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The mineral name of emerald is beryl, which is the most important and precious variety of beryl and is known as the “king of green gemstones”. It is regarded as one of the “five great treasures” given to mankind by nature, along with diamonds, rubies, sapphires and cat’s eyes. Emerald is verdant and pleasing to the eye. As the birthstone of May, its color represents the arrival of spring.

So, how do you distinguish between natural emeralds, optimized emeralds, synthetic emeralds and imitation emeralds? If you have a batch of beautiful green gemstones (as shown in Figure 1), how do you accurately identify the natural emeralds, optimized emeralds, synthetic emeralds and imitation emeralds?

Figure 1 : Emerald and its imitations

1. Identification methods

First, use a refractometer to detect the refractive index of the gem (Figure 2). The refractive index of emerald is: 1.577~1.583 (±0.017). Imitation emerald can be excluded by detecting the refractive index.

Figure 2 : Testing the refractive index of emerald (see test data on the left)

Test results:

Group A：1.58(By spot test method);

Group B：1.577~1.583;

Group C：:1.545；

Group D：1.577~1.583。

Through the refractive index test, it can be seen that the refractive index of group C gemstones is not within the refractive index range of emeralds and can be ruled out. The remaining three groups of suspected emeralds, A, B, and D, continue to the next step of testing (Figure 3).

Figure 3 : Three groups remaining after excluding imitation emeralds

2.  Use a gem polariscope to detect the optical characteristics of emeralds

Emerald has four bright and four dark phenomena under polariscope, and has a uniaxial crystal interference pattern. Test the three groups A, B, and D separately (Figure 4, Figure 5)

Figure 4 : Using a polariscope to detect the optical characteristics of emerald (the left side shows the four bright and four dark phenomena)

Figure 5 : Using a polariscope and a conoscope to detect the axiality of emerald (the left side is a uniaxial crystal interference pattern)

Test results:

Group A：Four bright and four dark, Heterogeneous, uniaxial crystal;

Group B：Four bright and four dark, Heterogeneous, uniaxial crystal;

Group D：Four bright and four dark, Heterogeneous, uniaxial crystal;

From the test results, it can be seen that the three groups ABD all meet the test data of emerald and need to be tested further.

3.  Use a calcite dichroscope to observe the pleochroism of the gem (Figure 6).

The pleochroism of emerald is mediumto strong, blue-green and yellow-green.

Figure 6 : Observing the pleochroism of emerald using a dichroscope (observation phenomenon on the left)

Test results:

Group A：medium pleochroism, blue-green, yellow-green;

Group B：strong pleochroism, blue-green, yellow-green;

Group D：medium pleochroism, blue-green, yellow-green.

From the test results, it can be seen that the three groups ABD all meet the emerald’s pleochroism test data and need to be tested further.

4.  The absorption spectrum of emerald detected by gem spectroscope (Figure 7) shows that emerald mainly shows the absorption line of chromium.

In the red area, there are strong absorption lines at 683nm and 680nm, and weak absorption lines at 662nm and 646nm; there are partial absorption bands between 630-580nm in the orange-yellow area; and there is full absorption in the purple area.

Figure 7 : Detection of the absorption spectrum of emerald (the figure below shows the observed phenomenon)

Test results:

Group A：Absorption lines of chromium;

Group B：Absorption lines of chromium;

Group D：Absorption lines of chromium;

From the test results, it can be seen that the three groups of ABD all meet the absorption spectrum test data of emerald, and further testing is needed.

5.  Use a microscope to magnify and examine the emerald (Figure 8).

Natural emeralds can be observed to have natural mineral inclusions, such as solid mineral inclusions, fluid inclusions, cavities, negative crystals, color bands, three-phase inclusions, etc. Synthetic emeralds can be observed to have wavy growth lines, flux residues, nail-shaped inclusions, etc. Fillings, dyes, etc. can be observed in optimized emeralds.

Figure 8 : Identification features of emerald observed using a microscope

Test results:

Group A（Figure 9,Figure 10）

        Figure 9 : Yellow-brown oil surrounds irregularly shaped mineral inclusions

Figure 10 : Green oil and mineral inclusions

From the observed phenomena, it can be seen that group A is optimized emeralds.

Group B（Figure 11,Figure 12,Figure 13）

Figure 11 : Wavy growth lines

Figure 12 : Flux residue

Figure 13 : Nail-shaped inclusion

From the above observations, it can be seen that group B is synthetic emerald.

Group D (Figure 14, Figure 15, Figure 16, Figure 17, Figure 18, etc.)

               Figure 14 : Parallel tubular inclusions

Figure 15 : Negative crystal, gas-liquid inclusion

Figure 16 : cavities

                                                                                          Figure 17 :  Solid inclusion (chromite)

Figure 18 : Black mineral inclusions and a large number of cracks

 Figure 19 : Fibrous inclusions

   Figure 20 : Three-phase inclusion

From the observed phenomena, it can be seen that group D is natural emerald.

Conclusion

Make a table to record the above test data