Emerald - Encyclopedia

    Class : Silicate
    Subclass : Cyclosilicate
    Crystal system : Hexagonal
    Chemistry : Be3 (Al, Cr3+, V3+)2 Si6O18

    Rarity : Rare

Emerald is a green variety of beryl, colored by chromium or vanadium, and this is the second gem in terms of value, behind the diamond. Its name comes from the ancient Greek "smaragdos" deformation of the Persian word "Zamarat" which means "heart of stone". It was already a currency exchange in ancient times and it was also widely exploited in Egypt in the Cleopatra's Mines (Jebel Zabarah) which provided only bad quality crystals. Beryllium, chromium and vanadium are uncommon chemical elements, which explains the rarity of the emerald in nature. Its environment of crystallization is very different from beryl, it occurs in micashistes with biotite in Urals or in hydrothermally altered limestone in Colombia (where it sometimes filled oldest fossils of snails cavities). It is always in association with ultrabasic rocks that provide chromium and vanadium. We can also highlight its very punctual presence in pegmatites where its quality is still poor. It gives mostly prismatic and elongated hexagonal crystals but rarely terminated. It is a mineral species only used in jewelery.

Emerald in the World

The finest crystals come from the Muzo area in Colombia. These deposits have been exploited since the sixteenth century, the emerald crystals (up to 8 cm) are present in calcite veins that run through bituminous limestone (picture in margin). The second deposit of global interest is the Central Urals in Russia. Crystals are lower quality than the Colombians, but they can be much larger : about 40 cm ! Other good specimens come from Zimbabwe (crystals generally small in sizes) and Brazil where green vanadium beryl are considered as emeralds since the 60's. Also note a deposit recently discovered in China, in Pingwu area in the  Sichuan Province.

Emerald in France

In France emerald is not present, the sites that can sometimes encounter described in the ancient books are related to misidentification, note that the real emerald can be easily confused with other beryl varieties such as aquamarine that can take pale green hues.

Twinning

There are no twinned emerald, just like beryl. Specimens called "trapiches" are varieties of crystals showing six rays growth characteristics. Each face of the hexagonal prism is extruded to form a wheel. These crystals are particularly sought by collectors and often very expensive. They are also shaped to integrate pieces of jewelry.

Fakes and scams

Scams around the emerald are numerous. The most common and concerning 95% of emeralds is oiling (GIA data). Often fractured, crystals are placed under vacuum and fracture planes are injected with oil, sometimes colored, this in order to improve the transparency and color of the stone and hide fragility. This practice is performed on both cut stones as rough crystals. This is why it is not recommended to clean emeralds in ultrasonic bath which could fly the stone chips... Over time, being worn and exposed to light, oil turns yellow and escapes from fractures, can totally ruin the look of the specimen. Just browse jewelers to find that this treatment is almost never specified...

You should also know that emeralds are now synthesized in laboratory, although inclusions are characteristic, it is sometimes very difficult to differentiate a natural emerald and a synthetic, besides some authentication means based on isotopic analyzes of oxygen content in the structure of the mineral... Synthetic emerald specimens are found in the mineral market today, as so-called "Chatham" emeralds (photo in margin). This specimen was sold as "Chatham emerald unoiled" on eBay over 800 € and without the word "synthetic" nowhere ...

Finally, the latest scam listed, it is the sale of materials such glasses or plastics as emerald, again for gemstones or rough...



Hardness : 7,5 to 8
Density : 2,6
Fracture : Conchoidale
Trace : White




TP : Transparent to translucent
RI : 1,560 à 1,602
Birefringence :  0,006 to 0,009
Optical character : Uniaxial -
Pleochroism : Very weak
Fluorescence : None


Solubility : Hydrofluoric acid, sodium or potassium hydroxide

Magnetism : None
Radioactivity : None