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Garnet: description, properties and photo

Garnet

Garnets are a group of minerals with the same structure, but different chemical composition. Properties of the stone may also have differences due to its composition. For example, we can observe the various color of the mineral: red, orange, yellow, brown, green, yellowish green, pink, colorless, black and also with the color change effect. The name of the mineral comes from the latin “granatum” – the fruit of pomegranate, due to the similarity of the shape and the color of crystals with fruit grains. It is worth noting the physical properties of the stone: in addition to the variety of colors, its high hardness, excellent luster and strong dispersion.  

Garnet

Garnet varieties

Consider the properties and characteristics (descriptions) of garnets varieties. Two subgroups are distinguished in the mineral group depending on the chemical composition: pyralspites (mineral species: pyrope, almandine, spessartine); and ugrandites (mineral species: uvarovite, grossular and andradite). The composition may also be intermediate between its mineral species. The following are descriptions of the varieties of garnet with an indication of the characteristic color palette for each species.

PYROPE

Pyrope garnet colors: fiery red to dark red, sometimes brownish red. The name of the mineral comes from the greek “pyropos” is «fire». Pyropes are garnets, which are found in usually rounded grains, not crystals. In jewelry it is usually represented by small stones of a dark color. The cost of the pyrope mineral is about thirty dollars per carat. Go to pyrope encyclopedia.

ALMANDINE

Almandine is the most common species. Description of the color of almandine: red with a purple tint, less often deep red and dark brown. The name of the mineral is associated with Alabanda, a city in Asia Minor. Almandine is an inexpensive stone. Its cost is tens of dollars per carat. Good quality stones are more expensive than pyrope. Go to the Almandine Encyclopedia

RHODOLITE

Rhodolite is a commercial variety of garnet, intermediate in composition between pyrope and almandine. The name comes from the greek “rhodos” (rose) and “lithos” (stone). Color characteristic of rhodolite: from pink to pinkish red, violet red. The cost of rhodolite usually does not exceed $ 250 per carat, but occasionally there are very bright specimens with a cost of more than $ 1,000 per carat. Go to the Rhodolite encyclopedia

SPESSARTIN

Spessartine is less common than pyrope, almandine and rhodolite. Description of the color of spessartine garnet: orange, orangy red, brownish red, yellow. The name of this stone is given in honor of the Spessart Mountains in Germany, where it was first discovered. The cost of high quality spessartine can be more than $ 1,000 per carat. Go to Spessartine Encyclopedia

MALAYA GARNET

Malaya is a gemstone of pinkish-orange, reddish-orange or yellowish-orange color. It’s the most valuable variety of garnet. It has composition between pyrope and spessartine by chemical composition. Malaya garnet can sometimes have a color change effect. This is a very rare stone.

UVAROVITE

Uvarovit is a bright green stone. It presents in the form of small opaque crystals (usually up to 2-3 mm). This garnet will be named after the president of the Russian Academy of Sciences, collector of minerals S.S. Uvarov (1786-1855). The main uvarovite deposit is Saranovskoye in the Urals. There are also large size uvarovites in Finland- more than 1 cm across.

GROSSULAR

Grossular is a type of garnet mineral. Its classic color is green. From the latin language “grossularia” means “gooseberry”. The color in grossulars also can be green, yellowish-green, orange, yellow, pink, colorless. The price of green grossulars, for example, tsavorite and “mint garnet” can reach several thousand dollars per carat.

TSAVORITE

Tsavorite – garnet usually with saturated green color, a kind of grossular. Tsavorites got their name in honor of the place of the first find – Tsavo National Park in Kenya. The color of the tsavorite is similar to emerald, but in its rarity tsavorites exceed emeralds by about 300 times. Tsavorite is one of the most expensive garnets. Its cost can be measured in thousands of dollars per carat. Go to the tsavorite encyclopedia

MINT GARNET

Grossulars can be called mint garnet in trade because of their typical light green and light yellowish-green color. Sometimes such garnets are sold under the name «tsavorite». There is no clear distinction between these varieties on the market.

HESSONITE

Hessonite is a garnet variety of orange, yellow-brown, orange-red and brown-red. The name of the stone comes from the Greek word “hesson” – inferior. This is due to the fact that it was originally considered to be hyacinth (a kind of zircon), only with less hardness. Hessonite usually does not exceed $ 250 per carat.

ANDRADITE

Andradit is a garnet named after the Brazilian mineralogist J. B. d’Andrada, who first described the mineral in 1800. There are several varieties of andradite:

  1. Andradite, which has reddish brown color. It’s the most common type, rarely applied in jewelry.
  2. Topazolite is a yellow, yellowish brown gemstone. It is usually found in deposits along with another kind of andradite – demantoid.
  3. Demantoid is a very rare and most expensive variety of garnet. The name of the stone “demantoid” can be translated as “similar to a diamond.” The comparison with diamond is due to the fact that the play of color flashes in faceted demantoids is even more than in diamonds. Since the dispersion property of the demantoid (0.057) is higher than that of diamond (0.042). The color of the demantoid garnet is green, often with yellowish or brownish hues, rarely with a blue tint. For the first time, demantoids were found in the middle of the 19th century in Russia, in the Urals. The price of large high-quality Ural demantoids in the world market may exceed $ 10,000 per carat. The demantoid from the Urals is characterized by fine-fiber inclusions of byssolite called “horse tail”. Go to the demantoid encyclopedia.

