INTRO NAEEM ULLAH

TOPIC GARNET FAMILY

ETYMOLOGY The garnet (pronounced /ˈɡɑrnɨt/) group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" comes from 14th century Middle English word gernet meaning 'dark red', from the Latin granatus granatus coming from granum (grain, seed) + suffix "atus", possibly a reference to "mela granatum" or even "pomum granatum" ("pomegranate", scientific name: "Punica granatum"), a plant whose abundant vivid red arils contained in the fruit are similar in shape, size, and color to some garnet crystals.

Introduction Garnet is a common mineral of metamorphic rocks such as gneiss and schist of all description from basic to acid, crystalline limestone and pegmatite.

History The History Says It is said that Noah used a garnet on the bow of his ark to help navigate at night, and garnets have long been carried by people who are traveling, because they believe it will protect them from accidents. Legend has it that garnets protect their owners from nightmares, and garnets were even used as bullets because the shooters thought the red color would increase the intensity of the wound.

Six basic species of Garnet Group Almandine 2. Pyrope 3. Spessartine 4. Grossularite 5. Uvarovite 6. Andradite

1. Solid solution series 1. Almandine 2. Pyrope 3. Spessartine

2. Second solution seires 4. Grossularite 5. Uvarovite 6. Andradite

Isometric (rhombic, dodecahedron, isoctohedron, and trapezohedron) Name: Garnet Family Chem: Mg3Al2(SiO4)3 - Fe3Al2(SiO4)3 -Mn3Al2(SiO4)3 Pyrope - Almandine - Spessartite Crystal: Isometric (rhombic, dodecahedron, isoctohedron, and trapezohedron) Color: red, red-brown, black, green, orange, purple, yellow Refrac. Index: 1.69 - 1.86 Birefraction: 0.022 - 0.057 Hardness: 6.5 - 7.5 Spec. Grav.: 3.6 - 4.2 Fracture: conchoidal Cleavage: imperfect Environment: garnets area solid solution series, and occur in contact metamorphics, serpentines Association: scapolite, diopside, calcite, wollastonite, kimberlite, tremolite Locals: | Italy | Turkey | Calif.., N.J., N.C., Col., USA | Sri Lanka | Norway | Bohemia | Misc: The name almandine comes from the Anotolian city of Alabanda; the name Andradite comes from the Brazilian mineralogist J.B. d'Andrada; the name Grossular comes from the Greek "grossularia", "meaning gooseberry"; the name Pyrope comes from the Greek "pyropos", meaning "fire-eyed" for its red color; the name Spessartite comes from Spessart mining district in Bavaria; and the name Uvarovite comes from the Russian noble man, Count Sergei Uvarov. The garnets make up two solid solution series; 1) pyrope-almandine-spessarite and 2) uvarovite-grossularite-andradite. The majority of garnet goes into the manufacture of sand-paper.

Formation Garnet can occur in both metaluminous and peraluminous granitoid rocks, but usually only as an accessory phase. Its stability is a complex function of temperature and pressure.

The garnet family is as chemically complex as its variety suggests The garnet family is as chemically complex as its variety suggests. In fact garnet is a group of six closely related minerals: almandine, pyrope, grossular, spessartite, andradite, and uvarovite. In practice many garnets contain a mixture of two or more of these varieties. The trade has names for some of the more distinctive blends, which include purplish red to pink rhodolite and sunset orange Malaya, some of the most popular garnets today.

Garnet group The Garnet Group is actually a larger group than most people realize. In the table below are the more common members with their chemistries and their significant divergent properties: density (SG), index of refraction (IR), and the typical color as well as their general environment of formation. Under environment of formation: metamorphic is indicated with an M and igneous with an I. All garnets may contribute to detrital sedimentary rocks but they are not of original sedimentary origin.

