Garnet
Garnet is the group of differently coloured minerals which have similar crystal structure and same chemical composition. The name garnet derives from the Latin for grain means round crystal. Similarity to the red kernals of the pomegranate. It could have come from another medieval Latin Word "granum" that refer to red dye. Garnet in a gem group that has over twenty varieties among these varieties only six of them are used as gems. These are pyrope, Almandite, Spessartite, Grossularite, Andradite and Uvarovite.
Pyrope Garnet:
The name of pyrope garnet derives from the Greek word mean fiery. It's color is deep red and cause of color is chromium. It was a fashion stone of the 18th and 19th centuries.
Almandite:
Its name is derived from the town in Asia Minor. Its color is red with violet tint and cause of color is chromium and iron.
The composition of pyrope and almandite garnet is called Rhodolite. It is purplish red or rose color garnet.
Spessartite:
Its name derived from occurrence in the 'spessart' [Germany: means forest]. It is also known as mandarin garnet for its vivid orange color. It is one of the rarest members of the garnet family. Its color is orange, yellow-orange, brown orange and red orange. The cause of color is manganese and iron.
Grossularite (Grossular):
Its name is derived from the Greek word grossularia for gooseberry. In its pure state grossular garnet is colorless. It often takes on color from impurities it contains that's why the stone can be found in a wide range of colors. Grossular garnet is differentiate with four different varities such as Hessonite, Leuco garnet, Rosolite and Tsavorite.
- Hessonite : It is orange and brown to red verity. It is also called cinnamon stone and kaneel stone. Cause of color is iron and manganese.
- Leuco Garnet : It is the colorless variety. There are no impurities in it.
- Rosolite : It is pink in color. The cause of color is iron.
- Tsavorite : It is green in color. There are two varieties of green grossular one is tsavorite and other is Transvaal jade. The transparent crystal form is tsavorite and the massive green groussular form is Transvaal. Transvaal may contain black specks of the mineral magnetite. The cause of color is vanadium and sometimes chromium.
Andradite:
Andradite the stone is named for the Brazilian mineralogist J. B de Andrada e Silva. It is green or emerald green in color. The cause of color is manganese, titanium, aluminium or chromium. The wide range of colors differential its variety. It is generally three types of andradite are found such as Demantoid, Melanite and Topazolite.
- Demantoid : It is green and emerald green in color. It is the most valuable variety in the garnet species. Cause of color is chromium. The name demantoid came after means diamond like luster. It can be recognized by the typical inclusion "horsetails".
- Melanite : It is opaque black variety. It can be found in deep blackish red in color. The cause of color is titanium.
- Topazolite : It is yellow to lemon yellow in color. It looks like a topaz and that's why it is called topazolite. The cause of color is iron.
Uvarovite:
Its name is derived for count uvarov a Russian staleman who made it his life's work to catalogue the mineral weath of his country. It is rarely used as a gem because its crystals are too small to be cut. It is green in color. The cause of color is chromium.
Deposits
Garnets come mainly from African countries, but are also found in India, Russia and Central and South America.
- Pyrope : Czechoslovakia, Burma, China Madagascar, Srilanka, South Africa and The United States.
- Almandite : Brazil,India,Madagascar,Srilanka,Norway,Pakistan,Russia,United States,Czech Republic and Austria.
- Grossularite (Hessouite) : Srilanka,Brazil,India,Canada,Madagascar,Tanzania Siberia and The United States.
- Leuco garnet : Canada,Mexico and Tanzania.
- Tsavorite : South Africa,Burma,Zambia,Kenya, Tanzania.
- Andradite (Demantoid) : China,Korea,Russia and The United States.
- Melanite : Germany,France,Italy,Colorado.
- Topazolite : Switzerland,Italy and California.
- Uvarovile : India, Finland,Canada,Poland,Russia,California.
- Spessarite : Germany, Burma, Brazil, China, Kenya, Madagascar, Srilanka, Tanzania, Namibia, Nigeria.
