnitude so a spontaneous magnetization remains. This can for example occur when ...

material having a

Curie temperature In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cur ...

of 550 K. Yttrium iron garnet can be made into

YIG sphere Yttrium iron garnet spheres (YIG spheres) serve as magnetically tunable filters and resonators for microwave frequencies. YIG filters are used for their high Q factors, typically between 100 and 200. A sphere made from a single crystal of sy ...

s, which serve as magnetically tunable filters and resonators for microwave frequencies. Lutetium aluminium garnet (LuAG), , is an inorganic compound with a unique crystal structure primarily known for its use in high-efficiency laser devices. LuAG is also useful in the synthesis of

transparent ceramics Many ceramic materials, both glassy and crystalline, have found use as optically transparent materials in various forms from bulk solid-state components to high surface area forms such as thin films, coatings, and fibers. Such devices have found ...

. LuAG is particularly favored over other crystals for its high density and thermal conductivity; it has a relatively small

lattice constant A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has o ...

in comparison to the other

rare-earth The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silve ...

garnets, which results in a higher density producing a crystal field with narrower linewidths and greater energy level splitting in absorption and emission. Terbium gallium garnet (TGG), , is a Faraday rotator material with excellent transparency properties and is very resistant to laser damage. TGG can be used in

optical isolator An optical isolator, or optical diode, is an optical component which allows the transmission of light in only one direction. It is typically used to prevent unwanted feedback into an optical oscillator, such as a laser cavity. The operation ...

s for laser systems, in

optical circulator An optical circulator is a three- or four-port optical device designed such that light entering any port exits from the next. This means that if light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to t ...

s for fiber optic systems, in optical modulators, and in current and magnetic field sensors. Another example is gadolinium gallium garnet (GGG), which is synthesized for use as a substrate for liquid-phase epitaxy of magnetic garnet films for

bubble memory Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as ''bubbles'' or ''domains'', each storing one bit of data. The material is arranged to form a series o ...

and

magneto-optical A magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon a magneto-optical disc. Both 130 mm (5.25 in) and 90 mm (3.5 in) form factors exist. In 1983, just a year after the introduct ...

applications.

Geological importance

The mineral garnet is commonly found in metamorphic and to a lesser extent, igneous rocks. Most natural garnets are compositionally zoned and contain inclusions. Its crystal lattice structure is stable at high pressures and temperatures and is thus found in green-schist facies metamorphic rocks including gneiss, hornblende schist, and mica schist. The composition that is stable at the pressure and temperature conditions of Earth's mantle is pyrope, which is often found in peridotites and

s, as well as the serpentines that form from them. Garnets are unique in that they can record the pressures and temperatures of peak metamorphism and are used as geobarometers and geothermometers in the study of geothermobarometry which determines "P-T Paths", Pressure-Temperature Paths. Garnets are used as an index mineral in the delineation of

isograd __NOTOC__ An isograd is a concept used in the study of metamorphic rocks. The metamorphic grade of such a rock is a rough measure of the degree of metamorphism it has undergone, as characterised by the presence of certain index minerals. An isogr ...

s in metamorphic rocks. Compositional zoning and inclusions can mark the change from growth of the crystals at low temperatures to higher temperatures. Garnets that are not compositionally zoned more than likely experienced ultra high temperatures (above 700 °C) that led to diffusion of major elements within the crystal lattice, effectively homogenizing the crystal or they were never zoned. Garnets can also form metamorphic textures that can help interpret structural histories. In addition to being used to devolve conditions of metamorphism, garnets can be used to date certain geologic events. Garnet has been developed as a U-Pb geochronometer, to date the age of crystallization as well as a thermochronometer in the (U-Th)/He system to date timing of cooling below a

closure temperature In radiometric dating, closure temperature or blocking temperature refers to the temperature of a system, such as a mineral, at the time given by its radiometric date. In physical terms, the closure temperature is the temperature at which a syste ...

. Garnets can be chemically altered and most often alter to serpentine,

talc Talc, or talcum, is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent a ...

, and chlorite.

Uses

Flickr - portableantiquities - Hilt Fitting

Gemstones

Red garnets were the most commonly used gemstones in the Late Antique Roman world, and the

Migration Period art Migration Period art denotes the artwork of the Germanic peoples during the Migration period (c. 300 – 900). It includes the Migration art of the Germanic tribes on the continent, as well the start of the Insular art or Hiberno-Saxon art of the ...

