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garnet1

  (gär'nĭt) pronunciation
n.
  1. Any of several common, widespread aluminum or calcium silicate minerals occurring in two internally isomorphic series, (Mg, Mn, Fe)3Al2Si3O12 and Ca3(Cr, Al, Fe)2Si3O12, generally crystallized, often embedded in igneous and metamorphic rocks, and colored red, brown, black, green, yellow, or white and used both as gemstones and as abrasives.
  2. A dark to very dark red.

[Middle English, from Old French grenate, from grenat, pomegranate-red, probably from Latin grānātum, pomegranate, from neuter of grānātus, seedy. See pomegranate.]


gar·net2 (gär'nĭt) pronunciation
n. Nautical.

A tackle for hoisting light cargo.

[Middle English garnett, probably from Middle Dutch garnāt.]


 
 

A hard, dense silicate mineral which occurs as crystals of cubic symmetry in a wide range of geologic environments. The general chemical formula of the silicate garnet group is A3B2(SiO4)3 where, in natural occurrences, the A cations are dominantly Fe2, Mn2, Mg, and Ca, and the B cations are Al, Fe3, and Cr3.

The garnet mineral group is generally divided into a number of individual species on the basis of chemical composition. The more common of these species are pyrope, almandine, spessartine, grossular, andradite, and uvarovite.

Garnets are substantially denser than most chemically analogous silicates, with specific gravities ranging between 3.58 (pyrope) and 4.32 (almandine). They also have high refractive indices (1.71–1.89) and hardness, on Mohs scale, of 6½ to 7½. The relative hardness, coupled with the absence of cleavage, has led to the use of garnet as an abrasive. The color of garnet is primarily controlled by its chemical composition. Uvarovite is emerald green; gem varieties of garnet are generally clear, deep red pyrope. See also Gem; Silicate minerals.

Garnets are widespread in their occurrence, particularly in rocks which formed at high temperatures and pressures. Because of the large, readily identifiable crystals which form, the first appearance of garnet is commonly used by geologists as an index of the intensity, or grade, of metamorphism. Garnets are strongly resistant to weathering and alteration and are hence widespread constituents of sands and sediments in areas of garnetiferous primary rocks. See also Metamorphic rocks.


 

Any of a group of common silicate minerals with identical crystal structure but highly variable chemical composition. Garnets are most often found in metamorphic rocks but also occur in certain types of igneous rocks, and, usually in minor amounts, in some sedimentary rocks. They may be colourless, black, or many shades of red and green. Garnets are hard, and they fracture with sharp edges. They are used as abrasives for fine sanding and polishing of wood, leather, glass, metals, and plastics, as sandblasting agents, and in nonskid surface coatings. Garnet is the birthstone for January. Garnets have been mined in New York, Maine, and Idaho in the U.S., the world's leading producer; notable quantities have also been found in Australia, China, India, and elsewhere.

For more information on garnet, visit Britannica.com.

 
Architecture: garnet

A mineral having many varieties in color and constituents but the same general chemical formula, with an isometric crystal structure.


 
name applied to a group of isomorphic minerals crystallizing in the cubic system. They are used chiefly as gems and as abrasives (as in garnet paper). The garnets are double silicates; one of the metallic elements is calcium, magnesium, ferrous iron, or manganese and the other aluminum, ferric iron, or chromium. Six varieties (of which there are also intermediate forms) are distinguished according to composition—grossularite (calcium-aluminum), pyrope (magnesium-aluminum), spessartite (manganese-aluminum), almandite (iron-aluminum), andradite (calcium-iron), and uvarovite (calcium-chromium). Grossularite occurs commonly in a red, green, yellow, or brown shade, depending on the impurities; if pure it would be colorless. The yellow and brown stones, coming chiefly from Sri Lanka, are used as gems under the names essonite (or hessonite) and cinnamon stone; sometimes they are miscalled hyacinth. Grossularite is found also in the Transvaal, in Mexico, and in Oregon. The most popular variety of garnet is the ruby-red pyrope from Bohemia, S Africa, and Arizona, sold as Cape ruby and Arizona ruby. Rhodolite, a mixture of pyrope and almandite from North Carolina, is rose-red or purple. Spessartite, a brown to brownish-red garnet from Bavaria, Sri Lanka, and parts of the United States, is seldom used for jewelry. Deep red, transparent almandite is the carbuncle; it was formerly a very popular gem. Almandites come chiefly from Brazil, India, and Sri Lanka; Australia and parts of the United States are also important sources. Andradite, a very common variety, is usually some shade of red, black, brown, yellow, or green. Gem varieties include topazolite, similar in color and transparency to topaz; demantoid, a green variety with a high dispersion and adamantine luster, sometimes miscalled olivine and Uralian emerald; and black melanite. Demantoid is found in the Urals, and the other andradites come chiefly from Europe and the United States. Uvarovite, an emerald-green variety from Russia and Finland, is rarely suitable for gem use. Garnet occurs in many different kinds of rocks—grossularite, in metamorphosed impure limestones; pyrope, in basic igneous rocks; spessartite, in granite rocks; almandite, in schists and other metamorphic rocks as well as in igneous rocks; andradite, in serpentine; and uvarovite, chiefly in serpentine.