Properties of Garnet
| Species | GADOLINIUM GALLIUM GARNET (GGG) |
|---|---|
| Variety | GGG |
| Chem. System | Gd3 Ga5 O12 Gadolinium Gallium Oxide. |
| Cryst. System | Cubic |
| Habit | Long boules |
| Colour | Orange, Yellow, Blue, White |
| Cause of Colour | Rare earth elements |
| Transparency | Transparent |
| Luster | Admantine |
| Hardness | 6.5 |
| S . G | 7.05 |
| Cleavage | None |
| Fracture | Conchoidal |
| SR/DR | SR |
| Pleochroism | None |
| Optic Sign | None |
| Optic Char | None |
| R.I. Range | 1.92 to 2.05 |
| Birefringence | None |
| Spectrum | Varies with colour, Generally rare earth spectrum is seen. |
| Dispersion | 0.045 |
| Inclusion | Gas bubbles |
| U . V. Light | Pinkish orange in SW |
| Simulants | Diamond, CZ, YAG, ST, Synthetic Rutile |
| Treatment | None |
| Manufacturing | Czochralski, Kyropolous |
| methods | |
| Trade Name | GGG |
| Indian Name | Synthetic Garnet, GGG. |
| Species | GAHNITE |
|---|---|
| Variety | Gahnite (zinc - Spinel) |
| Chem. System | Zn Al2 O4 (Zinc aluminate) |
| Cryst. System | Cubic |
| Habit | Octahedral |
| Colour | Green, Blue, Violet. |
| Cause of Colour | Iron |
| Transparency | Transparent |
| Luster | Vitreous to greasy |
| Hardness | |
| S . G | 4.4 |
| Cleavage | |
| Fracture | |
| SR/DR | SR |
| Pleochroism | None |
| Optic Sign | None |
| Optic Char | None |
| R.I. Range | 1.805 |
| Birefringence | None |
| Spectrum | None characteristic |
| Dispersion | 0.019 - 0.021 (C-F) |
| Inclusion | Appears black in reflected light |
| U . V. Light | Inert |
| Simulants | Spinel, synthetic gahnite |
| Treatment | None |
| Location | Bowaria, Kopparberg, New Jersey, Sweden |
| Trade Name | Gahnite, zinc spinel |
| Indian Name | Gahnite. |
| Species | GARNET |
|---|---|
| Variety | Almandine |
| Chem. System | 3 Feo, Al2 O3 3SiO2 (Iron aluminium silicate). |
| Cryst. System | Cubic |
| Habit | Dedecahedral |
| Colour | Red to brownish - red to Violet red, darker red. |
| Cause of Colour | Iron |
| Transparency | Transparent to opaque |
| Luster | Vitreous |
| Hardness | 7.5 |
| S . G | 3.90 - 4.20 |
| Cleavage | Distinct parting |
| Fracture | Conchoidal |
| SR/DR | SR generally clear DR effect, ADR |
| Pleochroism | None |
| Optic Sign | None |
| Optic Char | None |
| R.I. Range | 1.76 to 1.81 |
| Birefringence | None |
| Spectrum | Main three bands : 3950, 4040, 4380, 4620, 4760 A0 ; Other bands : 5050, 5270, 5760 A0 |
| Dispersion | 0.027 |
| Inclusion | Silk', rutile needles cross one another at 700 & 1100. Crystal, hornblende rods and Zircon halos. |
| U . V. Light | Inert |
| Simulants | Paste, tourmalin, spinel, ruby, other reddish garnets. |
| Treatment | Used in garnet topped doublets, heat, dyeing. |
| Location | India, Sri-Lanka, Tanzania, Zambia, Madagascar, America, Brazil. |
| Trade Name | Almandine Garnet |
| Indian Name | Tambda, Garnet |
| Species | GARNET |
|---|---|
| Variety | Andradite, demantoid, topazolite, melanite |
| Chem. System | Ca3 Fe2 (SiO4)3 (Calcium iron silicate). |
| Cryst. System | Cubic |
| Habit | Dedecahedral |
| Colour | Yellow and green often with eye visible dispersion. yellow-topazolite, green - demantoid, opaque ; black - melanite. |
| Cause of Colour | Green - Chromium, iron. Yellow - iron. Black - iron and titanium. |
| Transparency | Transparent to opaque |
| Luster | Sub - adamantine |
| Hardness | 6.5 |
| S . G | 3.82 - 3.85 |
| Cleavage | None |
| Fracture | Conchoidal |
| SR/DR | SR (ADR) |
| Pleochroism | None |
| Optic Sign | None |
| Optic Char | None |
| R.I. Range | 1.89 |
| Birefringence | None |
| Spectrum | 4430 A0 plus chromium spectrum at 6200, 6400, 6930, 7010, A0. |
| Dispersion | 0.057 |
