In addition, diamond is one of the few transparent materials with the highest refractive index in the world. Therefore, diamonds have strong reflective ability and typical diamond luster. Moreover, the diamond is cut and polished according to the scientifically designed style, which can reflect all the light incident on the surface and inside, making the whole diamond shine. The dispersion of diamond is very large, that is, the refractive index of monochromatic light with different wavelengths is also very different. When white light enters the cut diamond, monochromatic light with different wavelengths in the white light will be separated, and the degree of separation will be greater when it passes through the diamond after many internal reflections. This dispersion phenomenon makes the diamond appear colorful flash, that is, fire color, which is extremely beautiful and charming. Diamonds are very scarce. Even in South Africa's diamond-rich mines, it takes an average of about 20 tons of ore to obtain 1 carat gem-grade diamonds. This explains why diamonds are so precious and attractive. Diamonds have the reputation of "the king of gems". Conspiracy, war, adventure stories and legends around diamonds are constantly circulating, which is unmatched by any other gem.
I. Basic nature
Crystallographic characteristics
Equiaxial crystal system.
Crystallization habits are often octahedron, rhombic dodecahedron, cube and so on. , and there are several simplex forms (Figure 6- 1).
Surface characteristics Because the diamond crystal develops complete octahedral cleavage in three directions, the surface has obvious cleavage lines, which becomes an important basis for identifying the original diamond.
Figure 6- 1 Geometry of Equiaxed Crystal System
(2) Chemical composition
Diamond is a simple mineral, the chemical molecular formula is C, and C atoms are connected by valence bonds, and their combination is very firm, so diamond has the characteristics of high hardness, high melting point, high insulation and enhanced stability. In addition to C, diamonds may also contain trace elements such as N and B, and according to this, diamonds are divided into two types, namely type I and type II.
Type I diamonds contain trace amounts of N. According to the existing forms of N, they can be further divided into type ia and type IB.
Type ia: n is centered on the atomic pair or N3, and the more, the yellower the diamond. In nature, most diamonds fall into this category.
Type IB: N appears as a single atom, which is rare in nature. The colors of this diamond are yellow, yellow-green and brown.
Type Ⅱ diamond contains no N, which is rare in nature because of its good thermal conductivity. According to whether it contains B or not and its conductivity, it can be further divided into Ⅱ A type and Ⅱ B type.
Type Ⅱ A: B-free, non-conductive, with the highest thermal conductivity, and the thermal conductivity at room temperature is 6.5 times that of copper.
Type Ⅱ B: Semiconductor transformed by a small amount of B, mostly blue in color.
Diamonds have high chemical stability. But when heated to 200℃ in CrSiO4, it can be converted into CO2, and when heated to 650 ~ 870℃ in oxidizing environment, it can also be converted into CO2.
(3) Physical characteristics
1. Optical characteristics
Colors vary greatly, often colorless, yellow, black, etc. ; A few are green, red, blue and other colors.
Gloss is a typical diamond luster.
Transparent, transparent and opaque.
The nature of light is isotropic, so it is completely extinction under the polarizer, but the crystal lattice of diamonds is often distorted by the structure, so some diamonds can be abnormally extinction under the polarizer.
The refractive index is 2.417 ~ 2.419; Unparalleled refraction.
The deviation is 0.044, which is relatively high. Therefore, diamonds have a high fire color.
Polychromaticity does not exist.
The intensity and color of luminescence vary greatly. Most colorless and yellow diamonds are blue and white, and about115 diamonds will fluoresce under ultraviolet irradiation. Green fluorescence is common in brown and green diamonds.
Absorption spectra Diamonds of different colors have different absorption spectra. Colorless yellow diamond has absorption lines at 478 nm, 465 nm, 45 1 nm, 435 nm, 402 nm, 423 nm, 4 16 nm and 390 nm. Blue-green diamonds have absorption lines at 537 nm, 504 nm and 498 nm.
2. Mechanical properties
Cleavage has three directions: complete octahedral cleavage. Therefore, the waist of polished diamond often has a V-shaped notch, which is one of the important characteristics that distinguish diamond from its imitation. It is this characteristic that is used to divide diamonds during processing (Figure 6-2).
Figure 6-2 Cleavage of Diamond
Hardness diamond is the hardest substance in nature, with Mohs hardness of 10 and scratch hardness of 140 times that of corundum. The hardness of diamond is anisotropic, and the hardness varies in different directions: octahedral direction > rhombic dodecahedron direction > cubic direction. In addition, the hardness of colorless transparent diamonds is slightly higher than that of colored diamonds. Cutting and polishing a diamond means polishing the soft direction of another diamond with the hard direction of one diamond. Only diamonds can be used to grind diamonds. Although diamond is the hardest substance in nature, its cleavage is developed and fragile, so hardness testing is generally prohibited in the identification of finished diamonds to avoid irreparable losses.
The density is 3.52g/cm3.
3. Other physical properties
Thermal expansion is very low, so the sudden change of temperature has little effect on diamonds. The diamond without cracks and inclusions is heated to 1800℃ in vacuum, and then cooled quickly, which will not bring any damage to the diamond. However, when heated in oxygen, the diamond will burn slowly and become CO2 gas only when it reaches a lower temperature (650℃). Laser drilling and cutting are based on this principle.