 

Gemstone that was popularly believed to preserve health and promote joy, but in the case of lovers might cause discord.

 
Wikipedia: garnet


Garnet
GarnetCrystalUSGOV.jpg
General
Category nesosilicates
Chemical formula The general formula X3Y2(SiO4)3
Identification
Color virtually all colors
Crystal habit rhombic dodecahedra or cubic
Crystal system Isometric
Cleavage None
Fracture conchoidal to uneven
Mohs Scale hardness 6.0 - 7.5
Luster vitreous to resinous
Polish luster vitreous to subadamantine [1]
Refractive index 1.72 - 1.94
Optical Properties Single refractive, often anomalous double refractive [1]
Birefringence None
Pleochroism only in certain rare varieties
Streak White
Specific gravity 3.1 - 4.3
Major varieties
Pyrope Mg3Al2Si3O12
Almandine Fe3Al2Si3O12
Spessartite Mn3Al2Si3O12
Andradite Ca3Fe2Si3O12
Grossular Ca3Al2Si3O12
Uvarovite Ca3Cr2Si3O12

Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. Garnets are most often seen in red, but are available in a wide variety of colors spanning the entire spectrum. The name "garnet" comes from the Latin granatus ("grain"), possibly a reference to the Punica granatum ("pomegranate"), a plant with red seeds similar in shape, size, and color to some garnet crystals.

Six common species of garnet are recognized based on their chemical composition. They are pyrope, almandine, spessartite, grossular (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series; 1. pyrope-almandine-spessarite and 2. uvarovite-grossular-andradite.

Physical Properties

Appearance

Garnets species are found in many colors including red, orange, yellow, green, blue, purple, brown, black, pink and colorless. The rarest of these is the blue garnet, discovered in the late 1990s in Bekily, Madagascar. It is also found in parts of the United States, Russia and Turkey. It changes color from blue-green in the daylight to purple in incandescent light, as a result of the relatively high amounts of vanadium (about 1 wt.% 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. Because of their color changing quality, this kind of garnet is often mistaken for Alexandrite.

Garnet species’s light transmission properties can range from the gemstone-quality transparent specimens to the opaque varieties used for industrial purposes as abrasives. The mineral’s luster is categorized as vitreous (glass-like) or resinous (amber-like).

Crystal Structure

Molecular model of garnet.
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Molecular model of garnet.

Garnets are nesosilicates having the general formula X3Y2(SiO4)3. The X site is usually occupied by divalent cations (Ca2+, Mg2+, Fe2+) and the Y site by trivalent cations (Al3+, Fe3+, Cr3+) in an octahedral/tetrahedral framework with [SiO4]4− providing the tetrahedra[2]. Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit. (Note: the word "trapezohedron" as used here and in most mineral texts refers to the shape called a Deltoidal icositetrahedron in solid geometry.) They crystallize in the isometric system, having three axes that are all of equal length and perpendicular to each other. Garnets do not show cleavage, so when they fracture under stress, sharp irregular pieces are formed.

Hardness

Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this mineral group shows a range of hardness on the Mohs Scale of about 6.5 to 7.5. The harder species, like almandine, are often used for abrasive purposes.

Garnet group endmember species

Pyralspite garnets - Al in Y site

Almandine

Almandine in gneissic rock
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Almandine in gneissic rock

Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle (though originally almost any red gemstone was known by this name). The term "carbuncle" is derived from the Latin meaning "little spark." 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 Latin pyropos, means similar to fire. It is red in color and chemically a magnesium 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 almost black. Transparent pyropes are used as gemstones.

