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Encyclopedia

A B C D E F
G H I J K L M N O P Q R S T U V W X Y Z

Gahnite: Zn Al2 O4Gahnite ©Gemfrance.com
Etymology : mineral species discovered by the Swedish chemist / mineralogist J.G. GAHN (1745-1818).
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Garnet:
Grenat (French), Granat (German), Granate(Spansih), Granato (Italian), Granat(Turkish), гранат (Russian), γρανάτης (Greek), 石榴石 (Chinese), ガーネット(Japanese), สี แดง เข้ม (Thai),נוֹפֶך (Hebraic), العقيق(Arabic).
Etymology : from the Latin "granatus" = like seeds, probably referring its resemblance to pomegranate seeds.
In the Middle Ages, garnet was called "escarboucle", from the latin "carbunculus"= small ember.
When one says « garnet colored », generally one thinks of red. However, garnet exists in all colors. One of the most sought after garnets is the green garnet called "demantoid".
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Garnet - andradite: Ca3 Fe2 +3 (SiO4)3
Discovered by par Dana in 1868.
Color : green yellow, yellowish green, brown, greenish brown, reddish, grayish black, colorless, brownish red, green
Etymology : in memory of the Brasilian mineralogist J.B. d’ANDRADA E SILVA (1763-1838).

Garnet - Demantoid:デマントイド a variety of green garnet (andradite).
Etymology : from "adamas", diamond in Greek, because its high dispersion resembles that of a diamond.
It’s one of the rarest green garnets. The mine that is the best known is that in the Ural Mountains in Russia. The existence of demantoid garnet in this area has been known since the reign of Tsar Alexander II. Other discoveries of demantoid garnet have since been made in Namibia and more recently, in Iran. The demantoids from the Ural Mountain mines are the most sought after. The color ranges from yellowish green to an intense green.
Demantoid garnets classically show « horse tail » Byssollite inclusions.
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Garnet - grossulaire: Ca3Al2(SiO4)3
Etymology : from latin "grossularia" = Gooseberry, according to the colour of some crystals.
First discovery : 1811 by Werner.
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Garnet - Malaya:
The commercial name for a pyrope-spessartite garnet coming from Tanzania.
Etymology : Malaya = « prostitute » in ki-swahili.
When these stones were first discovered, no one really knew how to classify them. They were not much in demand and these gems were considered « outcasts » by the miners.

Garnet - Mandarine:Mandarine Garnet - Grenat Mandarin - Namibia ©Gemfrance.com
An orange variety of garnet. Its name evokes a mandarine orange. This name is exclusively reserved for an intense orange variety of garnet coming from north-western Namibia.
At first, this new variety was named "Hollandine" in homage to Holland, a country whose color is orange.
Its intense orange color is due to a high level of manganese.
It’s composition is 85% Spessartite, 12.5% Pyrope and 2.5% Grossular.

Most of the stones are included with Tirodite (a variety of Amphibole). Flawless stones over 1 carat are very rare.
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Garnet - Rhodolite:Rhodolite ©Gemfrance.com
Etymology : from the Greek "rhodon" = rose.
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Garnet - Spessartite: Mn3Al2(SiO4)3Spessartite ©Gemfrance.com
An orange variety of garnet.
Etymology : from the name of Spessart, in Germany.
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Garnet - Tsavorite: ツァヴォライトTsavorite ©Gemfrance.com
A green variety of garnet.
Etymology : from the region of Tsavo Park in Kenya.
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Garnet - Vanadium:Color change garnet - Madagascar ©Gemfrance.com
A variety of garnet with a high content of vanadium which gives it the characteristic of changing color depending on which light source it is viewed under. Some of these gems change from blue to purplish red.
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Gaspeite:Gaspeite ©Gemfrance.com
Etymology : from the name of the locality where it was discovered, Gaspe peninsula, Lemieux township, Gaspe West Co, Quebec, Canada. Discovered in 1966.
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Gem: 宝石
Several definitions are possible. Any stone that can be cut could be qualified as a gem. The majority of gems are mineral species (diamond for example), crystalline aggregates (lapis-lazuli), or rocks (onyx). Organic substances can also be considered gemstones (amber, coral, pearls...). The standard definition of « gem » is based on the qualities of « beauty », « durability », « acceptability », « rarity » although there are numerous exceptions to this. The term « gem » includes gemstones that were formerly called « precious » and « semi-precious».

The terms « pierre précieuse » (Precious gemstone) and « pierre fine » (Fine gemstone) are no longer acceptable terms for use in France following the decree of January 14, 2002.

The term « pierre semi précieuse » (semi-precious gemstone) has been long been forbidden for use in France ; even if its English translation is commonly used ! However, even in English, from a gemmology point of view, the term « semi-precious » is no longer considered correct.

Gemmology:
The branch of mineralogy dedicated to the study of gemstones.
This science requires certain specialized equipment that is needed to identify and study gems. The basic equipment is the 10x (magnification of 10) loupe, and also the refractometer. Others, such as the polariscope, spectroscope, dichroscope, hydrostatic scale and binocular microscope assist in determining the nature of a gemstone and the presence or absence of treatment.
You will find a good description of these pieces of equipment on the website (in French) geminterest ->click.
Other equipment may be needed to identify certain treatments that are applied to some gemstones. Only the laboratories that are specialized in gemstone analysis are equipped with these, due to their high cost (Fluorescence, Diffraction, Raman Spectrometer, UV Spectrophotmeter etc...)

Gibeon:
Name of a meteorite found in Namibia : Great Namaqualand.
The impact field of this meteorite is one of the largest in the world (275 km long) : latitude 25 degrees 20 minutes south, longitude 18 degrees east.
The Gibeon meteorite has been used since antiquity for making tools. Today, it is also used to make decorative plaques due to its unusual structure, knife blades and rings.
When cut, it shows an unusual structure called «Widmanstäten figure ». The phenomena is due to the presence of two different ferronickel alloys.

This meteorite is classified as an octahedrite, (Of), Group IVA, 7.93% Ni, 0.41% Co, 0.04% P, 2.0 ppm Ga, 0.12 ppm Ge, 2.3 ppm Ir.

Gilalite: Chemical Formula/Formule chimique : Cu5 +2 Si6 O17 7H2O
Authors: Cesbron et Williams
Discovery date : 1980
Etymology : From Gila, mine Cristmas, Gila co., Arizona, USA.
Gilalite was also find as inclusions in Quartz.

Chemical properties / Propriétés chimiques Chemical Class/Classe chimique : SILICATES-NC

Subclass/Sous-classe chimique : Silicates non class. - Gibeon Ring:
Rings made from a ferronickel meteorite.
For more information, please see Gibeon.
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Goshenite:Al2Be3(Si6O18)Goshenite ©Gemfrance.com
The white variety of Beryl.
Etymology : its name comes from the place where it was first discovered : Goshen, Massachusetts - USA.
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