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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
The mineral pyrope is a member of the garnet group. Pyrope is the only member of the garnet family to always display red colouration in natural samples, and it is from this characteristic that it gets its name: from the Greek for ''fire'' and ''e ...
, almandine, spessartine
Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3.Gemological Institute of America, ''GIA Gem Reference Guide'' 1995, This mineral is sometimes mistakenly referred to as ''spessartite''.
Spessartine's name is a ...
, 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
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". This is possibly a reference to ''mela granatum'' or even ''pomum granatum'' ('pomegranate', ''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.
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).
Garnets are Silicate minerals#Nesosilicates or Isosilicates, nesosilicates having the general formula ''X''3''Y''2()3. The ''X'' site is usually occupied by divalent cations (calcium, Ca, magnesium, Mg, iron, Fe, manganese, Mn)2+ and the ''Y'' site by trivalent cations (aluminium, Al, Fe, chromium, Cr)3+ in an octahedron, octahedral/tetrahedron, tetrahedral framework with [SiO4]4− occupying the tetrahedra. Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit as well as the Hexoctahedron, hexoctahedral habit. They crystallize in the Cubic (crystal system), 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 (crystal), 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
Almandine, sometimes incorrectly called almandite, is the modern gem known as Carbuncle (gemstone), 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 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, andalusite, and others. Almandine has nicknames of Oriental garnet, almandine ruby, and carbuncle.
Spessartine or spessartite is manganese aluminium garnet, Mn3Al2(SiO4)3. Its name is derived from Spessart in Bavaria. It occurs most often in skarns, granite pegmatite and allied rock types, and in certain low grade metamorphic phyllites. Spessartine of an orange (colour), orange-yellow is found in Madagascar. Violet-red spessartines are found in rhyolites in Colorado
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 kimberlites, as well as the Serpentine subgroup, 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 isograds 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 Geochronometry, geochronometer, to date the age of crystallization as well as a Thermochronology, thermochronometer in the (U-Th)/He system to date timing of cooling below a closure temperature.
Garnets can be chemically altered and most often alter to serpentine, talc, and Chlorite group, chlorite.
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
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 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).
Crystal structure
Garnets are Silicate minerals#Nesosilicates or Isosilicates, nesosilicates having the general formula ''X''3''Y''2()3. The ''X'' site is usually occupied by divalent cations (calcium, Ca, magnesium, Mg, iron, Fe, manganese, Mn)2+ and the ''Y'' site by trivalent cations (aluminium, Al, Fe, chromium, Cr)3+ in an octahedron, octahedral/tetrahedron, tetrahedral framework with [SiO4]4− occupying the tetrahedra. Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit as well as the Hexoctahedron, hexoctahedral habit. They crystallize in the Cubic (crystal system), 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 (crystal), cleavage planes, so when they fracture under stress, sharp, irregular (conchoidal) 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 mineral hardness, 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: manganese, Mn3Al2(SiO4)3
Almandine
Almandine, sometimes incorrectly called almandite, is the modern gem known as Carbuncle (gemstone), 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 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, andalusite, 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 kimberlites in Colorado, from the Bishop Conglomerate and in a Tertiary, Tertiary age lamprophyre at Cedar Mountain in Wyoming. 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 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. Earth's mantle, Mantle-derived rocks (peridotites and eclogites) commonly contain a pyrope variety.Spessartine
Spessartine or spessartite is manganese aluminium garnet, Mn3Al2(SiO4)3. Its name is derived from Spessart in Bavaria. It occurs most often in skarns, granite pegmatite and allied rock types, and in certain low grade metamorphic phyllites. Spessartine of an orange (colour), orange-yellow is found in Madagascar. Violet-red spessartines are found in rhyolites in Colorado
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, Russia, Kenya, Tanzania, and Turkey. It changes color from blue-green to purple depending on the color temperature 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 Chrysoberyl#Alexandrite, alexandrite.Ugrandite group – calcium in ''X'' site
*Andradite: Ca3Fe2(SiO4)3 *Grossular: Ca3Al2(SiO4)3 *Uvarovite: Ca3Cr2(SiO4)3Andradite
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 (black), and topazolite (yellow or green). Andradite is found in skarns and in deep-seated igneous rocks like syenite as well as serpentines and greenschists. 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 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 skarns, contact metamorphosed limestones with vesuvianite, diopside, wollastonite and wernerite. Grossular garnet from Kenya and Tanzania has been called tsavorite. Tsavorite was first described in the 1960s in the :Tsavo National Park, Tsavo 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. Uvarovite is named for Sergey Uvarov, 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 knorringite never occurs in nature. Pyrope rich in the knorringite component is only formed under high pressure and is often found in kimberlites. 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 **Strunz classification, 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. Yttrium aluminium garnet (YAG), Y3Al2(AlO4)3, 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 (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, it can be used as the lasing medium in Gadolinium yttrium garnet, 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 (YIG), Y3Fe2(FeO4)3, 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 behavior. YIG is a Ferrimagnetism, ferrimagnetic material having a Curie point, Curie temperature of 550 Kelvin, K. Yttrium iron garnet can be made into YIG spheres, which serve as magnetically tunable Signal processing, 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. LuAG is particularly favored over other crystals for its high density and thermal conductivity; it has a relatively small lattice constant in comparison to the other Rare-earth element, rare-earth 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, 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 isolators for laser systems, in optical circulators for fiber optic systems, in optical modulators, and in current and magnetometer, magnetic field sensors. Another example is gadolinium gallium garnet, gadolinium gallium garnet (GGG), which is synthesized for use as a substrate for liquid-phase epitaxy of magnetic garnet films for bubble memory and Photomagnetism, magneto-optical 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 kimberlites, as well as the Serpentine subgroup, 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 isograds 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 Geochronometry, geochronometer, to date the age of crystallization as well as a Thermochronology, thermochronometer in the (U-Th)/He system to date timing of cooling below a closure temperature.
Garnets can be chemically altered and most often alter to serpentine, talc, and Chlorite group, chlorite.
Uses
Gemstones
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. 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 goodabrasive
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 ...
, 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 hasgrossular
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 ...
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 YorkOldest 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.See also
* Abrasive blastingReferences
Further reading
* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., Wiley, * ''Color Encyclopedia of Gemstones'',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