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 Cloisonné () is an ancient technique for decorating metalwork objects with colored material held in place or separated by metal strips or wire, normally of gold. In recent centuries, vitreous enamel has been used, but inlays of cut gemstones, ...

technique, a style often just called garnet cloisonné, found from Anglo-Saxon England, as at Sutton Hoo, to the Black Sea. Thousands of Tamraparniyan gold, silver and red garnet shipments were made in the old world, including to Rome, Greece, the Middle East, Serica and Anglo Saxons; recent findings such as the Staffordshire Hoard and the pendant of the Winfarthing Woman skeleton of Norfolk confirm an established gem trade route with South India and Tamraparni (ancient Sri Lanka), known from antiquity for its production of gemstones. Pure crystals of garnet are still used as gemstones. The gemstone varieties occur in shades of green, red, yellow, and orange. In the US it is known as the birthstone for January.Gemological Institute of America, ''GIA Gem Reference Guide'' 1995, The garnet family is one of the most complex in the gem world. It is not a single species, but is composed of multiple species and varieties. It is the List of U.S. state minerals, rocks, stones and gemstones, state mineral of Connecticut, New York (state), New York's gemstone, and star garnet (garnet with rutile asterisms) is the state gemstone of Idaho.

Industrial uses

Garnet sand is a good

, 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. Garnet paper is favored by cabinetmakers for finishing bare wood. Garnet sand is also used for water filtration media. As an abrasive, garnet can be broadly divided into 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. There are different kinds of abrasive garnets which can be divided based on their origin. The largest source of abrasive garnet today is garnet-rich beach sand which is quite abundant on Indian and Australian coasts and the main producers today are Australia and India. 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. ''River garnet'' is particularly abundant in Australia. The river sand garnet occurs as a placer deposit. ''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. Gore Mountain Garnet from Warren County, New York, USA is a significant source of rock garnet for use as an industrial abrasive.

Cultural significance

Garnet is the birthstone of January. It is also the birthstone of Aquarius (astrology), Aquarius and Capricorn (astrology), Capricorn in tropical astrology. In Persia this birth gem was considered a talisman from nature's forces like storm and lightning. It was widely accepted that garnet could signal approaching danger by turning pale.

United States

Garnet is New York State's official gemstone, Connecticut has almandine garnet as its state gemstone, Idaho has star garnet as its state gemstone, and Vermont has

garnet as its state gemstone. Since 2003 New York State has ranked first in industrial garnet-production in the United States. Since there are just a few companies that account for all U.S. industrial garnet production, published detailed production statistics for New York State are not available. However, generally speaking, Barton Mines in Warren County is the largest U.S. garnet producer.

Collections

The New York State Museum in Albany, NY houses specimens from significant sites across the state, including 93 mineral species from the Balmat-Edwards mining district in St. Lawrence, super garnets from the Barton Mine in the Adirondack Mountains, and Herkimer diamonds from Herkimer County, New York

Oldest garnet mine

The largest garnet mine in the world is located Near North Creek New York and is operated by Barton Mines Corporation who supplies about 90% of the world's garnet. Barton Mines Corporation is the first and oldest industrial garnet mining operation in the world and the second oldest continuous mining operation in the United States under the same management and mining the same product throughout its history. The Gore Mountain Mine of the Barton Mines Corporation was first mined under the direction of H. H. Barton, Sr. in 1878 to produce garnet as the primary product.

Largest garnet crystal

The open-pit Barton Garnet Mine, located at Gore Mountain in the Adirondack Highlands, yields the world's largest single crystals of garnet; diameters range from 5 to 35 cm and commonly average 10–18 cm. Gore Mountain garnets are unique in many respects, and considerable effort has been made to determine the timing of garnet growth. The first dating was that of Basu et al. (1989), who used plagioclase-hornblende-garnet to produce a Sm/Nd isochron that yielded an age of 1059 ± 19 Ma. Mezger et al. (1992) conducted their own Sm/Nd investigation using hornblende and the drilled core of a 50 cm garnet to produce an isochron age of 1051 ± 4 Ma. Connelly (2006) utilized 7 different fractions of a Gore Mountain garnet to obtain a Lu-Hf isochron age of 1046.6 ± 6 Ma. We therefore conclude with confidence that the garnets formed at 1049 ± 5 Ma, the average of the three determinations. This is also the local age of peak metamorphism in the 1090–1040 Ma Ottawan phase of the Grenvillian orogeny and serves as a critical data point in ascertaining the evolution of the megacrystic garnet deposits.

References

External links

*http://www.gemstonemagnetism.com contains a comprehensive section about garnets and garnet magnetism.
USGS Garnet locations – USA
*http://gemstone.org/education/gem-by-gem/154-garnet *http://www.mindat.org/min-10272.html
Blog post on garnets
on the Law Library of Congress's blog *https://www.birthstone.guide/garnet-birthstone-meaning Garnet birthstone stories {{Authority control Magnesium minerals Symbols of Connecticut Symbols of Vermont Cubic minerals Minerals in space group 230 Garnet group, * Garnet gemstones, * Industrial minerals