Nowadays, many people use synthetic emeralds to make huge profits by using fake emeralds to confuse the real ones. It is difficult to distinguish natural emeralds from synthetic emeralds.
It is because: (1) the existence of growth bands and multiphase inclusions in gemstones is generally an important feature of natural gemstones. This phenomenon is seen in some synthetic emeralds. The existence of bubbles is generally an important feature of synthetic gemstones.
② The characteristics of emeralds produced all over the world are quite different.
③ The characteristics of synthetic emeralds produced by different methods are also different. Therefore, in identifying emeralds, we must consider the characteristics of emeralds and the interference of various factors to reduce the mistakes.
From the perspective of discrimination, natural emeralds can be divided into two types.
(1) American type: including emeralds from Colombia, Brazil, and the United States. It is characterized by low refractive index, low density, ultraviolet (long wave, the same below) irradiation fluorescence; with Charles filter observation, the color turns red.
(2) African emeralds, including Zimbabwe, South Africa, Zambia, Tanzania, India, and Pakistan. It is characterized by a high refractive index; High density; Ultraviolet radiation generally does not emit fluorescence, and it is green and grayish-green when observed with a color filter.
From the perspective of synthesis, synthetic emeralds can be divided into two categories.
(1) common synthetic emeralds: emeralds synthesized by Chatham method, Zellfass method, Gilson method, Linde method, Lennox method, and Reagan method. It is characterized by low refractive index, low density, and bright red fluorescence under ultraviolet irradiation; The color changes to bright red through a color filter
(2) the rare synthetic emerald, i.e., Gilson n-type, is a flux method with iron added, which has stopped production. A high refractive index characterizes it, high density, no fluorescence under ultraviolet irradiation. The color is green and grayish-green when observed with a color filter.
We can divide the distinguishing marks of emeralds into three groups
1. Discrimination of fluorescence and color filter observation
The two characteristics of emeralds are roughly related: those with fluorescence turn red under the color filter; The color of those without fluorescence remained unchanged under the color mirror. Generally speaking, it is a common feature of synthetic emeralds that they emit bright red fluorescence under ultraviolet irradiation and show bright red under the color filter. Generally speaking, this is the characteristic of American natural emerald. It may be American emerald or common synthetic emerald if it emits pink fluorescence under ultraviolet radiation and is pink when observed by a color filter. At this time, two other groups of characteristics should be used to distinguish.
It does not fluoresce under ultraviolet irradiation and is green or grayish-green when observed with a chronoscope. It is generally the characteristic of African-type natural emeralds. Still, it may also be a rare synthetic emerald (Gilson n-type). At this time, the other two kinds of emeralds should be used.
Group characteristics. In addition, there is an absorption band at 427 nm in the purple region, which is the characteristic of Gilson n. type emeralds. This absorption band has never been seen in natural emeralds. It should be noted that some Russian emeralds turn red with a color filter.
2. Discrimination of refractive index and density
The refractive index of emerald has a positive correlation with density. The density is high; the refractive index is high; the density is low, the refractive index is low. The refractive index is greater than 1.580. The density is greater than 2.70 (g c/ m), which is the characteristic of natural emerald. The refractive index is less than 1.566. The density is less than 2.67 (G C / M), which are the characteristics of synthetic emerald. Suppose the refractive index and density are between the above two values. In that case, it is uncertain whether it is furan emerald or synthetic emerald. At this time, it needs to rely on the other two groups of characteristics to distinguish. The density can be determined quickly by preparing 2.67 and 2.70 heavy liquids.
3. Discrimination of inclusion
Bubbles, two-phase inclusions, and three-phase inclusions exist in natural and artificial emeralds, which can not be used as a basis for discrimination. Solid inclusions, such as pyrite, calcite, calcite, and chromite, are American-type natural emeralds’ characteristics. Solid inclusions, such as biotite, actinolite, and tremolite, are the characteristics of African-type natural emeralds. Solid inclusions, such as peridot (colorless and transparent triangular biconical or nail-like), platinum flake (bright silver-white)
Opaque triangle or hexagon) and smoky inclusion is the characteristics of synthetic emeralds. However, it should be noted that peridotite has also been found in the emeralds of Pakistan, so we can not draw a conclusion based on the inclusion of peridotite alone. Finally, we talk about the finished product of coated emerald, which is light-colored natural beryl inside and coated with a thin layer of synthetic emerald on the surface. The characteristics of the emerald coating are as follows: 1. The edge is dark green with strong fluorescence. The middle color is slightly lighter, and the fluorescence is slightly weak; ② The surface is poorly polished, with reticular cracks (observed with a magnifying glass). ③ there are characteristic inclusions of natural beryl, such as biotite, pyrite, and tubular bubbles.