| Inclusion | Horse- tail like inclusion made of byssolite (asbestos) fibres - characteristic of demantoid. |
| U . V. Light | Inert |
| Simulants | Green coloured sphene, apatite, peridot, tourmaline, zircon, sapphire, quartz |
| Treatment | None |
| Location | Ural mountainns, Zaire, Italy, Switzerland, Arizona |
| Trade Name | Andradite garnet, demantoid garnet, melanite garnet, topazolite garnet. |
| Indian Name | Garnet |
| Species | GARNET |
|---|---|
| Variety | Massive grossular, hessonite, tsavorite |
| Chem. System | Ca3 Al2 (SiO4)3 (Calcium aluminium silicate). |
| Cryst. System | Cubic |
| Habit | Dedecahedral |
| Colour | Hessonite : medium to dark orange, brown orange to brownish yellow. |
| Tsavorite : medium light to dark green to yellowish green. | |
| Massive grossular : transluscent green. | |
| Cause of Colour | Tsavorite : Chromium & vanadium, Massive grossular : Green- chromium, Pink- managanese. |
| Transparency | Transparent to opaque |
| Luster | Greasy |
| Hardness | 7.25 |
| S . G | Massive grossular : 3.36 to 3.55, Hessonite : 3.65, Tsavorite : 3.57 to 3.65 |
| Cleavage | Parting |
| Fracture | Conchoidal |
| SR/DR | SR |
| Pleochroism | None |
| Optic Sign | None |
| Optic Char | None |
| R.I. Range | Massive grossular : 1.70 to 1.73, Hessonite : 1.742 to 1.748, Tsavorite : 1.739 to 1.744 |
| Birefringence | None |
| Spectrum | Varies with colour. Hessonite - no charactristic spectrum, but may show almandine spectrum due to almandine molecules. |
| Dispersion | 0.027 |
| Inclusion | Horse- tail like inclusion made of byssolite (asbestos) fibres - characteristic of demantoid. |
| U . V. Light | Dyeing, irradiation, heat |
| Simulants | Oily streak called treacle, eroded crystals, a fused appearance, and heat wave effect are typical of hessonite. yellow fibers, veil like inclusion seen in tsavorite. |
| Treatment | None |
| Location | India, Sri-Lanka, S.Africa, Swat in Pakistan, USA, Brazil, Tanzania, Kenya |
| Trade Name | Cinnamon stone or hessonite garnet, tsavorite, transvaal jade. |
| Indian Name | Gomedah, Garnet |
| Species | GARNET |
|---|---|
| Variety | Pyrope |
| Chem. System | Mg3 Al2 (SiO4)3 (magnesium aluminium silicate). |
| Cryst. System | Cubic |
| Habit | Dedecahedral |
| Colour | Deep bloodred |
| Cause of Colour | Chromium |
| Transparency | Transparent to opaque |
| Luster | Vitreous |
| Hardness | 7.25 |
| S . G | 3.70 to 3.90 |
| Cleavage | Distinct Parting |
| Fracture | Conchoidal |
| SR/DR | SR |
| Pleochroism | None |
| Optic Sign | None |
| Optic Char | None |
| R.I. Range | 1.73 to 1.76 |
| Birefringence | None |
| Spectrum | Main three band : 5050, 5270, 5750 A0. Other Bands : 5700, 6500, 6710, 6850, 6870 A0. |
| Dispersion | 0.022 |
| Inclusion | Zircon haloes, rutile needle, rounded irregular crystal, quartz crystal. |
| U . V. Light | Inert |
| Simulants | Spinel, ruby & other reddish garnets, paste, tourmaline. |
| Treatment | Heat |
| Location | India, SriLanka, Tanzania, Zambia, Madagascar, America. |
| Trade Name | Pyrope garnet |
| Indian Name | Tambda, Garnet |
| Species | GARNET |
|---|---|
| Variety | Spessartite |
| Chem. System | Mn3 Al2 (SiO4)3 (magnesium aluminium silicate). |
| Cryst. System | Cubic |
| Habit | Dedecahedral |
| Colour | Yelloworange, brown orange to redorange |
| Cause of Colour | Manganese & iron. |
| Transparency | Transparent to opaque |
| Luster | Vitreous |
| Hardness | 7.25 |
| S . G | 4.12 to 4.20 |
| Cleavage | Parting |
| Fracture | Conchoidal |
| SR/DR | SR |
| Pleochroism | None |
| Optic Sign | None |
| Optic Char | None |
| R.I. Range | 1.79 to 1.81 |
| Birefringence | None |
| Spectrum | 4120, 4240, 4320, 4620, 4850, 4950, 5050 Ao |
