The identification of gems can generally be divided into two categories: rough stones and finished products.
The identification of the original stone can be divided into field identification and indoor identification. In the field identification, most simple tools such as magnifying glass and knife are used to preliminarily name gem minerals. Indoor identification mainly uses various means and instruments to further determine the data of gem minerals, which provides an important basis for gem identification.
For the identification of finished gemstones, it is necessary to identify the tested gemstones without destroying the integrity of the gemstones.
At present, the commonly used and easy-to-master gem identification instruments are as follows:
1. Pen spotlight flashlight: used to observe the transparency of dark gemstones. Beads of spotlight flashlight should be concave in the writing surface, not protruding from the writing surface, otherwise it is not easy to observe.
2. Magnifier: It is one of the instruments for magnifying and observing gems. The most commonly used magnifying glass is 10 times, and there are several kinds of magnifying glasses with 20 or 30 times. Magnifier is a key tool and necessary thing for gemologists, and it is easy to carry. It can be used to identify the variety and authenticity of precious stones. With a magnifying glass, we can observe: (1) the surface damage, scratches and flaws of the gem. (2) Cutting quality. (3) Polishing quality. (4) Defects and inclusions in gems. (5) color distribution and growth line. During identification, the gem should be placed under strong light about 2.5 cm away from 10 times the magnifying glass, and the distance should be adjusted slowly until it is clear. It is also important to choose the quality of the magnifying glass. Poor quality amplification will produce graphic distortion.
3. Dichroic mirror: Some gems are multicolored, and the best instrument to observe the multicolor of gems is the dichroic mirror. Dichroic mirror is a kind of optical instrument with reasonable structure, low price, compact and simple. The dichroic mirror uses a suitable transparent colorless calcite (Iceland spar) diamond. Because Iceland spar has high birefringence, the instrument can separate two plane polarized light rays passing through the gem. It is required that single crystal gemstones with transparent colors can detect polychromatic colors, while jadeite cannot detect polychromatic colors. Dichroic mirror is mainly used to distinguish ruby from spinel and red-purple tooth black; Distinguish blue spinel from blue tourmaline; Distinguish sapphire from blue synthetic spinel. When detecting a gem with a dichroic mirror, you must keep turning the gem until the two colors with the biggest difference appear on the window. For the determination of trichromaticity of gemstones, we must carefully and repeatedly test. Seen from three different directions, three colors seem to be three colors. Note during testing: the distance between eyes, dichroic mirror and gem sample should not exceed 2-5mm.
4. Refractometer: Refractive index is an important optical constant of transparent gemstones and the main basis for identifying gemstones. There are two main methods to measure refractive index: one is direct measurement and the other is refractometer measurement; The other is relative measurement, which cannot be immersed in liquid. Refractometer is made according to the principle of total reflection of light. At present, the commonly used refractometer is only suitable for gems with refractive index of 1.36- 1.8 1. The calculation method of the refractive index (n) of gemstones is that the ratio of the propagation speed of light in air (V 1) to that in gemstones (V2) is a constant, that is, N=V 1 /V2. An isotropic gem in which light propagates with constant propagation speed and equal refractive index is called single refractive index. Anisotropic gemstones have two readings in the refractometer, and the difference between the maximum and minimum refractive index values is called birefringence. Refractometer is one of the most commonly used instruments for gemologists. It is small in size and convenient to use. He can not only measure the refractive index of faceted gemstones, but also measure the refractive index of globoidal gemstones through point measurement.
5. Charles color filter: The color filter is designed by using the specific wavelength of absorbed light. It consists of two gelatin filters that only let dark red and yellow-green light pass through, and it is a gem identification instrument. The color filter is small in size, light in weight, and easy to carry, which is particularly effective in identifying some dyed gems and artificial gem, and is very effective in identifying colored jadeite. It can distinguish emeralds from other imitations, and it must be comprehensively considered by other methods in order to judge accurately. Emerald appears red or pink under the color filter, while other natural green gems similar to emerald do not appear red under the color filter.
