*Methods for gemstone identification

1. Refractometer?

Using a refractometer can measure the refractive index and birefringence of gemstones. In the process of gem detection, refractive index and birefringence are two very important optical constants and are the main basis for identifying gems. ?

2. Polarimeter?

The main purpose of the polarimeter is to judge the optical properties of gemstone materials based on the different phenomena of gemstones under the polarizer. In addition, adding a lens to the polarizer or configuring a glass interference sphere can be used to observe the interference pattern of anisotropic gemstones to determine the axiality of the gemstone. ?

3. Dichroic mirror?

Some colored gemstones will show different colors or shades of the same color when viewed from different directions under transmitted light. This pleochroic phenomenon in gemstones can be observed with a dichroic mirror. Pleochroism is also an important characteristic of colored heterogeneous gemstones. ?

4. Spectroscope?

Many gemstones are colored because they contain certain color-causing elements. These color-causing elements have their own absorption characteristics, which can be observed with a spectroscope. The absorption spectra of gemstones, especially for gemstones with typical absorption spectra, the results after spectroscopic testing can be used as an important basis for identification. ?

5. Color filter?

The characteristics of color filter are simple structure, compact instrument, easy to carry, and can observe multiple samples at the same time, and the identification is fast. The earliest and most commonly used Charles filter. Used to detect similar green and blue gemstones and identify their imitations. ?

6. Ultraviolet lamp?

There are two main types of luminescence in gemstones: fluorescence and phosphorescence. The difference in luminescence of different gemstones can also be used as an auxiliary detection method to identify gemstones. The fluorescence and phosphorescence characteristics of gemstones can be observed with ultraviolet light.

*Commonly used gem identification instruments

Gem identification can generally be divided into two categories: rough stones and finished products.

The identification of rough stones can be divided into field identification and indoor identification. Most field identifications use simple tools such as magnifying glasses and knives to initially name gemstones and minerals. Indoor identification mainly uses various means and instruments to further determine the data of gem minerals, providing an important basis for identifying gems.

For the identification of finished gemstones, the gemstones being measured must be identified without destroying the integrity of the gemstones.

The currently commonly used and easy-to-master gem identification instruments include the following:

1. Pen-type spotlight flashlight: used to observe the transparency of dense-colored gemstones. The electric beads of the spotlight flashlight should be concave on the surface of the pen tip and cannot protrude from the surface of the pen tip, otherwise it will be difficult to observe.

2. Magnifying glass: It is one of the instruments used to magnify and observe gems. The most commonly used magnifying glass is 10x, and there are also 20x and 30x magnifying glasses. A magnifying glass is a key tool and must-have for gemologists and is easy to carry. It can be used to identify the variety and authenticity of gemstones. Use a magnifying glass to observe: (1) Surface damage, scratches, and defects on gemstones. (2) Cutting quality. (3) Polishing quality. (4) Defects and inclusions within gemstones. (5) Color distribution and growth lines, etc. When identifying, the gem should be placed under strong light about 2.5 cm away from a 10x magnifying glass, and slowly adjust the distance until you can see it clearly. The quality of the magnifier you choose is also very important. Poor quality magnifiers will produce graphic distortion when magnifying.

3. Dichroic mirror: Some gemstones are pleochroic. The best instrument for observing the pleochroism of gemstones is a dichroic mirror. The dichroic mirror is an optical instrument with reasonable structure, cheap price, small size and simplicity. The dichroic mirror uses a suitable transparent colorless calcite (iceland stone) rhombohedron. Due to the high birefringence of iceland stone, the instrument can separate two plane-polarized light rays passing through the gemstone. It is required that a single crystal gemstone with color and transparency can detect pleochroism. Jade cannot detect pleochroism. Dichroic mirrors are mainly used to distinguish ruby ??from red spinel, red purple ivory; distinguish blue spinel from tiny blue tourmaline; distinguish sapphire from blue synthetic spinel, etc. When using a dichroic mirror to detect a gem, the gem must be rotated until the two most different colors appear on the window.

To determine the trichromatism of a gemstone, it must be carefully and repeatedly tested. When observing from three different directions, the appearance of three colors is the trichromatism. Note during testing: The distance between eyes, dichroic mirrors and gemstone samples should not exceed 2-5 mm.