| Dispersion | 0.027 |
| Inclusion | Wavy feathers formed by liquid drops with peculiar shreded appearance |
| U . V. Light | Inert |
| Simulants | Other garnets, zircon, apatite, tourmaline, paste. |
| Treatment | None |
| Location | SriLanka, Burma, Madagascar, Norway, Italy, Bavaria, Brazil, USA, India. |
| Trade Name | Spessartite garnet |
| Indian Name | Spessartite garnet |
| Species | GARNET |
|---|---|
| Variety | Uvarovite |
| Chem. System | Ca3 Cr2 (SiO4)3 (Chromium Calcium silicate). |
| Cryst. System | Cubic |
| Habit | Dedecahedral |
| Colour | Chrome coloured green garnet resembling emerald in appearance |
| Cause of Colour | Chromium |
| Transparency | Transparent to opaque |
| Luster | Vitreous |
| Hardness | 7.5 |
| S . G | 3.77 |
| Cleavage | Parting |
| Fracture | Conchoidal |
| SR/DR | SR |
| Pleochroism | None |
| Optic Sign | None |
| Optic Char | None |
| R.I. Range | 1.87 |
| Birefringence | None |
| Spectrum | Chromium spectrum |
| Dispersion | 0.014 0.021 |
| Inclusion | Black Crystal |
| U . V. Light | Red under LW |
| Simulants | Emarald, tourmaline, jadeite, idocrase, apatite, zircon |
| Treatment | None |
| Location | Ural mountains, India Himalayas, California, Canada, Poland |
| Trade Name | Green garnet |
| Indian Name | Green garnet |
Inclusion
Crystal, hornblende rods and zircon halos, Rutile needle, quartz crystal , rounded irregular crystals.
Simulants
Paste, tourmalin, spinel, ruby, other reddish garnets.
Famous Garnet
Many gemstone buyers associate garnet with the deep red stones that were enormously popular in European jewelry in the 19th and 18th centuries. These inexpensive garnets mainly belong to the almandine and pyrope varieties. Though they have good hardness and brilliance, they tend to have a distinct brownish tone that makes them less attractive than more expensive red gems such as ruby or rubellite tourmaline.
However, there are some rare garnet varieties that are much sought after by gem dealers and collectors. These varieties include the mandarin orange spessartite garnet; the green tsavorite and demantoid garnets; the purplish red rhodolite garnet; the unique color-change garnet; and the very rare colorless leuco garnet. If you think garnet is rather common, these unusual garnets will change your mind.
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| 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. For more information see our article on Spessartite Garnet Prices. |
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| Tsavorite garnet is a rare grossular 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. |
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| 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. |
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| Malaia Garnet is a pyrope-almandine-spessartite mixture that is also know as Malaya Garnet or Imperial Garnet. It is found in a range of hues, from slightly pinkish orange to reddish orange or yellowish orange. Tone can vary from light to dark. Malaia garnet was first discovered in the early 1970's in the Umba River valley that borders northern Tanzania and southern Kenya. Deposits of similar material were also found in 1993 in southern Tanzania. Fine quality stones in larger sizes sell for $300-$400 per carat. |
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| 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. Some unusual vivid purple garnets were recently discovered in Mozambique. |
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| 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 $1,500 per carat, depending on size, color and quality. |