Ca3Al2(SiO4)3 Mg3Al2(SiO4)3 Mn3Al2(SiO4)3 Ca3Cr2(SiO4)3 Mineral Name: Chemistry: SpecificGravity: Index ofRefraction: Typical Color: Environment of Formation: ALMANDINE Fe3Al2(SiO4)3 SG = 4.3 IR = 1.83 reddish brown to brown M-schists & gneisses;I-pegmatites (rarely) ANDRADITE Ca3Fe2(SiO4)3 SG = 3.8 IR = 1.89 brown, black or green M-serpentinites& skarns; I-volcanic GROSSULAR Ca3Al2(SiO4)3 SG = 3.5 IR = 1.75 colorless, orange or green M-contact marbles &serpentinites PYROPE Mg3Al2(SiO4)3 SG = 3.6 IR = 1.73 dark red to ruby red M-serpentinites& gneisses; I-dunites&kimberlites SPESSARTINE Mn3Al2(SiO4)3 SG = 4.2 IR = 1.80 orange, pink or brown M-gneisses marbles I-pegmatites & granites UVAROVITE Ca3Cr2(SiO4)3 IR = 1.86 green M-serpentinites

Almandine 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 "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 mic schist, 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 "fire-eyed") is red in color and chemically a magnesium aluminum 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 almandine, in the proportion of two parts pyrope to one part almandine. Pyrope has trade names 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-changing 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 cornflower blue sapphire, or D block tanzanite; this is due to the blue garnet's 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 or spessartite is manganese aluminum 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 an orange-yellow is found in Madagascar. Violet-red spessartines are found in rhyolites in Colorado and Maine.

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 aluminum 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. 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 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.

Andradite Andradite is a calcium-iron garnet, Ca3Fe2(SiO4)3, is of variable composition and may be red, yellow, brown, green or black. The recognized varieties are topazolite (yellow or green), demantoid (green) and melanite (black). Andradite is found both in deep-seated igneous rocks like syenite as well as serpentines, schist, 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.

Doesn't refer to a single name Garnet Doesn't refer to a single name Some basic varieties

A variety of Grossularite Tsavorite A variety of Grossularite

Spessartine Rhodotite

Malaya Hydrogrossular

Tsavorite: Tsavorite is a green garnet that can have very deep bright colors, the best of which rival emerald. Tsavorite is one of the more expensive garnets.

Spessartine Spessartine is the manganese-aluminum member of the garnet family. Chemical Formula ----Mn3Al2(SiO4)3. The color ranges from yellowish to reddish orange.  

Rhodotite Rhodolite is a mixture of almandine and pyrope,{the magnesium- aluminum garnet, Mg3Al2(SiO4)3}. Its Chemical Formula could be written ---- Fe/Mg3Al2(SiO4)3. If either Fe or Mg exceeds 60% of the composition, the stone is judged to be Almandine or Pyrope. The color ranges from brownish red to purplish red.

Malaya Malaia garnet or Malaya garnet is a gemological varietal name for light to dark pinkish orange, reddish orange, or yellowish orange garnet, that are a mixture of pyrope and spessartite. It is found in east Africa, in the Umba Valley bordering Tanzania and Kenya. Malaia was at first believed to be a type of spessartite garnet. During the 1970's rough malaia garnets were being mixed with parcels of Rhodolite garnet being offered for sale. These odd color stones were rejected, and the name given to this type of garnet was Malaia, which is a Swahili word meaning outcast. It came into usage for a number of garnets that did not fit into any of the standard categories.  Color change garnets are mostly pyrope and spessartite in composition. Except for the color change, they are identical in properties to the Malaia variety. Their primary source is Africa.

Hydrogrossular Hydrogrossular, is a calcium aluminum garnet series (formula: Ca3Al2(SiO4)3-x(OH)4x, with hydroxide (OH) partially replacing silica (SiO4)). The end members of the hydrogarnet family (grossular, hibschite, and katoite) depend on the degree of substitution (x): grossular: x = 0 hibschite: 0.2 < x < 1.5 katoite: 1.5 < x < 3. Hydrogrossular is a garnet variety in which a Si4+ is missing from a tetrahedral site. Charge balance is maintained by bonding a H+ to each of the four oxygens surrounding the vacant site. Hydrogrossular is found in massive crystal habit, sometimes grown in with idocrase. Hydrogrossular is translucent to opaque, and found in green to bluish green, pink, white, and gray. The cause of the green color is chromium, and possibly iron. Pink hydrogrossular is caused by the presence of manganese. Hydrogrossular may have dark gray to black small inclusions It has similarities to jade, and has the misnomers Transvaal jade, and African jade. Hydrogrossular is sometimes used as a gemstone, being cabochon cut, or made intobeads. Sources for green and pink hydrogrossular are South Africa, Canada, and the United States. White hydrogrossular is sourced from Burma and China.

