Understanding Emeralds: Quality, Purity and the Cat’s Eye
The main component of a gold emerald is alumina crucible, a variety that does not have discoloration or the ‘cat’s eye’ effect. The crystal form is often plate-like, transparent to opaque, with glass to eucalyptus lustre. The colour depends on the amount of iron contained therein, but can be yellow, light yellow, green yellow, brown yellow or similar. The dichroism is obvious, the hardness is 8.5, the density is 3.73 g/cm 3, and the toughness is excellent. There are three famous variants of gold emerald: Alexandrian stone or stone, cat’s eye and stone cat’s eye.
Cat’s eye is a white gold birthstone necklace emerald with a cat’s eye effect. It is rich in colour, such as honey yellow, yellow green, brown green, yellow brown, brown and so on. Among all the gemstones there are many varieties which carry the cat’s eye effect, but only the gold emerald can really be called the true ‘cat’s eye’. The tubular inclusions distributed in parallel in the gemstone crystal can be concentrated and reflected by the curvature, and a light band like a cat’s eye is displayed. When the cat’s eye gemstone is rotated, the light band is opened, like a cat’s eyes, hence the name. Since the best cat eyes are produced in Sri Lanka, it is sometimes called ‘Ceylon Cat Eye’.
The stone cat eye refers to a gold emerald that has both a colour changing effect and a cat eye effect. These are extremely rare, with a clear to strong discoloration effect and a pronounced cat’s eye effect. The value is extremely high.
“Sought-after by collectors”
The processing of gold emeralds is based on the principle of maximising the effect of discoloration and minimising defects. The transparent crown is round and multi-faceted, the pavilion is stepped, and the style is the most common. The cat’s eye effect is processed into a curved surface. The medium-high convex shape and the double convex shape are the most common, mainly to increase the weight of the stone. In addition, in order to make the light band more clear and flexible, the top generally has a high protrusion and the bottom is usually unpolished.
There are many kinds of cat’s eye effects in gemstones, but they are not as precious as gold-green cat’s eyes. Commonly used as a cat’s eye gemstone in imitation, Lezi stone (also known as quartz cat’s eye) is very similar to cat’s eye gemstone, but its hardness is low, it is lighter and the light is weak and unclear. Also called the tiger eye stone, it has obvious linear reflection, but its texture is rough, the light is vague and the flexibility is poor. When the artificial cat’s eye rotates, the curved top reveals two or three bright bands (as opposed to one from the true cat’s eye), the light is dull and the beauty diminished.
Gold emeralds are rarely seen in jewellery stores, and their value is related to weight, colour, transparency and cut. The larger the gemstone particles, the brighter the colour, and the higher the transparency, the higher the value. Among them, the high-transparency green, golden yellow, and sunflower yellow gold emeralds carry the highest price. Golden brown or deeper brown emeralds have a lower price. Diamond emeralds with a diameter of more than 3mm and often honed are sought-after by collectors.
Emeralds remain a worthwhile investment purchase and their beauty and popularity endures.
The highest quality emerald origin – Colombia
The geographical distribution of emeralds is quite diverse. The earliest discovered and mined emerald mine in the world is the Cleopatra deposit in Egypt, but large-scale mining began in 1537 in Colombia, with high yields and quality. Production here once accounted for 80% of the world’s total and about 2 million carats of raw materials were mined. The high-quality emeralds produced by the most famous mining area “Musuo” presented a blue-toned dark green which the gemologist will refer to as “Muzo Green”. The closer gems are to this colour, the higher the price.
Rare: a miracle of one in 5 million
Gemfield, a producer of coloured gemstones, is one of the most advanced, powerful and experienced mining companies in the world. According to Gemfield 5 million carats of ore is mined to get a 1 carat emerald. Emeralds are incredibly rare – and most emerald mines can only cut about 0.5 carats of finished products.
The most important criterion for judging the quality of emerald – colour
The green colour of emeralds determines the value. Too light or too deep a colour and the gem is devalued. Medium green with a beautiful lustre are considered the best. The chromaticity needs to be rich and vivid, with the tone medium to deep medium. Transparency, colour distribution, even a slight chromatic aberration will all have a huge impact on price.
The most demanding element – 100% purity
Although the clearer the gemstone the more precious, natural coloured gemstones will never be 100% pure. Impurities and cracks are characteristics of all natural gemstones. Coloured gemstones mainly rely on their own colour to appeal and gems with numerous and complex cracks are poetically called ‘garden gemstones’. These have many green, tiny, plant-like inclusions – something that reveals gemstones’ natural process of formation.
Appreciation potential – huge
From 2008 to 2018, the net increase of Colombian emeralds was as high as 200-300%, and the growth rate of emeralds has not reached the peak. Emeralds remain expensive, with the price of the big carats even more remarkable. As time goes by and the output becomes scarcer, it is likely that the future prices will rise further.