Last updated
Garnet Andradite20.jpg
Category Nesosilicate
(repeating unit)
The general formula X3Y2(SiO4)3
IMA symbol Grt [1]
Crystal system Isometric
Crystal class
Space group Ia3d
Colorvirtually all colors, blue is rare
Crystal habit Rhombic dodecahedron or cubic
Cleavage Indistinct
Fracture conchoidal to uneven
Mohs scale hardness6.5–7.5
Luster vitreous to resinous
Streak White
Diaphaneity Can form with any diaphaneity, translucent is common
Specific gravity 3.1–4.3
Polish lustervitreous to subadamantine [2]
Optical propertiesSingle refractive, often anomalous double refractive [2]
Refractive index 1.72–1.94
Birefringence None
Pleochroism None
Ultraviolet fluorescence variable
Other characteristicsvariable magnetic attraction
Major varieties

Garnets ( /ˈɡɑːrnɪt/ ) are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.


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]3Al2(SiO4)3; and uvarovite-grossular-andradite (ugrandite), with the composition range Ca3[Cr,Al,Fe]2(SiO4)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'). [3] This is possibly a reference to mela granatum or even pomum granatum ('pomegranate', [4] 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. [5] Hessonite garnet is also named 'gomed' in Indian literature and is one of the 9 jewels in Vedic astrology that compose the Navaratna. [6]

Physical properties


A sample showing the deep red color garnet can exhibit. Garnet.JPG
A sample showing the deep red color garnet can exhibit.

Garnet species are found in every colour, with reddish shades most common. Blue garnets are the rarest and were first reported in the 1990s. [7] [8] [9] [10]

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 is categorized as vitreous (glass-like) or resinous (amber-like). [3]

Crystal structure

Garnets are nesosilicates having the general formula X3Y2( Si O
)3. The X site is usually occupied by divalent cations (Ca, Mg, Fe, Mn)2+ and the Y site by trivalent cations (Al 3+, Fe3+, Cr 3+) in an octahedral/tetrahedral framework with [SiO4]4− occupying the tetrahedra. [11] Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit as well as the hexoctahedral habit. [3] 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. [3] Garnets do not have any cleavage planes, so when they fracture under stress, sharp, irregular (conchoidal) pieces are formed. [12]


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. [13] The harder species like almandine are often used for abrasive purposes. [14]

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. [15]

Garnet group end member species

Pyralspite garnets – aluminium in Y site


Almandine in metamorphic rock Almandine.jpeg
Almandine in metamorphic rock

Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle (though originally almost any red gemstone was known by this name). [16] 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). [17] Almandine occurs in metamorphic rocks like mica schists, associated with minerals such as staurolite, kyanite, andalusite, and others. [18] Almandine has nicknames of Oriental garnet, [19] almandine ruby, and carbuncle. [16]


Pyrope (from the Greek pyrōpós meaning "firelike") [3] 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 age lamprophyre at Cedar Mountain in Wyoming. [20]

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 the proportion of two parts pyrope to one part almandine. [21] Pyrope has tradenames some of which are misnomers; Cape ruby, Arizona ruby, California ruby, Rocky Mountain ruby, and Bohemian ruby from the Czech Republic. [16]

Pyrope is an indicator mineral for high-pressure rocks. Mantle-derived rocks (peridotites and eclogites) commonly contain a pyrope variety. [22]


Spessartine (the reddish mineral) Espessartita.jpeg
Spessartine (the reddish mineral)

Spessartine or spessartite is manganese aluminium garnet, Mn3Al2(SiO4)3. Its name is derived from Spessart in Bavaria. [3] It occurs most often in skarns, [3] granite pegmatite and allied rock types, [23] and in certain low grade metamorphic phyllites. Spessartine of an orange-yellow is found in Madagascar. [24] Violet-red spessartines are found in rhyolites in Colorado [21] and Maine.[ citation needed ]

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). [9]

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. [25]

This is the rarest type of garnet. Because of its color-changing quality, this kind of garnet resembles alexandrite. [26]

Ugrandite group – calcium in X site


Andradite is a calcium-iron garnet, Ca3Fe2(SiO4)3, is of variable composition and may be red, yellow, brown, green or black. [3] The recognized varieties are demantoid (green), melanite (black), [3] and topazolite (yellow or green). Andradite is found in skarns [3] and in deep-seated igneous rocks like syenite [27] as well as serpentines [28] and greenschists. [29] Demantoid is one of the most prized of garnet varieties. [30]


Grossular garnet from Quebec, collected by Dr John Hunter in the 18th century, Hunterian Museum, Glasgow Grossular garnet from Quebec, collected by Dr John Hunter in the 18th century, Hunterian Museum, Glasgow.jpg
Grossular garnet from Quebec, collected by Dr John Hunter in the 18th century, Hunterian Museum, Glasgow
Grossular garnets on display at the U.S. National Museum of Natural History. The green gem at right is a type of grossular known as tsavorite. GrossularShades.jpg
Grossular garnets on display at the U.S. National Museum of Natural History. The green gem at right is a type of grossular known as tsavorite.

