Gemstone Spectroscope
Gemstone Spectroscope
The coloring elements in gemstones often have specific absorption spectra. By observing the absorption spectra of gemstones, it can help identify the variety of gemstones, infer the causes of gemstone coloring, and study the color composition of gemstones. We can use a gemstone spectroscope to observe the absorption spectrum of gemstones. Gemstone spectroscope are divided into two types: prism spectroscope and grating spectroscope.
Principle and structure
- Prism type spectroscope
The prism type spectroscope uses a triangular prism as the dispersion element, and its working principle is shown in Figure 1.
Working process: After passing through the gemstone, the white incident light will be partially absorbed by the gemstone, and the remaining light will enter the spectroscope through the slit. The incident light will then pass through the collimating lens and become a parallel beam. After parallel light passes through a prism group, the prism group refracts light of different wavelengths into different directions, forming spectra of different colors. Due to the different absorption of light by different gemstones, the displayed spectra will also be different.
Figure 1 Principle diagram of Prism type spectroscope
- Grating type spectroscope
The grating type spectroscope uses a grating instead of a prism as the dispersion element. A grating is a diffraction screen with periodic spatial structure or optical properties. When white light passes through the grating, diffraction occurs, forming a series of spectra. The working process is similar to prism style.
Figure 2 Principle diagram of grating type spectroscope
- Differences between grating type and prism type spectroscope
Prism type spectroscope: The blue purple region of the spectrum is relatively wide, while the red region is relatively narrow (Figure 3), and the resolution of the red region is worse than that of the blue region;
Grating type spectroscope: The spectral regions generated are roughly equal (Figure 3), and the resolution of the red region is higher than that of the prism type.
Figure 3 Comparison of spectra between prism and grating spectroscope
Operation steps
- Transmission method (Figure 4): Suitable for transparent or semi transparent gemstones.
- Place the gemstone above the light source to allow light to pass through the gemstone;
- Place the spectroscope above the gemstone, align the slit with the gemstone, and allow the light passing through the slit to enter the spectroscope;
- Keep your eyes close to the eyepiece and record the observed spectrum.
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| Figure 4 transmission method | Figure 5 Reflection method |
- Reflection method (Figure 5): suitable for gemstones with poor transparency or opacity
- Place the gemstone on a black background;
- Adjust the angle of the light source so that it shines approximately 45 ° on the gemstone;
- The slit of the spectroscope is aligned with the reflected light on the surface of the gemstone, and the angle of the spectroscope is about 45 °;
- Keep your eyes close to the eyepiece and record the observed spectrum.
Matters needing attention
1. White light source (continuous spectrum) can be used, such as incandescent lamps, flashlights, or specially made fiber optic lamps;
2. The clarity of absorption lines (bands) in the spectrum is influenced by the size, color depth, and transparency of the gemstone;
3. Try to let the light passing through the gemstone enter the spectroscope as much as possible;
4. The slit of the spectroscope should be kept clean. If there is dust, black horizontal lines will appear on the spectrum;
5. When identifying gemstones, they should be used in conjunction with other identification instruments.
Common problems and solutions
Problem 1: It is known that a certain gemstone has no absorption spectrum, but during observation, absorption lines were found in the yellow green region or other region;
Solution: ① Human blood has varying degrees of absorption spectra, and if this phenomenon occurs, it is advisable to avoid touching gemstones with your hands.
② Some eyeglass lenses can cause varying degrees of spectral absorption.
Problem 2: Horizontal black lines can be seen in the spectroscope;
Solution: There is dust in the slit of the spectroscope, and it should be treated with dust removal. If it still cannot be restored after dust removal, please contact the manufacturer for assistance;
Problem 3: When observing a gemstone for a long time, it is found that the absorption line of the gemstone is blurred or disappears;
Solution: If the gemstone is exposed to light for too long, it will cause the temperature of the gemstone to rise. The increase in gemstone temperature has an impact on the absorption spectrum of the gemstone. It is necessary to immediately stop shining light on the gemstone and wait for it to cool before continuing to observe.
Problem 4: It is known that a certain gemstone has a characteristic absorption spectrum, but it cannot be observed;
Solution: The content of impurity elements will affect the obviousness of the absorption spectrum. You can try to rotate the gemstone to increase the distance the light passes through the gemstone to solve this problem.
Absorption spectra of common gemstones
| Gemstone Name | Absorption spectrum |
| Ruby |  |
| Red Spinel |  |
| Alexandrite |  |
| Emerald |  |
| Sapphire |  |
| Enstatite |  |