6. Gem microscope: an important tool for magnifying and observing gems. It can detect the external and internal features of gems, which can not be clearly confirmed or observed with a magnifying glass 10 times. Gem microscope can observe the inclusions, cleavage, twin lines, growth lines and color bands inside the gem; Observe the grinding, polishing degree and accidental damage of gems; Distinguish between two-layer stones and three-layer stones that assemble gems. Gem microscope has reasonable structure, complete auxiliary equipment and large variable magnification, which is generally 10 to 70 times. Gem microscope has two kinds of light sources. Generally, the bottom lamp is used to observe the internal defects of gems, such as inclusions and cracks. Observe the surface features of gems, such as cracks, bands and cleavage planes. , with reflective lights. Gem microscope is a precision instrument and should be used in strict accordance with the operating procedures.
7. Thermal conductivity meter: Thermal conductivity meter is designed and manufactured according to the good thermal conductivity of diamond. Most gems have no or very low thermal conductivity, so the general thermal conductivity meter is designed to distinguish diamonds from artificial imitation diamond products, and it is a special instrument to distinguish diamonds from other imitation diamond products. The diamond thermal conductivity meter consists of a metal probe and a control box. When the tip of the probe touches the diamond surface, the temperature drops obviously, and the measurement results are displayed by the chirp sound on the signal lamp or the instrument head. The thermal conductivity meter is more than ten centimeters long and easy to carry and use.
8. Polarizer: It is a simple optical instrument. Its principle is that plane polarized light intersects vertically and light cannot pass through. The polarizer consists of two polarizers with vertical vibration directions, a bracket and a bottom lamp. Used to detect the brightness (isotropic or anisotropic) and multicolor of gemstones. Turn on the polarizer of the lighting lamp and observe the light and shade changes of the gem sample. (1) If the sample is bright, it may be aphanitic or microcrystalline aggregate, such as chalcedony and jadeite. (2) If the sample is completely black and there is no change in light and shade, continue to observe from another angle; If there is still no change in light and shade, the sample belongs to isotropic body. Gems belonging to isotropic bodies are equiaxed and amorphous. (3) If the gem is rotated by 360, the brightness of the gem sample changes four times, indicating that the sample is not isotropic. Gems belonging to anisotropic bodies include tetragonal, hexagonal, triangular, rhombic, monoclinic and triclinic crystals. (4) If the sample rotates under orthogonal polarization, dark serpentine, grid or irregular shape can be seen, which may be the abnormal interference color of isotropic gemstones, so we should attach great importance to it at this time. Using polarizer, we can also detect the multicolor color of gemstones and verify the heterogeneity and homogeneity of gemstones.
In addition, commonly used gem identification instruments include absorption spectrometer, fluorescent lamp, X-ray diffractometer, electron probe and so on.
Several kinds of jewelry
Jade is divided into white jade, jasper, sapphire, jet, topaz, topaz, green jade, Beijing white jade and so on. Geographically, there are Xinjiang jade, Henan jade, xiuyan jade jade (also known as Xinshan jade), Australian jade, dushan jade jade, Southern jade and Canadian jade, among which Xinjiang Hetian jade is a famous specialty in China.
Agate-white, gray, red, blue, green, yellow, sheep liver, gallbladder, chicken blood and black agate. From the pattern, there are: rushes, algae, twisted silk, hawksbill agate and so on. Produced in northeast China, Inner Mongolia, Yunnan and Guangxi. And there is agate with water, called water bile agate.
Stones-turquoise, lapis lazuli, hibiscus stone, wood-changed stone (also known as tiger skin stone), peach stone (also known as golden powder jade), malachite, sapphire, sheep liver stone, tiger eye stone, Dongling stone, etc. Among them, turquoise is a famous product in Yunyang County, Hubei Province, China.
Crystal-crystal, amethyst, topaz, ink crystal, tea crystal (also known as smoke crystal), soft crystal, bristle crystal and hair crystal. It is produced all over China.
Emerald-there are purple, red, gray, yellow, white and other colors, but green is the most expensive. It is a famous specialty of our neighbor Myanmar.
Coral is a benthic coelenterate fossil, red and white, which is produced in Taiwan Province Province, China, with excellent quality.
Beads-pearls (seawater pearls and freshwater pearls) and cultured pearls (seawater pearls and freshwater pearls).
Treasures-diamonds, rubies, sapphires, emeralds, aquamarine, cat's eye gems, discolored gems, topaz gems, opals, tourmalines, pointed gems, garnet gems, zircon gems, olive emeralds, emeralds, quartz cat's eyes, feldspar gems, etc.