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. [3] Because of its inferior hardness to zircon, which the yellow crystals resemble, they have also been called hessonite from the Greek meaning inferior. [31] Grossular is found in skarns, [3] 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. [32] [33]


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 Count Uvaro, a Russian imperial statesman. [3]

Less common species


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. [34]

Garnet structural group

Mineral class
Mineral nameFormulaCrystal systemPoint groupSpace group
04 Oxide Bitikleite-(SnAl) Ca3SnSb(AlO4)3isometricm3mIa3d
04 Oxide Bitikleite-(SnFe) Ca3(SnSb5+)(Fe3+O4)3isometricm3mIa3d
04 Oxide Bitikleite-(ZrFe) Ca3SbZr(Fe3+O4)3isometricm3mIa3d
04 Tellurate Yafsoanite Ca3Zn3(Te6+O6)2isometricm3m
or 432
or I4132
08 Arsenate Berzeliite NaCa2Mg2(AsO4)3isometricm3mIa3d
08 Vanadate Palenzonaite NaCa2Mn2+2(VO4)3isometricm3mIa3d
08 Vanadate Schäferite NaCa2Mg2(VO4)3isometricm3mIa3d
Mineral nameFormulaCrystal systemPoint groupSpace group
Almandine Fe2+3Al2(SiO4)3isometricm3mIa3d
Andradite Ca3Fe3+2(SiO4)3isometricm3mIa3d
Calderite Mn+23Fe+32(SiO4)3isometricm3mIa3d
Goldmanite Ca3V3+2(SiO4)3isometricm3mIa3d
Grossular Ca3Al2(SiO4)3isometricm3mIa3d
Henritermierite Ca3Mn3+2(SiO4)2(OH)4tetragonal4/mmmI41/acd
Hibschite Ca3Al2(SiO4)(3−x)(OH)4x (x= 0.2–1.5)isometricm3mIa3d
Katoite Ca3Al2(SiO4)(3−x)(OH)4x (x= 1.5–3)isometricm3mIa3d
Kerimasite Ca3Zr2(Fe+3O4)2(SiO4)isometricm3mIa3d
Kimzeyite Ca3Zr2(Al+3O4)2(SiO4)isometricm3mIa3d
Knorringite Mg3Cr2(SiO4)3isometricm3mIa3d
Majorite Mg3(Fe2+Si)(SiO4)3tetragonal4/m
or 4/mmm
or I41/acd
Menzerite-(Y) Y2CaMg2(SiO4)3isometricm3mIa3d
Momoiite Mn2+3V3+2(SiO4)3isometricm3mIa3d
Morimotoite Ca3(Fe2+Ti4+)(SiO4)3isometricm3mIa3d
Pyrope Mg3Al2(SiO4)3isometricm3mIa3d
Schorlomite Ca3Ti4+2(Fe3+O4)2(SiO4)isometricm3mIa3d
Spessartine Mn2+3Al2(SiO4)3isometricm3mIa3d
Toturite Ca3Sn2(Fe3+O4)2(SiO4)isometricm3mIa3d
Uvarovite Ca3Cr2(SiO4)3isometricm3mIa3d

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 A3B2(CO4)3. Besides silicon, a large number of elements have been put on the C site, including germanium, gallium, aluminum, vanadium and iron. [35]

Yttrium aluminium garnet (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 in commercial quantities were developed. When doped with neodymium (Nd3+), erbium or gadolinium YAG may be used as the lasing medium in Nd:YAG lasers, [36] Er:YAG lasers and Gd:YAG lasers respectively. These doped YAG lasers are used in medical procedures including laser skin resurfacing, dentistry, and ophthalmology. [37] [38] [39]

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 spins, resulting in magnetic behavior. YIG is a ferrimagnetic material having 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. [40]

Lutetium aluminium garnet (LuAG), Al5 Lu3O12, 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. [41] 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 garnets, which results in a higher density producing a crystal field with narrower linewidths and greater energy level splitting in absorption and emission. [42]

Terbium gallium garnet (TGG), Tb3Ga5O12, 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 magnetic field sensors. [43]