A variety of pyrope from Macon County, North Carolina is a violet-red shade and has been called rhodolite, from the Greek meaning "a rose." In chemical composition it may be considered as essentially an isomorphous mixture of pyrope and almandite, in the proportion of two parts pyrope to one part almandite. Pyrope has tradenames some of which are misnomers; Cape ruby, Arizona ruby, California ruby, Rocky Mountain ruby, and Bohemian garnet from the Czech Republic. Another intriguing find is the blue color-change garnets from Madagascar, a pyrope spessartine mix. The color of these blue garnets is not like sapphire blue in subdued daylight but more reminiscent of the grayish blues and greenish blues sometimes seen in spinel However in white LED light the color is equal to the best corn flower blue sapphire or D block tanzanite this is due to the blue garnets ability to absorb the yellow component of the emitted light.

Pyrope is an indicator mineral for high pressure rocks. The garnets from mantle derived rocks, peridotites and eclogites, commonly contain a pyrope variety.

Spessartine

Spessartine (the yellow mineral)
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Spessartine (the yellow mineral)

Spessartine or incorrectly spessartite is manganese aluminium garnet, Mn3Al2(SiO4)3. Its name is derived from Spessart in Bavaria. It occurs most often in granite pegmatite and allied rock types and in certain low grade metamorphic phyllites. Spessartine of a beautiful orange-yellow is found in Madagascar (see Mandarin garnet). Violet-red spessartines are found in rhyolites in Colorado and Maine.

Ugrandite group - calcium in X site

Andradite

Andradite (the black mineral)
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Andradite (the black mineral)

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 topazolite (yellow or green), demantoid (green) and melantite (black). Andradite is found both in deep-seated igneous rocks like syenite as well as serpentines, schists, and crystalline limestone. Demantoid has been called the "emerald of the Urals" from its occurrence there, and is one of the most prized of garnet varieties. Topazolite is a golden yellow variety and melanite is a black variety.

Grossular

Grossular on display at the US National Museum of Natural History.
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Grossular on display at the US National Museum of Natural History.

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 meaning inferior. Grossular is found in contact metamorphosed limestones with vesuvianite, diopside, wollastonite and wernerite.

One of the most sought after varieties of gem garnet is the fine green grossular garnet from Kenya and Tanzania called tsavorite. This garnet was discovered in the 1960s in the Tsavo area of Kenya, from which the gem takes its name.

Uvarovite

Uvarovite
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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.

Less common species

  • Calcium in X site
    • Goldmanite: Ca3V2(SiO4)3
    • Kimzeyite: Ca3(Zr,Ti)2[(Si,Al,Fe3+)O4]3
    • Morimotoite: Ca3Ti4+Fe2+(SiO4)3
    • Schorlomite: Ca3(Ti4+,Fe3+)2[(Si,Ti)O4]3
  • Hydroxide bearing - calcium in X site
    • Hydrogrossular: Ca3Al2(SiO4)3-x(OH)4x
      • Hibschite: Ca3Al2(SiO4)3-x(OH)4x (where x is between 0.2 and 1.5)
      • Katoite: Ca3Al2(SiO4)3-x(OH)4x (where x is greater than 1.5)
  • Magnesium or manganese in X site

Knorringite

Knorringite is a magnesium chromium garnet species with the formula Mg3Cr2(SiO4)3. Pure endmember knorringite never occurs in nature. Knorringite is only formed under high pressure and is often found in kimberlites. It is used as an indicator mineral in the search for diamonds.

Synthetic Garnets

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 behaviour. YIG is a ferrimagnetic material having a Curie temperature of 550 K. By substituting specific sites with rare earth elements, for example, interesting magnetic properties can be obtained.

One example for this is gadolinium gallium garnet, Gd3Ga2(GaO4)3, which is synthesized for use in magnetic bubble memory.

Yttrium aluminium garnet (YAG), Y3Al2(AlO4)3, is used for synthetic gemstone. When doped with neodymium (Nd3+), these YAl-garnets are useful as the lasing medium in lasers.

