Emerald is a kind of beryl containing chromium. It has a bright green colour and is full of vitality. People have loved it since ancient times. Emerald is the birthstone in May, which means “luck, happiness and opportunity”.
Natural emeralds are produced in many places, and high-quality emeralds are mainly produced in Colombia and Zambia. Because emeralds are made in many places and have different quality, there are many synthetic emeralds, optimized emeralds and similar green gemstones in the market. Therefore, it is necessary to know the essential identification characteristics.
Characteristics of emeralds:
Emerald is a kind of beryl containing chromium, and its chemical formula is be3al2sio6. Generally, emerald emeralds contain 0.15% – 0.30% chromium oxide, and dark emerald emeralds contain 0.15% – 0.60% chromium oxide. However, if green beryl is colored by iron, it can only be called green beryl, not emerald. Emerald belongs to the hexagonal crystal system; the crystal is hexagonal columnar, the cross-section is hexagonal, and the vertical grain can be seen on the cylindrical surface. The colour is emerald green with different shades, which can emit fluorescence under a strong light to make the colour more bright and transparent. Glass lustre, hardness 7.5, refractive index 1.56-1.59, birefringence 0.005-0.009, density 2.67-2.78g/cm3.
The main identification characteristics of emeralds from different origins are as follows:
1. Columbia Emerald
Colombia is the largest producer of high-quality emeralds in the world. The emeralds produced in Colombia are transparent emerald green, light emerald green, bright and pure in colour. Visible to the naked eye, some anti-white healing fracture surfaces and white calcite or black carbonaceous inclusions in the gem.
2. Zambian Emerald
Zambia is the second-largest producer of high-quality emeralds in the world. The emeralds produced in Zambia are green, blue-green and dark green, with bright colour but slightly grey and pure. The naked eye or under a magnifying glass of 10 to 20 times reveals that the gem contains flake biotite or columnar hornblende inclusions.
3. Emeralds from Brazil
Emeralds from Brazil are dark green and yellow-green, with dim colour and poor transparency, belonging to low-grade emeralds. It can be seen by the naked eye or 10 ~ 20 times magnifying glass that there is white cloud-like calcite and albite inclusions, black flake biotite and granular magnetite inclusions, and layered droplet like gas-liquid inclusions in the gem.
4. Russian ural Emerald
The emerald produced in Ural of Russia is chrome diopside. Russian emerald is just a good name, and it is also called “Siberian Emerald” in Russia. It is yellowish-green in color. It can be seen by the naked eye or 10 ~ 20 times magnifying glass that there is flake biotite and bamboo-like actinolite inclusions in the gem.
5. Indian Emerald
Emeralds from India are yellowish-green in colour. It can be seen by the naked eye or 10 ~ 20 times magnifying glass that there are two groups of scaly biotite inclusions in gemstones.
6. Tanzania Emerald
The emeralds from Tanzania are comparable to those from Colombia. They are usually green with a slightly yellow or blue tone, but the particle size is generally small, so few emeralds can be used as jewelry raw materials.
7. Emeralds in Yunnan, China
Emeralds are produced in Yunnan Province of China. They are rich in hues, such as dark green, green, blue-green, yellow-green, light green, etc. The transparency is generally poor. Because it is associated with tungsten and tin ore, the scale of the emerald ore body is small, and there are few dark green transparent, high-quality emeralds.
The synthesis of emerald has a history of one hundred years, and the more mature methods are the flux growth method and hydrothermal method. Since synthetic emeralds’ formation temperature and pressure conditions are similar to those of natural emeralds, we should pay attention to the identification.
1. Synthesis of emerald by flux growth method
The colour of emerald synthesized by flux growth method is bright but without yellow or blue hue. The red fluorescence effect of synthetic emerald by flux growth method is more evident than that of natural emerald. It is placed on the black floor in the dark place, and the red light, which is not found in Pan natural emerald, is illuminated by strong light.
Residual flux in the synthesis of emerald by flux growth method
There are many inclusions in gemstones. Naked eyes can see milky white smoke or feather-like flux inclusions. When put into water and transmitted by light, these inclusions are brown-yellow.
In addition, we can see the hexagonal or triangular platinum flakes and hexagonal columnar beryllite inclusions but can not see the reflective healing fracture surface in natural emerald.
2. Hydrothermal synthesis of emerald
Emerald raw material synthesized by hydrothermal method
Hydrothermal synthesis of emerald is transparent and uniform in colour, showing brilliant green or a little blue or yellow-green. Please put it on the black base plate in the dark place, and irradiate the red light with strong light. The interior is clean, and there is no smoke like flux inclusion and gas-liquid inclusion like emerald synthesized by flux growth method.
Hydrothermal synthesis of inclusion of emerald
With a 10 times magnifying glass, we can see many dots or nails on one layer. Occasionally, we can see different colours but the flat distribution of microcrystalline interlayer. Under the high magnification, we can see the directional parallel arrangement of tubular inclusions and the nail like inclusions composed of columnar beryllite and liquid.
3. Synthetic emerald coated beryl
The synthetic emerald coating of beryl is to put the polished light colour beryl into synthesizing emerald by the hydrothermal method. A layer of the emerald shell with a thickness of about 0.5mm is formed on the surface of beryl. This kind of coated beryl is dark in the water. In addition, it can see interlaced network cracks at the junction of coating and beryl. In addition, the interior of beryl is generally clean, and the inclusion type is different from that of natural emerald.
