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Emerald is a chrome-containing beryl. Its color is green and bright, giving people vitality. It has been loved by people since ancient times. Emerald is the birthstone of May, meaning "lucky, happy, opportunity", and diamonds, rubies, sapphires and four precious stones.
Emeralds have a lot of production areas, and the quality is uneven. Synthetic emeralds, optimized emeralds and similar green gemstones are also in the market. Therefore, it is necessary to master the basic identification features.
First, physical and chemical characteristics
Emerald is a chrome-containing beryl with a chemical formula of Be3Al2SiO6. Usually emerald green emerald contains 0.15%~0.30% chromium oxide, and dark emerald green contains 0.15%~0.60% chromium oxide.
However, if it is a green beryl made of iron, it can only be called green beryl, but not emerald. The emerald is a hexagonal crystal system with a hexagonal columnar shape and a hexagonal cross section. Vertically grained transverse stripes are visible on the cylinder surface.
The color is different in shades of emerald green, which can fluoresce under strong light to make the color appear more vivid and transparent. Glass gloss, hardness 7.5, refractive index 1.56~1.59, birefringence
0.005~0.009, density 2.67~2.78g/cm3.
Second, the characteristics of the naked eye identification
(1) Emerald
Natural emeralds are produced in many places, and high-quality emeralds are mainly produced in Colombia and Zambia. The main identification characteristics of emeralds from different regions are as follows:
1. Colombian emerald
Colombia is the world's largest producer of quality emeralds. The emeralds produced are transparent emerald green, pale green, and bright and pure. The gemstones are visible to the naked eye with some anti-white light healing fracture surfaces and white calcite or black carbon inclusions. A sawtooth type gas-liquid-solid three-phase fluid inclusion can also be seen by observing with a 20x magnifying glass. A translucent brown short columnar fluorocarbon calcium strontium ore inclusion is sometimes seen.
2. Zambia produces emeralds
Zambia is the second largest producer of quality emeralds in the world. The emeralds produced are green, blue-green and dark green, with bright colors but slightly grayish and pure. The gemstone may contain flaky biotite or columnar hornblende inclusions under the naked eye or 10~20 times magnifying glass.
3. Brazilian emeralds
The emeralds produced in Brazil are dark green, yellow-green, with a dull color and poor transparency. They are low-grade emeralds. The gemstone contains a white cloud-like calcite, an albite inclusion, a black flaky biotite and a granular magnetite inclusion, and a layered spread of a droplet-shaped gas-liquid inclusion under the naked eye or a 10-20 magnification magnifying glass. .
4, Russia Ural Emerald
The emeralds produced in Russia's Ural are yellow-green and have a dull color. The gemstone contains 10% biotite and bamboo-like anomalous inclusions under the naked eye or 10~20 times magnifying glass.
5, Indian emeralds
Indian emeralds are yellow-green and have a dull color. The gems in the naked eye or 10 to 20 times magnifying glass often contain two sets of scale-like biotite inclusions that are perpendicular to each other.
6, Tanzanian emerald
The emeralds produced in Tanzania are comparable to the emeralds produced in Colombia. They are usually green with a yellowish or blue tint, but the particle size is generally small and can be used as a raw material for jewelry.
7, Madagascar emerald
The emeralds produced in Madagascar are light blue-green and brighter in color. The interior of the gem is relatively clean, with few defects, and occasionally a needle-like inclusion.
8, China's Yunnan emerald
China's Yunnan emeralds are rich in color, with dark green, green, blue-green, yellow-green, light green, etc., and the transparency is generally poor. Due to the association with tungsten-tin ore, the emerald ore body is small in size, and there are fewer high-quality emeralds in dark green and transparent. High-quality emeralds, solid inclusions such as black needle-shaped tourmaline, flaky mica, platy feldspar and granular arsenopyrite, and gas-liquid inclusions can be seen under the naked eye or magnifying glass.
In recent years, the brilliant green high-quality small-grain emeralds produced in Pakistan and Afghanistan are beautiful and very popular.
(two) synthetic emerald
Synthetic emeralds have a history of a hundred years, and the more mature methods are flux growth method and hydrothermal method. Since the temperature and pressure conditions for the formation of synthetic emeralds are similar to those of natural emeralds, they must be carefully observed during identification.
