Diamond is known as the "king of gems" and is recognized as the most precious gem in the world. Diamonds are hard, shiny, hard to wear, with large refractive index and strong dispersion, so they can emit charming "fire color". The country where diamonds were first discovered was India. At present, the most important diamond producing areas in the world are Africa, Australia, Russia and Canada, among which Africa is the most important. At present, the world diamond distribution is mainly controlled by De Beers United Mining Co., Ltd., which controls about 80% of the world diamond production through the central sales organization. De Beers mainly mines diamonds in South Africa, and through its diamond limited company and subsidiaries, it also controls diamonds outside Africa and other western countries. Diamonds can be divided into five-color to light yellow series and color series according to color. The five-color series includes nearly colorless and yellowish, brown and light gray. The color series includes yellow, brown, red, pink, blue, green and purple. In addition, there are black diamonds with a lot of graphite inclusions, and most of them in colored diamond are dark in color. Among them, Blue Diamond and pink diamond are the best. Because it is extremely rare, it is extremely expensive. The world-famous "Cullinan", "Noble" and "Hope" are all light blue diamonds. As the saying goes, "Gold is valuable, but diamonds are priceless", and diamonds are regarded as priceless. But in fact, the value of a diamond can be determined by its "4C", that is, its quality (carat), color, carat-ity and cut. Among them, the quality of diamond is the most important factor affecting the value of diamond. Diamonds of the same quality, the greater the quality, the more precious. Generally speaking, the quality of diamonds is only calculated in the last two decimal places of carats (1 carat: 0.2g), and the opinions of the third decimal place are 8 to 9. However, the relationship between diamond value and quality is not a simple linear relationship, but a complex geometric relationship. The diamond value of 29 points and 30 points, 49 points and 50 points, 59 points and 60 points, 89 points and 90 points, 99 points and 1 carat is very different. The value of diamonds is also affected by clarity and color. The higher the clarity, the better the color gradation and the higher the value of the diamond. The whiter a diamond is, the rarer it is. Among the four elements of diamond evaluation, cutting is directly affected by human factors. At present, the common diamond cutting patterns on the market are round, heart-shaped, drop-shaped, square, oval, emerald and so on. The quality of cutting directly affects the fire color of diamonds. The more accurate and reasonable the cut, the more attractive the diamond will be. Identification of fake and inferior crystals Because diamonds are scarce and expensive, there are many imitation crystals on the market. These imitations are mainly five-color gemstones, such as colorless glass, five-color zircon, colorless crystal, colorless sapphire, colorless topaz, colorless spinel, artificial rutile, artificial strontium titanate, yttrium aluminum garnet, gadolinium gallium garnet, artificial cubic zirconia and artificial moissanite. At present, artificial cubic zirconia and artificial moissanite are the most ideal diamond imitations. The main distinguishing features of diamonds and their imitations are as follows: 1. Glossy diamonds have a unique diamond luster, which is one of the main characteristics that distinguish them from other imitations. 2. The characteristic diamond with fire color presents a special "fire color" because of its high refractive index and high dispersion value. The fire color of diamond is soft and dynamic, while the fire color of imitation diamond is dull and monotonous. 3. Perspective effect Put the diamond table face down on a piece of paper with lines. A perfectly cut diamond can't see the lines on the paper, otherwise it is an imitation. 4. Oil-loving natural diamonds have strong oil affinity, and a clear and continuous line can be left after being scratched on the diamond surface with an oily ink pen. On the contrary, when they scrape on the surface of the diamond imitation, the ink gathers into small oil droplets, and continuous lines cannot appear. 5. Hydrophobicity: Dropping water on the diamond surface can stay on the diamond surface for a long time. If it is an imitation, the water droplets will disperse quickly. 6. Good thermal conductivity Because the thermal conductivity of diamonds is very high, breathing on diamonds can find that the fog disappears quickly, while obvious fog can be seen on the surface of imitations, which will take some time to disperse. 7. The face is straight and sharp. Because diamond is the hardest substance in the world, the edge line between polished diamond facets is flat and sharp, and the imitation has low hardness, smoothness and wear resistance. At present, synthetic cubic zirconia and synthetic moissanite are most similar to diamonds. The synthesized cubic zirconia is white in color, high in purity, free of natural inclusions in diamonds, low in hardness, smooth in edge line, high in density and heavier in hand feel than diamonds. The color of synthesized moissanite is grayish green, the dispersion value is higher than that of diamond, the fire color is stronger than that of diamond, and there are a large number of white needle-like inclusions arranged in parallel. Because of its high birefringence, you can see the double image of polyhedron under the magnifying glass of 10 times. These characteristics can distinguish it from diamonds.