The most valuable garnets are demantoid, tsavorite and spessartine. Garnets with color-changing properties are also very highly regarded. Their cost may exceed $ 1,000 per carat.

DEPOSITS

Pyropes were previously mined in Bohemia in the Czech Republic. Mines are also in South Africa and the United States. Gem quality almandines are found in India, Sri Lanka, Madagascar, Brazil, USA and Pakistan. Rhodolite is mainly mined in Sri Lanka, Tanzania and Madagascar. Spessartine deposits are known in Namibia, Nigeria and Mozambique. Spessartines are also produced in small quantities in Brazil, Myanmar, Madagascar, Tanzania, Sri Lanka, and the United States. Malaya garnet is mined in Kenya and Tanzania. Grossular deposits are known in Canada, Mexico, Brazil, Italy, Finland and Azerbaijan. Tsavorite is mined in Kenya, Tanzania and Madagascar. Hessonite is mined in Tanzania, in alluvial deposits of Sri Lanka and India, Madagascar, Mexico, Canada, small amount mined in US deposits. Uvarovite is mined in Russia in the Urals, in Finland, Kazakhstan and South Africa. Topazolites are mined in the Urals, in Italy, in the USA (New Jersey). In addition to the Urals, gem-grade demantoids enter the world market mainly from Namibia and Madagascar. Demantoids are also found in small amounts in Iran, Pakistan and Italy.

 

Garnet Mineral

Properties

Mineral:

pyrope, almandine, spessartine, uvarovite, grossular, andradite

Chemical formula:

A3B2 [SiO4] 3, where in pyralspites B = Al, A = Mg, Fe, Mn, and in ugrandites A = Ca, B = Fe, Cr, Al

Crystal Systems:

cubic

Mohs scale hardness:

6.5-7.5

Optical character:

Isotropic

Cleavage:

very imperfect

Density:

3.62-4.20 g / cm3

Luster:

Vitreous to adamantine

Refractive index: 

1.714 to 1.895

Birefringence: 

None

Dispersion: 

from 0.022 to 0.057

Color:

red, orange, green, with color changing effect and other colors

Interesting facts

  • Demantoid and tsavorite are the most expensive varieties of the garnet mineral. Their value can exceed $ 10,000 per 1 carat.
  • Color change garnets can be a great alternative to more expensive alexandrites.
  • Previously considered only characteristic for the Uralian demantoids, the inclusion of the bissolite as an "horsetail" was also found, for example, in demantoids from Pakistan, Iran and Italy.
Garnet Mineral

History

Garnets were known for 8 centuries BC. Almandine is mentioned in the writings of Pliny the Elder (1st century). Pyropes have been mined in Bohemia (Czech Republic) since the 13th century. Spessartines were first found in the mid-19th century in the Spessart Mountains, in Bavaria. Then they were mined in the USA. They began to enter the world trade arena with the discovery of large deposits in Namibia (1991) and Nigeria (1999). Campbell R. Bridges discovered the first tsavorites in 1967 in Tanzania near the village of Komolo. Later he discovered a tsavorite deposit on the Tanzanian border with Kenya in the Tsavo Park area. In 1974, the company Tiffany & Co. became interested in tsavorite, which later advertised this stone. Demantoids were first found in the middle of the 19th century in Russia, in the Urals. The find was then mistaken for peridot. And when in 1849 the Finnish mineralogist Nils Nordensköld arrived in Nizhny Tagil, he was shown the samples found. His research showed that the mineral is not peridot, but a type of garnet. In 1854, he spoke about the results of research at a meeting of the Imperial Mineralogical Society, and proposed the name “demantoid” for this gemstone in honor of his strong diamond-like “fire”.

Enhancement

Garnet gem varieties are usually not subjected to any kind of treatment. But demantoids can sometimes be subjected to low-temperature heat treatment in order to remove the brownish tint in some samples and “open” a greener color, or to slightly lighten the stone. The removing of a brownish tint in demantoids during heat treatment is associated with a change in the valence of iron. Heat treatment of demantoids is common for Ural stones, but there is no exact information on stones from Namibia and Madagascar. Demantoids of the Poldnevskoye deposit can be either heated or unheated. The demantoids of Bobrovka (Nizhny Tagil) are always without heat treatment, their color does not contain a brown hue. Demantoids of the Karkodinsky deposit are always heat-treated, for them this is a standard and necessary procedure. The fact that heat treatment of the demantoid in expert opinions is indicated by few gemological laboratories in the world. The fact that demantoids can heat in order to improve color, many international dealers began to know very recently.

Garnet

Photo

red garnet from Tanzania

On the photo: 11.71 carat red garnet from Tanzania

Set of green tsavorite garnets from Kenya

Set of green tsavorite garnets from Kenya

garnet demantoid from the Ural

On the photo: garnet demantoid from the Ural with horse tail type of bissolite inclusions

Orange hessonite garnets (Sri Lanka)

Orange hessonite garnets (Sri Lanka)

In the photo: Large red garnets and rhodolites from Sri Lanka

Two colors of a garnet weighing

Two colors of a garnet weighing 5.35 carats which has the effect of a color change (Tanzania)

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