Emerald Stone – Characteristics, Varieties and Quality

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Emerald is actually a variation of green beryl, the colour of which appears due to an excess of chromium.

Like emerald, Aquamarine, Heliodorus and Morganite are a variation of beryl (mineral species) with the formula Be3Al2(Si6O18). Hardness of 7.5 – 8 mohs.

Beryls are usually found with a special glassy, transparent sheen. The pure stone is colourless, but because of the tints of other elements, it can appear in blue, yellow, red, white and green.

The emerald  crystallises in the hexagonal system and its green hue varies from medium to dark green, depending on the percentage of chromium oxide (0.1 – 0.3%). A gem containing less than 0.1% chromium oxide is considered to be just green beryl, not an emerald.

Emerald Stone
Rough emerald stone

There are deposits in different parts of the world, and each region provides emeralds with its own peculiar characteristics.

Their economic value is also labelled, with Colombian emeralds having the highest value.

The first emerald mines appeared in Egypt, but there is no longer any production in that country. It was already commercialised two thousand years before Christ, in Babylon, but it was rare until the Renaissance, when South American deposits were discovered.

Pedra Esmeralda - Caracteristicas, Variedades e Qualidade

Today the emerald is produced mainly in Colombia, Zambia, Zimbabwe, Tanzania, Madagascar and Brazil (Goiás, Bahia and Minas Gerais).

The emerald is considered one of the 4 most precious stones in the world, along with the Ruby, the Diamond and the Sapphire. It is a very valuable stone and one of the oldest ever found.

Main Gems and Precious Stones
Main Gems and Precious Stones

Emeralds are rarer and even more expensive than diamonds, depending on their quality. But they are the rarest of all gems, which is why they often have higher values than diamonds.

The best quality emeralds, with 5 to 8 carats, can be worth up to US$ 5,600 per carat. Gems of the same weight with average quality range from US$ 100 to US$ 580 per carat.

Emeralds have been commercially synthesised since the 1940s. Unlike other minerals, all synthetic stone production is destined for the jewellery industry.

Emerald can be confused with synthetic emerald, chrome-diopside, chromolite, Paraiba tourmaline, tsavorite, demantoid, uvarovite, composite gems, glass, plastic-covered beryl and diopside.

See Identifying a gemstone or precious stone is a difficult task.

Characteristic of the emerald stone
Characteristic of the emerald stone

Names of emeralds used on the market

  • Colombian – the market name for high-quality emeralds.
  • Russian or Siberian – name for the less bluish with more inclusions and lighter colour than Colombian gems.
  • brasileira – term sometimes used for light green coloured gems.
  • sandawana – term used for deep green gems, usually small in size and with many inclusions.
  • da Zambia – term used for slightly greyish gems.

Possible emerald treatments

  • filling fractures or surface cavities with a hardening substance (good stability).
  • impregnation – with oils, waxes, resins or colourless plastics, not hardened, in fractures or cavities, to improve appearance (medium to good stability)
  • dying – with dye or coloured oil (detection: the dye concentrates in the cracks).
  • it is possible to eliminate traces of yellow, if they are due to additional iron content, by heat treatment at temperatures between 400 and 450°C.

Emerald Quality Factors

The gem has many special qualities, but professionals agree that they are above all about colour.

Emerald Stone
Emerald Stone

Especially for the standard of green. And knowing how to differentiate between emerald values requires a well-trained eye, as you have to recognise sometimes subtle variations that make it worth more.

There are therefore four factors that make up the quality of the emerald, which are:

1. Colour

From light to very dark green to a very strong bluish green.

The most desirable colours are bluish green to pure green, being well coloured but not dark, as the most valued are the transparent ones.

Its colour is uniform and intense, unmatched by anything else in nature.

And if it has a very yellowish or bluish hue, the stone is a different variety of Beryl, and so its value drops accordingly.

Chromium, vanadium and iron are the trace elements that cause the emerald’s colour. The presence or absence of each and their relative quantities determine the exact colour of an emerald crystal.

2. Clarity

From transparent to translucent.

Emeralds contain inclusions that are visible to the eye, without the need for equipment, which is why some traders and consumers understand and accept the presence of inclusions. Clean emeralds are more valuable because they are rarer.

But when inclusions interfere with the transparency and clarity of the stone, it has a negative effect on the trade, and thus drastically reduces its value;

3. Cutting

The person cutting must consider the depth of colour, durability and inclusions of the rough when cutting. And mistakes when cutting can cause weight loss, which reduces the value of this jewel.

Emeralds already have significant natural fractures, so the cutter must design the cut to minimise the effect of these fractures on the stone. Another important factor is that emeralds are very fragile, making them vulnerable to damage during the procedure or in careless daily use.

As well as taking care with the type of cut that will be made, as it can change the tone and saturation of the stone, leaving a darker pale stone with a deep cut, or even a less faceted one leaving the stone lighter with a shallow cut.

4. Kilometres

Quality for quality, the price of an emerald can rise dramatically as the size increases. Therefore, in jewellery shops, prices will vary greatly depending on the carat of the emerald.

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