Localities in the world Garnet is found in Africa, Brazil, Canada, India, Madagascar, Sri Lanka, and the USA (Arizona, Colorado, Georgia, Idaho, New Hampshire, New Mexico, North Carolina, Pennsylvania, Utah, and Virginia).

Bajaur Agency, Appu Aligund, Fuljo, Braldu, Bashu, Karma Localities in the Pakistan Bajaur Agency, Appu Aligund, Fuljo, Braldu, Bashu, Karma

A variety of Grossularite Almandine Desired color, Green Tsavorite A variety of Grossularite

Tsavorite Tsavorite or tsavolite is a variety of the garnet group species grossular, a calcium-aluminum garnet with the formula Ca3Al2Si3O12. Trace amounts of vanadium or chromium provide the green color.

Origin Grossularite is a calcium-aluminium garnet with the formula Ca3Al2(SiO4)3, though the calcium may in part be replaced by ferrous iron and the aluminum by ferric iron. The name grossularite 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. Grossularite is found in 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.[

Synthetic Garnets The crystallographic structure of garnets has been expanded from the prototype to include chemicals with the general formula A3B2(C O4)3. Besides silicon, a large number of elements have been put on the C site, including Ge, Ga, Al, V and Fe. Yttrium aluminum 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+), these YAl-garnets may be used as the lasing medium in lasers.

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

Treatment of Garnet Garnet stones come in a variety of colors from red and orange to green and pink and purple, gold and brown. Like many gemstones, garnets may be heat-treated to enhance their natural color. This treatment does not alter the stone's need for gentle treatment during cleaning. Although garnets are tough stones, chemicals may corrode them and sudden temperature changes can cause fractures. Overall, garnet is very easy to clean.

Care You can clean your garnet with warm soapy water and a soft brush. Always make sure you rinse the stone well after washing it. Ultrasonic treatments may also be used for any garnets except the demantoid variety. Do not steam clean your garnet. As with other stones, one should take care of their garnet and protect it from sharp blows, harsh temperatures and chemicals.

Price Spessartite Spessartite garnet ranges in color from a vivid orange to reddish orange and orange-red. The orange color derives from manganese, while the addition of traces of iron produce a redder color. The finest specimens come from Nigeria, including some which are a very pure mandarin orange. Prices range from around $300 a carat for high quality orange-red stones to over $2,000 a carat for the top vivid orange in large sizes. 

Tsavorite Tsavorite garnet is a rare grossularite garnet colored by chromium. Discovered only in the 1960's, almost all the tsavorite in the world comes from a small area at the intersection of Tanzania and Kenya in east Africa. The best tsavorites rival emerald in color. Found mainly in small sizes, tsavorites over 2 carats are very rare. Prices range from $500 a carat for good colors with some inclusions, to $1,000 to $2,000 for clean larger stones with top color.

Demantoid Demantoid garnet is the rarest and most valuable of the garnets and is one of the rarest of all colored gemstones. It is remarkable for its brilliance and fire. The most valuable demantoid comes from Russia, and is distinguished by unique horsetail-pattern inclusions of byssolite. The vivid green color is the most valuable and stones over 1 carat are very rare. Prices for Russian demantoid start at about $1,000 per carat. There is also some demantoid from Africa without horsetail inclusions that is less expensive.

Rhodolite garnet Rhodolite garnet is a mixture of almandine and pyrope garnet that is valued for its purplish-red or raspberry color. Unlike the common dark red garnets, rhodolite tends to be lighter in tone and lacks the brownish secondary hue. Rhodolite is the least expensive of the rarer garnets and high quality specimens can be found for as little as $40-$50 per carat.

Color-change garnet Color-change garnet is usually a mixture of pyrope and spessartite garnets that displays different colors under daylight and incandescent light. This phenomenon is rare and valued by collectors. There is a range of color change, but green or bluish green to red or purple tends to be the most dramatic. These rare garnets have been found in Kenya and Madagascar and prices range from about $500 to $1,000 per carat, depending on size, color and clarity.

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