Garnets ( / ˈ ɡ ɑːr n ɪ t / ) are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives .
48-509: 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-spessartine (pyralspite), with the composition range [Mg,Fe,Mn] 3 Al 2 (SiO 4 ) 3 ; and uvarovite-grossular-andradite (ugrandite), with
96-437: A Curie temperature of 550 K . Yttrium iron garnet can be made into YIG spheres , which serve as magnetically tunable filters and resonators for microwave frequencies. Lutetium aluminium garnet (LuAG), Al 5 Lu 3 O 12 , 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
144-519: A mixture can be defined as the distribution of the individual substances that constitute the mixture, called "components". In other words, it is equivalent to quantifying the concentration of each component. Because there are different ways to define the concentration of a component, there are also different ways to define the composition of a mixture. It may be expressed as molar fraction , volume fraction , mass fraction , molality , molarity or normality or mixing ratio . Chemical composition of
192-447: A 2:1 ratio of hydrogen atoms to oxygen atoms. Different types of chemical formulas are used to convey composition information, such as an empirical or molecular formula . Nomenclature can be used to express not only the elements present in a compound but their arrangement within the molecules of the compound. In this way, compounds will have unique names which can describe their elemental composition. The chemical composition of
240-479: A Gore Mountain garnet to obtain a Lu-Hf isochron age of 1046.6 ± 6 Ma. It is therefore concluded 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. Red garnets were
288-657: 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 . Garnets can be chemically altered and most often alter to serpentine, talc , and chlorite . The open-pit Barton Garnet Mine, located at Gore Mountain in the Adirondack Mountains , 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
336-713: A mixture can be represented graphically in plots like ternary plot and quaternary plot. Alabanda Alabanda ( Ancient Greek : Ἀλάβανδα ) or Antiochia of the Chrysaorians was a city of ancient Caria , Anatolia , the site of which is near Doğanyurt, Çine , Aydın Province , Turkey . The city is located in the saddle between two heights. The area is noted for its dark marble and for gemstones that resembled garnets . Stephanus of Byzantium claims that there were two cities named Alabanda (Alabandeus) in Caria, but no other ancient source corroborates this. According to legend,
384-666: A number of other buildings, but excavations have yielded very few inscriptions. The names of some bishops of Alabanda are known because of their participation in church councils. Thus Theodoret was at the Council of Chalcedon in 451, Constantine at the Trullan Council in 692, another Constantine at the Second Council of Nicaea in 787, and John at the Photian Council of Constantinople (879) . The names of two non-orthodox bishops of
432-451: 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 . Andradite is a calcium-iron garnet, Ca 3 Fe 2 (SiO 4 ) 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). The red-brown translucent variety of colophonite
480-604: Is also named 'gomed' in Indian literature and is one of the 9 jewels in Vedic astrology that compose the Navaratna . 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
528-418: Is categorized as vitreous (glass-like) or resinous (amber-like). Garnets are nesosilicates having the general formula X 3 Y 2 ( Si O 4 ) 3 . The X site is usually occupied by divalent cations ( Ca , Mg , Fe , Mn ) and the Y site by trivalent cations ( Al , Fe, Cr ) in an octahedral / tetrahedral framework with [SiO 4 ] occupying the tetrahedra. Garnets are most often found in
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#1732844925208576-426: 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
624-495: 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 meaning inferior. Grossular
672-463: Is found in crystalline marbles and schists in the Ural Mountains of Russia and Outokumpu, Finland . Uvarovite is named for Count Uvaro , a Russian imperial statesman. Knorringite is a magnesium-chromium garnet species with the formula Mg 3 Cr 2 (SiO 4 ) 3 . Pure endmember knorringite never occurs in nature. Pyrope rich in the knorringite component is only formed under high pressure and
720-601: 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 area of Kenya, from which the gem takes its name. Uvarovite is a calcium chromium garnet with the formula Ca 3 Cr 2 (SiO 4 ) 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
768-581: Is manganese aluminium garnet, Mn 3 Al 2 (SiO 4 ) 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 -yellow is found in Madagascar. Violet-red spessartines are found in rhyolites in Colorado and Maine . Blue pyrope–spessartine garnets were discovered in
816-505: Is often found in kimberlites . It is used as an indicator mineral in the search for diamonds . 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 O 4 ) 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), Y 3 Al 2 (AlO 4 ) 3 ,
864-507: 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
912-470: 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 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) , Tb 3 Ga 5 O 12 , is a Faraday rotator material with excellent transparency properties and
960-525: 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 Tuticorin beach in south India is 80 mesh, and ranges from 56 mesh to 100 mesh size. River garnet
1008-494: Is pyrope, which is often found in peridotites and kimberlites , 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 isograds in metamorphic rocks. Compositional zoning and inclusions can mark
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#17328449252081056-426: Is recognized as a partially obsolete name. 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 is a calcium-aluminium garnet with the formula Ca 3 Al 2 (SiO 4 ) 3 , though the calcium may in part be replaced by ferrous iron and the aluminium by ferric iron. The name grossular