Geological importance of garnet

The Garnet group is a key mineral in interpreting the genesis of many igneous and metamorphic rocks via geothermobarometry. Diffusion of elements is relatively slow in garnet compared to rates in many other minerals, and garnets are also relatively resistant to alteration. Hence, individual garnets commonly preserve compositional zonations that are used to interpret the temperature-time histories of the rocks in which they grew. Garnet grains that lack compositional zonation commonly are interpreted as having been homogenized by diffusion, and the inferred homogenization also has implications for the temperature-time history of the host rock.

Garnets are also useful in defining metamorphic facies of rocks. For instance, eclogite can be defined as a rock of basalt composition, but mainly consisting of garnet and omphacite. Pyrope-rich garnet is restricted to relatively high-pressure metamorphic rocks, such as those in the lower crust and in the Earth's mantle. Peridotite may contain plagioclase, or aluminum-rich spinel, or pyrope-rich garnet, and the presence of each of the three minerals defines a pressure-temperature range in which the mineral could equilibrate with olivine plus pyroxene: the three are listed in order of increasing pressure for stability of the peridotite mineral assemblage. Hence, garnet peridotite must have been formed at great depth in the earth. Xenoliths of garnet peridotite have been carried up from depths of 100 km and greater by kimberlite, and garnets from such disaggegated xenoliths are used as a kimberlite indicator minerals in diamond prospecting. At depths of about 300 to 400 km and greater, a pyroxene component is dissolved in garnet, by the substitution of (Mg,Fe) plus Si for 2Al in the octahedral (Y) site in the garnet structure, creating unusually silica-rich garnets that have solid solution towards Majorite. Such silica-rich garnets have been identified as inclusions within diamonds.

Uses of garnets

Pendant in uvarovite, a rare bright-green garnet.
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Pendant in uvarovite, a rare bright-green garnet.

Pure crystals of garnet are used as gemstones. Garnet sand is a good abrasive, and a common replacement for silica sand in sand blasting. Mixed with very high pressure water, garnet is used to cut steel and other materials in water jets. Garnet sand is also used for water filtration media.


References

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Wikimedia Commons has media related to:
  1. ^ a b c
  2. ^ Smyth, Joe. Mineral Structure Data. Garnet. University of Colorado. Retrieved on 2007-01-12.
  3. ^ LongLocks HairSticks® Boutique's Birthstones and Anniversary Gemstones Chart; LongLocks HairSticks® Boutique; retrieved on October 4, 2007
  4. ^ State of Connecticut, Sites º Seals º Symbols; Connecticut State Register & Manual; retrieved on January 4, 2007
  5. ^ New York State Gem; State Symbols USA; retrieved on October 12, 2007

 
Translations: Translations for: Garnet

Dansk (Danish)
1.
n. - hejsetakkel, givtov til undersejl

2.
n. - granat

Nederlands (Dutch)
granaat(steen/ -rood)

Français (French)
1.
n. - (Minér) grenat

2.
n. - appareil de levage

Deutsch (German)
1.
n. - (min.) Granat, Granatfarbe

2.
n. - (naut) Garnat, Ausrüstung für das Hochziehen leichter Ladung

Ελληνική (Greek)
n. - (ορυκτολ.) γρανάτης

Italiano (Italian)
granato

Português (Portuguese)
n. - granada (f) (Miner.), cor (f) vermelho-escura

Русский (Russian)
гранат (минерал), гранатовый, темно-красный цвет

Español (Spanish)
1.
n. - granate

2.
n. - variedad rojo oscuro de minerales duros y vítreos

Svenska (Swedish)
n. - granat (miner.), granatrött

中文(简体) (Chinese (Simplified))
石榴石, 深红色

中文(繁體) (Chinese (Traditional))
n. - 石榴石, 深紅色

한국어 (Korean)
1.
n. - 석류석

2.
n. - 진홍색

日本語 (Japanese)
n. - ざくろ石, ガーネット色, ガーネット

العربيه (Arabic)
‏(الاسم) عقيق أحمر‏

עברית (Hebrew)
n. - ‮נופך, אדום עז, אבן יקרה‬
n. - ‮מנוף למטענים קלים‬


 
 

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
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Occultism & Parapsychology Encyclopedia. Encyclopedia of Occultism and Parapsychology. Copyright © 2001 by The Gale Group, Inc. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Garnet" Read more
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