Comparison of emerald before and after optimization
When emeralds have many healing fracture surfaces that can reduce the clarity of gems, the merchants often use oil injection to make up for them. There will be cracks on the surface leading to the inside. Under the 10 times magnifying glass, colour reflection can be seen at the oil filling place. Put the oiled emerald near the incandescent lamp to bake, the oil beads will seep from the cracks, and there will be oil stains when wiping with clean white paper.
Differences between emeralds and similar green gemstones and imitations
There are not many transparent and bright green gemstones similar to emeralds. There are five kinds of gems with commercial significance: almandine, fluorite, apatite, jadeite, and chromite diopside. In addition, artificial yttrium aluminium garnet fused beryl glass and emerald are easy to be confused.
Grossular is generally yellowish-green, containing trace amounts of chromium, and vanadium will be emerald green, very similar to emerald. However, the lustre of almandine is stronger than that of emerald. The surface of almandine is as bright as oil. There are fewer inclusions in the gemstone, and its specific gravity is larger.
Green and light green fluorite are similar to poor quality emerald in colour. But the lustre is weak, the interior is clean, can see no inclusions with naked eyes, and the hardness is only 4, which can be engraved with glass.
Malagasy apatite having a bluish tinged greenish hue similar to emerald. However, the apatite has few inclusions, and its surface is glossy with oil. The hardness of apatite is 5, which can be carved with a knife.
The colour of high-quality jadeite is green, but the transparency of jadeite is poor. Even the most transparent jadeite can see a flocculent fibrous structure.
5. Chrome Diopside
Chrome diopside produced in Russia, the colour is pure green, also known as Russian emerald. However, there are few inclusions in diopside, and its birefringence is high. When viewed from the table with a magnifying glass, we can see the double shadow of the bottom edge. The hardness of the diopside is 5, which can be carved with a knife.
6. Synthetic yttrium aluminiumgarnet
Adding a small amount of chromium to synthetic yttrium aluminium garnet will present bright green to imitate emerald. However, its colour is dull and bright. In the dark, the flashlight is used to irradiate the red light. The density is large, and the interior is very clean.
7. Molten beryl glass
The light coloured beryl is ground into powder and then heated and melted by adding a small amount of chromium oxide to make beryl glass with a chemical composition similar to emerald but without crystallization. The density is small, and the refractive index is lower than that of natural emerald. There are few internal defects in gemstones and no mineral inclusions in natural emeralds.
The six “most” of Emeralds
1. The best quality emerald origin — Colombia
The distribution of emeralds is not unique and has been found in many countries. The earliest emerald mine discovered and mined in the world is the Cleopatra deposit in Egypt. But the real large-scale mining was in 1537 in Colombia, South America, with the highest production and the best quality, accounting for 80% of the world’s total production, about 2 million carats of emerald raw materials.
In addition, Zambia and Zimbabwe in Africa, Australia of Australia, South America’s Brazil and other countries and regions have produced, but the quality can not be compared with Colombia emerald.
2. The most important factor affecting price — the scarcity of output
Although emeralds are produced in many parts of the world, the output of high-quality emeralds is still far lower than that of diamonds of the same quality. It can be said that only one emerald in every 1 million beryl minerals is emerald. Emeralds are brittle and easy to crack in the process of mining. The rare things are precious make emeralds challenging to be mined and rare in output, a well deserved rare gem, ranking first in the value of imported coloured gems from the United States.
3. The most important standard to judge the quality of emerald– colour
Emerald green colour determines its value; too shallow or too deep is not good; medium green with beautiful lustre is the best. The colour is thick to bright, and the colour is medium to deep. Good transparency and uniform color distribution. Even a slight colour difference can have a huge impact on the price.
It is generally believed that the emeralds produced in the most famous Chivor and Chivor mining areas in Colombia will be slightly bluish. This kind of emerald is regarded as the best emerald in quality. If it also has the characteristics of good cleanliness, it is perfect.
4. The least demanding factor in choosing emeralds: 100% purity
Although the clearer and more precious the emeralds are, the more transparent the emeralds are, the impurities in the emeralds are easy to be seen. This visible flaw is a basic basis for identifying “natural” gems.
Natural colored gemstones will not be 100% pure. Impurities and cracks are the characteristics of all-natural gemstones. Coloured gemstones are mainly won by their colours—the requirements of purity not the same as the evaluation standard of diamonds.
5. The best cutting method of emerald — “Emerald cutting”.
In the past, emerald cutting was mainly used for emeralds to reduce the huge pressure formed during cutting to protect gemstones. Nowadays, this problem is not very important in modern cutting technology, which is widely used in many types of gems. “The number of facets cut by the emerald cutting method is about 50. Emerald cuts are viewed from the top like a rectangle with corners cut off. With the stepped facet, it can become a very beautiful gem.
6. The basic standard for emeralds to have the most investment potential — the size is more than 1 carat
A high-quality emerald of the same size as a diamond has a much higher price than a diamond. Emeralds are mostly small particles, generally less than 1 carat. If the quality of emerald is excellent and can reach more than 1 carat or even more than 2 carats, it is already very precious, and the price will be surprisingly high.