1104-764: 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
1152-439: Is the state gemstone of New York , and grossular garnet is the state gemstone of Vermont . 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 jets . For water jet cutting, garnet extracted from hard rock
1200-620: 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 in commercial quantities were developed. When doped with neodymium (Nd), erbium or gadolinium YAG may be used as the lasing medium in Nd:YAG lasers , Er:YAG lasers and Gd:YAG lasers respectively. These doped YAG lasers are used in medical procedures including laser skin resurfacing , dentistry, and ophthalmology. Interesting magnetic properties arise when
1248-475: 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 magnetic field sensors. Another example is gadolinium gallium garnet (GGG) , Gd 3 Ga 2 (GaO 4 ) 3 which is synthesized for use as a substrate for liquid-phase epitaxy of magnetic garnet films for bubble memory and magneto-optical applications. The mineral garnet
1296-506: The dodecahedral 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 {100} and {111} families of planes are depleted. Garnets do not have any cleavage planes, so when they fracture under stress, sharp, irregular ( conchoidal ) pieces are formed. Because
1344-660: 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
1392-622: The Seleucid defeat at the Battle of Magnesia in 190 BC. The Romans occupied the city shortly thereafter. According to Cicero in Greece they worshiped a number of deified human beings, at Alabanda there was Alabandus . In 40 BC, the rebel Quintus Labienus at the head of a Parthian army took the city. After Labienus's garrison was slaughtered by the city's inhabitants, the Parthian army stripped
1440-456: The United States it is known as the birthstone for January. It is also the birthstone of Aquarius and Capricorn in tropical astrology . 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. Almandine garnet is the state mineral of Connecticut , star garnet is the state gemstone of Idaho , garnet
1488-406: 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
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1536-403: The appropriate elements are used. In yttrium iron garnet (YIG), Y 3 Fe 2 (FeO 4 ) 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 spins , resulting in magnetic behavior. YIG is a ferrimagnetic material having
1584-567: 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
1632-487: 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. For gem identification purposes, a pick-up response to a strong neodymium magnet separates garnet from all other natural transparent gemstones commonly used in
1680-515: The city from King Xerxes I (r. 486-465 BC). In the early Seleucid period, the city was part of the Chrysaorian League , a loose federation of nearby cities linked by economic and defensive ties and, perhaps, by ethnic ties. The city was renamed Antiochia of the Chrysaorians in honor of Seleucid king Antiochus III who preserved the city's peace. It was captured by Philip V of Macedon in 201 BC. The name reverted to Alabanda after
1728-515: The city of its treasures. Under the Roman Empire , the city became a conventus ( Pliny , V, xxix, 105) and Strabo reports on its reputation for high-living and decadence. The city minted its own coins down to the mid-third century. During the Byzantine Empire , the city was a created a bishopric . The ruins of Alabanda are 8 km west of Çine and consist of the remains of a theatre and
1776-622: The city was founded by the Carian hero Alabandus . In the Carian language , the name is a combination of the words for horse ala and victory banda . On one occasion, Herodotus mentions Alabanda being located in Phrygia , instead of in Caria, but in fact the same city were meant. Amyntas , son of the Persian official Bubares and grandson of the Macedonian King Amyntas , received control of
1824-537: The composition range Ca 3 [Cr,Al,Fe] 2 (SiO 4 ) 3 . The word garnet comes from the 14th-century Middle English word gernet , meaning 'dark red'. It is borrowed from Old French grenate from Latin granatus, from granum ('grain, seed'). 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. Hessonite garnet
1872-454: The identity, arrangement, and ratio of the chemical elements making up a compound by way of chemical and atomic bonds . Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for water is H 2 O: this means that each molecule of water is constituted by 2 atoms of hydrogen (H) and 1 atom of oxygen (O). The chemical composition of water may be interpreted as
1920-399: 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. Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle (though originally almost any red gemstone
1968-614: 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.% V 2 O 3 ). 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
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2016-731: 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 age lamprophyre at Cedar Mountain in Wyoming . A variety of pyrope from 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
2064-471: 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 (from the Greek pyrōpós meaning "firelike") is red in color and chemically an aluminium silicate with the formula Mg 3 Al 2 (SiO 4 ) 3 , though
2112-693: The most commonly used gemstones in the Late Antique 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
2160-463: 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 eclogites ) commonly contain a pyrope variety. Spessartine or spessartite
2208-461: 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. Chemical composition A chemical composition specifies
2256-400: 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 seven different fractions of
2304-533: 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 3 Al 2 (SiO 4 ) 3 ; the deep red transparent stones are often called precious garnet and are used as gemstones (being
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