Emerald is a natural mineral ranging in colour from light to dark green. It crystallises in the hexagonal crystal system and belongs to the beryl family. Emeralds are less dense and stable than other beryl varieties, ranking 7.5 on the Mohs scale of mineral hardness. For this reason, they are usually step-cut in a square or rectangular shape with cut-off corners (an emerald cut) to protect the fragile stone. This cut also accentuates the bright green colour.
COLOUR, A FACTOR IN DETERMINING VALUE
The most important factor in determining the value of an emerald is its colour. The more intense the green, the more precious the gem. Another factor that can raise the value of an emerald is its clarity, which is defined by its inclusions (flaws or imperfections inside and sometimes reaching the surface) because it is a way of confirming that it is natural and also indicates where it was mined. It is rare for an emerald to have no imperfections and inclusions, and when one is found it is considered suspicious and is thoroughly examined.
TREATMENTS TO ENHANCE THE QUALITY OF THE EMERALD
Like all gemstones, emeralds undergo treatment to enhance their quality. Some of these treatments are accepted worldwide and others not. They can be oiled, for example, to fill cracks or fissures
The oil enters the stone through surface-reaching cracks, improving the clarity and colour of the emerald. This is the most widespread treatment, although the effect is not permanent. It is universally accepted, as most natural emeralds have undergone the process. It is necessary to know the amount of oil used for each stone, since more oil means better clarity, and better clarity means a higher value. Over time, however, the oil evaporates and the gem’s appearance changes dramatically. Emeralds that have not been oiled are quite rare, and their price differs greatly from treated gemstones.
Other kinds of impermanent treatment include the use of resin to fill cracks and fissures, or the coating of the gem with a thin coloured or transparent film. Whatever the treatment, it must be reported before any purchase, because the value of a stone that has not been treated can be very high.
Colour treatment through irradiation is permanent, but even so, it must be reported.
Synthetic stones are often used as an alternative to mineral stones. They are not mined, having been created in a laboratory by human beings, but have the same chemical composition, structure and physical properties as the naturally occurring mineral. The differences usually lie in the inclusions of the natural minerals or in their absence.
There is a great difference in value between mined and synthetic stones, since the one is a material that occurs in nature, while the other comes from a lab. Every mineral stone is unique, from its external appearance, including the natural colour, to the internal characteristics that define it.
Synthetic stones look more like mass produced products, usually having a similar colour and a high degree of clarity.
Because they are much less valuable than mineral stones, they are more often used in silver jewellery and rarely in gold.
THE IMPORTANCE OF COUNTRY OF ORIGIN
One important factor in mineral stones is their country of origin, because it essentially defines their identity. This can be determined from the inclusions inside the gems. Sometimes, the nature of the inclusions in combination with the colour of the stones can immediately indicate where they come from, even down to a specific mine.
THE USE OF THE GEM REPORT
A gem report, including all the details necessary to determine the value of the stone, is always necessary. As noted above, the value of a treated and an untreated gemstone can vary widely. All stones must be accompanied by a gem report to protect both the seller and the buyer.