4. Refractometer: The refractive index is an important optical constant for transparent gems and the main basis for identifying gem varieties. There are two main methods for measuring refractive index: one is the direct measurement method, using a refractometer; the other is the relative measurement method, using the liquid immersion method. Refractometers are manufactured based on the principle of total reflection of light. Currently commonly used refractometers are only suitable for gemstones with a refractive index in the range of 1.36-1.81. The refractive index (N) of gemstones is calculated as the ratio of the propagation speed of light in air (V1) to the propagation speed in gemstones (V2) is a constant, that is, N=V1/V2. A homogeneous gemstone in which light propagates at a constant propagation speed and has the same refractive index is called a single refractive index. Heterogeneous gemstones have two readings in the refractometer. The difference between the maximum and minimum refractive index values ??is called birefringence. The refractometer is one of the most commonly used instruments by gemologists. It is small and easy to use. He can not only test the refractive index of faceted gemstones, but also use the point measurement method to measure the refractive index of curved gemstones.

5. Charles Color Filter: Color filters are designed to take advantage of the characteristic of absorbing specific wavelengths of light. It is a gem identification instrument composed of two gelatin color filters that only allow deep red and yellow-green light to pass through. The color filter is small, lightweight, and easy to carry. It is particularly effective in identifying some dyed gemstones and artificial gemstones, and is very effective in identifying bright-colored jadeite. It can identify emeralds and other imitations, but to accurately determine it, other methods must be considered. Emeralds appear red or pink under a color filter, while other natural green gemstones similar to emeralds do not appear red when viewed under a color filter.

6. Gem microscope: an important instrument for magnifying observation of gems. It is capable of detecting external and internal features of gemstones that cannot be clearly confirmed or observed with a 10x magnifying glass. The gem microscope can observe the inclusions, cleavage, twin crystal patterns, growth lines, and color bands inside the gem; observe the grinding, polishing and accidental damage of the gem; and identify the two-layer and three-layer stones of the combined gemstones. The gem microscope has a reasonable structure, complete auxiliary equipment, and a large variable range of magnification, generally 10 to 70 times. Gem microscopes have two light sources. Generally, a bottom light is used to observe the internal defects of gems, such as inclusions, cracks, etc.; a reflector lamp is used to observe the surface features of gems, such as fractures, color bands, cleavage surfaces, etc. The gem microscope is a precision instrument and must be used strictly according to the operating rules.

7. Thermal conductivity meter: Thermal conductivity meter is designed and produced based on the good heat conductivity of diamond. Most gemstones do not have thermal conductivity or have very low thermal conductivity, so thermal conductivity meters are generally designed to distinguish diamonds from artificial imitation diamond products. They are special instruments for identifying diamonds and other imitation diamond products. The diamond thermal conductivity meter consists of a metal needle-shaped probe and a control box. When the tip of the probe touches the surface of the diamond, the temperature drops significantly, and the measurement result is displayed by a signal light on the instrument head or a beep. The thermal conductivity meter is more than ten centimeters long, easy to carry and extremely convenient to use.

8． Polarizer: It is a simple optical instrument made on the principle that plane polarized light intersects perpendicularly and light cannot pass through. The polarizer is composed of two polarizers with vertical vibration directions, a bracket and a bottom lighting. Used to detect the optical properties (homogeneous or heterogeneous) and pleochroism of gemstones. Turn on the polarizer with the illumination lamp turned on to observe the changes in light and dark of the gemstone sample. (1) If the sample is bright and has no change in light and dark, it may be a cryptocrystalline or microcrystalline aggregate, such as chalcedony, jade, etc. (2) If the sample is completely black and there is no change in light and dark, change the sample to an angle and continue to observe. If there is still no change in light and dark, the sample is homogeneous. Gems that are homogeneous include equiaxed crystal system and amorphous gemstones. (3) If the gemstone is rotated 360°, the gemstone sample undergoes four light and dark changes, which indicates that the sample is heterogeneous. Gems that are heterogeneous include gemstones in the tetragonal, hexagonal, trigonal, orthorhombic, monoclinic and triclinic crystal systems.

(4) If dark serpentine, grid-like or irregular phenomena can be seen when the sample is rotated under cross-polarized light, it may be an abnormal interference color presented by a homogeneous gemstone, and great attention should be paid to this situation. . Using polarizers, the pleochroism of gemstones can also be detected, and the heterogeneity and homogeneity of gemstones can be verified.

In addition, commonly used gem identification instruments include absorption spectrographs, fluorescent lamps, X-ray diffractometers, electron probes, etc.