Another example is gadolinium gallium garnet (GGG), Gd3Ga2(GaO4)3 which is synthesized for use as a substrate for liquid-phase epitaxy of magnetic garnet films for bubble memory and magneto-optical applications.[ citation needed ]

Geological importance

Main garnet producing countries Grenat.jpg
Main garnet producing countries
Garnet var. Spessartine, Putian City, Putian Prefecture, Fujian Province, China Garnet var. Spessartine, Putian City, Putian Prefecture, Fujian Province, China.jpg
Garnet var. Spessartine, Putian City, Putian Prefecture, Fujian Province, China

The mineral garnet is commonly found in metamorphic and to a lesser extent, igneous rocks. Most natural garnets are compositionally zoned and contain inclusions. [44] 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. [45] 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 serpentines that form from them. [45] 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. [45] Compositional zoning and inclusions can mark the change from growth of the crystals at low temperatures to higher temperatures. [46] 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 [46] or they were never zoned. Garnets can also form metamorphic textures that can help interpret structural histories. [46]

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 [47] as well as a thermochronometer in the (U-Th)/He system [48] to date timing of cooling below a closure temperature.

Garnets can be chemically altered and most often alter to serpentine, talc, and chlorite. [45]


c. 7th century AD, Anglo-Saxon seax hilt fitting - gold with gemstone inlay of garnet cloisonne. From the Staffordshire Hoard, found in 2009, and not fully cleaned Flickr - portableantiquities - Hilt Fitting.jpg
c. 7th century AD, Anglo-Saxon seax hilt fitting – gold with gemstone inlay of garnet cloisonné. From the Staffordshire Hoard, found in 2009, and not fully cleaned
Pendant in uvarovite, a rare bright-green garnet Garnet.uvarovite.500pix.jpg
Pendant in uvarovite, a rare bright-green garnet


Red garnets were 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 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. [49] [50] [51]

Pure crystals of garnet are still used as gemstones. The gemstone varieties occur in shades of green, red, yellow, and orange. [52] In the US it is known as the birthstone for January. [2] 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. [53] It is the state mineral of Connecticut, [54] New York's gemstone, [55] and star garnet (garnet with rutile asterisms) is the state gemstone of Idaho. [56]

Industrial uses

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 is suitable since it is more angular in form, therefore more efficient in cutting. [57]

Garnet paper is favored by cabinetmakers for finishing bare wood. [58]

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.[ citation needed ]

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. [59]

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 Tuticorin beach in south India is 80 mesh, and ranges from 56 mesh to 100 mesh size.[ citation needed ]

River garnet is particularly abundant in Australia. The river sand garnet occurs as a placer deposit. [60]

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. [3]

Cultural significance

Garnet is the birthstone of January. [61] [62] It is also the birthstone of Aquarius and Capricorn in tropical astrology. [63] [64] 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.[ citation needed ]

United States

Garnet is New York State's official gemstone, [65] Connecticut has almandine garnet as its state gemstone, [66] Idaho has star garnet as its state gemstone, [67] and Vermont has grossular garnet as its state gemstone. [68]

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. [69]


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 [70]

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. [71] 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. [71]

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. [72]

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 seven different fractions of 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. [72]

See also

Related Research Articles

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Spinel is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl
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<span class="mw-page-title-main">Peridot</span> Green gem-quality mineral

Peridot, sometimes called chrysolite, is a yellowish-green transparent variety of olivine. Peridot is one of the few gemstones that occur in only one color.

<span class="mw-page-title-main">Zircon</span> Zirconium silicate, a mineral belonging to the group of nesosilicates

Zircon is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is ZrSiO4. An empirical formula showing some of the range of substitution in zircon is (Zr1–y, REEy)(SiO4)1–x(OH)4x–y. Zircon precipitates from silicate melts and has relatively high concentrations of high field strength incompatible elements. For example, hafnium is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system. The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green.

<span class="mw-page-title-main">Kimberlite</span> Igneous rock which sometimes contains diamonds

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 83.5-carat (16.70 g) diamond called the Star of South Africa in 1869 spawned a diamond rush and the digging of the open-pit mine called the Big Hole. Previously, the term kimberlite has been applied to olivine lamproites as Kimberlite II, however this has been in error.

<span class="mw-page-title-main">Sodalite</span> Blue tectosilicate mineral

Sodalite is a tectosilicate mineral with the formula Na
, with royal blue varieties widely used as an ornamental gemstone. Although massive sodalite samples are opaque, crystals are usually transparent to translucent. Sodalite is a member of the sodalite group with hauyne, nosean, lazurite and tugtupite.