1. Flux growth method for synthesizing emerald
The flux growth method synthesizes emeralds in bright colors without yellow or blue tones. The red fluorescence effect of the emerald-synthesized emerald is more pronounced than that of the natural emerald. It is placed on the black base plate in the dark, and the red light that the pan-natural emerald does not have is illuminated with strong light. There are many inclusions inside the gemstone, and the milky white smoke-like or feather-like flux inclusions are visible to the naked eye, and are transmitted into the water to transmit light. The inclusions are brownish yellow. In addition, hexagonal or triangular platinum sheets and hexagonal columnar wollastonite inclusions are also visible. No visible healing of the cracked surface in natural emeralds.
2, hydrothermal synthesis of emerald
The hydrothermal method synthesizes emerald transparent, uniform color, and is greenish or microstrip blue or yellow green. Place the red light on the black base plate in the dark with strong light. The interior is clean and there is no flux growth method to synthesize the aerosol-like flux inclusions and gas-liquid inclusions of emerald. A number of small dots or spikes spread over one level can be observed with a 10x magnifying glass. Occasionally, you can see a crystal sandwich with a different shade of color, but a straight spread. Under the high magnification magnifying glass, a tubular inclusion body oriented in parallel and a nail-shaped inclusion body composed of columnar silicon vermiculite and liquid can be seen.
3. Synthetic emerald coated beryl
The polished beryl is placed in a hydrothermally synthesized emerald solution to give the beryl surface an emerald shell with a thickness of about 0.5 mm. This coated beryl is placed in the water and is darker in color. In addition, interlaced network cracks are visible at the junction of the coating and beryl. In addition, the interior of the beryl is generally cleaner, and the type of inclusion differs from the natural emerald.
(3) Optimizing emeralds
When emeralds have more healing fracture surfaces that reduce the clarity of the gemstones, merchants often use oil filling methods to make up for them. The surface of the gemstone has a crack that opens into the interior. Under the 10x magnifying glass, the color reflection phenomenon can be seen at the oil filling. Put the oiled emerald in the vicinity of the incandescent lamp, the oil beads will seep out from the crack, and the oil will be wiped with a clean white paper.
(4) The difference between emeralds and similar green gemstones and imitations
There are not many transparent, bright green gems similar to emeralds. There are only five kinds of commercially available only calcium garnet, fluorite, apatite, jade, and chrome diopside. Adding imitations such as artificial garnet and imitation emerald glass, their main physical characteristics are shown in Table 1.
Table 1 Main physical characteristics of emeralds and similar green gemstones and imitations
Gem name hardness density (g/cm3) refractive index birefringence
Emerald 7.5.2.37~2.781.564~1.6020.005~0.009
Green calcium aluminum garnet 6.538.451.740
Green jade 73.331.66~1.680.014
Green fluorite 43.181.430
Chrome diopside 53.301.67~1.700.025
Light blue green apatite 52.9~3.11.632~1.6670.002~0.005
Green tourmaline 73.061.62~1.640.018
Beryl molten glass 72.471.520
1, calcium aluminum garnet
Calcium aluminum garnet is generally yellow-green, with traces of chromium and vanadium will be emerald green, very similar to emerald. However, the garnet has a stronger luster than the emerald, and the surface is as bright as the grease. The gemstone has less inclusions and a larger specific gravity.
2, fluorite
Green, pale green fluorite, similar in color to emeralds of lower quality. However, the gloss is weak, the interior is clean, and no inclusions are visible to the naked eye. The hardness is only 4, which can be infused with glass.
3, apatite
A microstrip blue-lighted green apatite produced by Madagascar, similar in color to emerald. However, there are few inclusions in the apatite, the surface is greased, the hardness is 5, and it can be scored with a knife.
4, jade
The color of the high-quality jade is green, but the transparency of the jade is poor. Even the most transparent jade can be seen in the flocculent fibrous structure.
5, chrome diopside
A chromium-containing diopside made in Russia, the color is pure green, also known as Russian emerald. However, this diopside has few inclusions and a large birefringence. When viewed from the countertop with a magnifying glass, the bottom edge double shadow is visible. Hardness 5, can be scored with a knife.
Chrome diopside
6, artificial garnet garnet
Adding traces of chromium to the artificial garnet will give you a bright green color to emerald. However, its color is dull, the gloss is bright, and the red light is illuminated by the hand in the dark. The density is high and the interior is very clean.
7, molten beryl glass
The light-colored beryl is ground into a powder, and a small amount of chromium oxide is added and then heated and melted to prepare a beryl glass having a chemical composition similar to that of emerald but not crystallized. The density is lower and the refractive index is lower than natural emerald. There are few internal defects in the gemstone, and mineral inclusions in natural emeralds are not seen.
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