<span class="mw-page-title-main">Staurolite</span> Reddish brown to black nesosilicate mineral

Staurolite is a reddish brown to black, mostly opaque, nesosilicate mineral with a white streak. It crystallizes in the monoclinic crystal system, has a Mohs hardness of 7 to 7.5 and the chemical formula: Fe2+2Al9O6(SiO4)4(O,OH)2. Magnesium, zinc and manganese substitute in the iron site and trivalent iron can substitute for aluminium.

<span class="mw-page-title-main">Peridotite</span> Coarse-grained ultramafic igneous rock type

Peridotite ( PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from Earth's mantle, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole.

<span class="mw-page-title-main">Uvarovite</span> Chromium-bearing garnet group

Uvarovite is a chromium-bearing garnet group species with the formula: Ca3Cr2(SiO4)3. It was discovered in 1832 by Germain Henri Hess who named it after Count Sergei Uvarov (1765–1855), a Russian statesman and amateur mineral collector. It is classified in the ugrandite group alongside the other calcium-bearing garnets andradite and grossular.

<span class="mw-page-title-main">Almandine</span> Species of mineral belonging to the garnet group

Almandine, also known as almandite, is a species of mineral belonging to the garnet group. The name is a corruption of alabandicus, which is the name applied by Pliny the Elder to a stone found or worked at Alabanda, a town in Caria in Asia Minor. Almandine is an iron alumina garnet, of deep red color, inclining to purple. It is frequently cut with a convex face, or en cabochon, and is then known as carbuncle. Viewed through the spectroscope in a strong light, it generally shows three characteristic absorption bands.

<span class="mw-page-title-main">Demantoid</span> Green gemstone variety of the mineral andradite

Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet group of minerals. Andradite is a calcium- and iron-rich garnet. The chemical formula is Ca3Fe2(SiO4)3 with chromium substitution as the cause of the demantoid green color. Ferric iron is the cause of the yellow in the stone.

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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 words for fire and eye. Despite being less common than most garnets, it is a widely used gemstone with numerous alternative names, some of which are misnomers. Chrome pyrope, and Bohemian garnet are two alternative names, the usage of the latter being discouraged by the Gemological Institute of America. Misnomers include Colorado ruby, Arizona ruby, California ruby, Rocky Mountain ruby, Elie Ruby, Bohemian carbuncle, and Cape ruby.

<span class="mw-page-title-main">Yttrium aluminium garnet</span> Synthetic crystalline material of the garnet group

Yttrium aluminium garnet (YAG, Y3Al5O12) 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 the monoclinic Y4Al2O9 (YAM).

Knorringite is a mineral species belonging to the garnet group, and forms a series with the species pyrope. It was discovered in 1968 in the Kao kimberlite pipe in the Butha-Buthe District of Lesotho and is named after Oleg Von Knorring, a professor of mineralogy at the University of Leeds in England.

<span class="mw-page-title-main">Spessartine</span> Nesosilicate, manganese aluminium garnet species

Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. This mineral is sometimes mistakenly referred to as spessartite.

<span class="mw-page-title-main">Grossular</span> Garnet, nesosilicate mineral

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 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. Grossular is a gemstone.

<span class="mw-page-title-main">Andradite</span> Nesosilicate mineral species of garnet

Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12.

<span class="mw-page-title-main">Hauyne</span> Silicate mineral

Hauyne or haüyne, also called hauynite or haüynite, is a tectosilicate sulfate mineral with endmember formula Na3Ca(Si3Al3)O12(SO4). As much as 5 wt % K2O may be present, and also H2O and Cl. It is a feldspathoid and a member of the sodalite group. Hauyne was first described in 1807 from samples discovered in Vesuvian lavas in Monte Somma, Italy, and was named in 1807 by Brunn-Neergard for the French crystallographer René Just Haüy (1743–1822). It is sometimes used as a gemstone.

<span class="mw-page-title-main">Rhodolite</span> Rose-colored gemstone of the garnet group

Rhodolite is a varietal name for rose-pink to red mineral pyrope, a species in the garnet group. It was first described from Cowee Valley, Macon County, North Carolina. The name is derived from the Greek "rhodon" for "rose-like", in common with other pink mineral types. This coloration, and the commonly inclusion-free nature of garnet from this locality, has led to rhodolite being used as a gemstone. Rhodolite like other varietal names is not officially recognized as a mineralogical term, but rather used as an accepted trade name.

<span class="mw-page-title-main">Hydrogrossular</span> Calcium aluminium garnet

Hydrogrossular is a calcium aluminium garnet series (formula: Ca3Al2(SiO4)3−x(OH)4x, with hydroxide (OH) partially replacing silica (SiO4)). The endmembers of the hydrogarnet family (grossular, hibschite, and katoite) depend on the degree of substitution (x):


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Further reading