Thermal conductivity is the highest of all known substances. The thermal conductivity meter made of this property has become the fastest and most effective tool in diamond detection, and this property also makes diamonds used as heat sinks and temperature sensors in the electronic industry.
Except for a few rare natural blue diamonds (Ⅱ B type), their electrical properties are generally insulators. The purer the diamond, the more perfect its crystal lattice and the better its electrical insulation. If the diamond is irradiated by X-ray or γ-ray, its structure will be destroyed, and some free electrons will be produced, resulting in extremely small conductivity.
The surface of oleophilic diamond can't be wetted by water, but it has special oleophilicity. This characteristic is often used in diamond identification and mineral processing.
(4) Inclusion
Inclusions in diamonds include graphite, garnet, clinopyroxene, orthopyroxene, sulfide, olivine, kyanite, corundum, andalusite, calcite, mica, feldspar, amphibole, ilmenite, chrome diopside, chlorite, zircon and diopside. In addition, the growth line and cleavage of diamond can be seen by magnifying observation. Triangles, V-notches and beards related to cleavage are also common in rough stones and finished products.
Second, identify
Identification of diamonds is very important, because accurate identification of diamonds is necessarily the premise of diamond evaluation, trading, marketing and purchase. With the development of science and technology, more and more diamond imitations enter the market, such as Soviet diamonds (cubic zirconia), American diamonds (yttrium aluminum garnet), Swiss diamonds (strontium titanate), kyanite and so on. Many materials cut and ground in proportion will show the same or even higher brightness and fire color as diamonds, which can completely confuse fish with pearls. What's more, more and more synthetic diamonds and new methods of dealing with diamonds are constantly entering the market, and even professional jewelry appraisers are sometimes confused about their correct appraisal. Accurate identification of diamonds requires professionals to use various identification instruments. But generally speaking, the identification of diamonds needs to focus on the following issues: ① the identification of diamonds and imitations; ② Identification between natural diamonds and synthetic diamonds; ③ The difference between untreated diamonds and treated diamonds.
(a) Identification of diamonds and imitations
There are many imitations of diamonds in the market, such as yttrium aluminum garnet, gadolinium gallium garnet, zircon, cubic zirconia, strontium titanate, artificial rutile, artificial moissanite (Mosanite), glass and so on. But compared with other gems, it is relatively easy to distinguish diamonds from imitations (Table 6- 1). The most convenient way is to distinguish diamonds from other imitations by means of a thermal conductivity meter, because the thermal conductivity of all diamond imitations is much lower than that of diamonds except Mosan. On this basis, we should focus on the identification of Moshan stone.
Table 6- 1 Physical properties of diamonds and their imitations
sequential
Mousse stone is a kind of artificial gem produced and put on the market by American C3 Company in 1997, and its chemical composition is SiC. Compared with other diamond imitations, it is more deceptive because of its high thermal conductivity, which can not be distinguished from diamonds by traditional thermal conductivity instruments. In fact, it is not too difficult to identify this imitation. First, this material is anisotropic, with large birefringence, which can be distinguished with a magnifying glass of ten times. Secondly, it is easy to distinguish the two by using the reflectometer that has been put into the market.
(2) The difference between natural diamonds and synthetic diamonds.
Since the first artificial diamond came out more than 40 years ago, the technology of artificial diamond has been imperfect. Most synthetic diamonds are only used for industrial purposes, and few of them reach the gem level. Moreover, the cost of synthetic diamonds is more expensive than that of natural diamonds. Therefore, in the past, synthetic diamonds rarely entered the market, and people seemed to sit back and take it for granted that diamonds were natural. But in recent ten years, with the continuous improvement of synthesis technology, the cost has been reduced, the output has doubled, and the quality has been getting better and better. Almost colorless and clean people can be seen everywhere. Synthetic diamonds have begun to hit the market and need to be identified urgently. Based on the current research results, the identification of natural diamonds and synthetic diamonds can be comprehensively identified according to some obvious characteristics (Table 6-2).
Table 6-2 Differences between Natural Diamonds and Synthetic Diamonds
(3) Identification of natural diamonds and processed diamonds
Due to objective reasons, most natural diamonds have defects in one way or another, and some can't even be directly cut into finished products. Therefore, people have been trying to treat low-grade diamonds through a series of methods to improve their appearance, obviously improve their quality and maximize their value. The identification of processed diamonds has also become a very important aspect of diamond identification. Common diamond processing methods and finished product identification methods are as follows:
1. Laser processing
This method uses laser to eliminate obvious black spots and inclusions in diamonds, and the channels left by laser are filled with glass. White linear inclusions are an important basis in the identification of diamonds treated by this method.
2. Radiation and heating treatment
Some diamonds with bad color can be improved by radiation and heat treatment. Special knowledge and instruments are needed to correctly identify it. Residual radioactivity and special color patterns produced by radiation are the most important identification marks. For the blue diamond produced by radiation, non-conductivity is an important basis for identification.
3. Coloring treatment
Some yellowish diamonds can be painted blue on the waist or pavilion to make the yellow light. The identification method is to wipe with water or acetone before inspection.
4. Coating treatment
That is to say, plating a thin layer on the diamond by artificial diamond can increase the weight and improve the purity or color. The identification method is: amplification inspection or immersion inspection, which is easy to appear coating.
5. Splicing processing
There are three common cases of diamond splicing treatment: ① using synthetic colorless sapphire as crown and bonding strontium titanate pavilion. Take sapphire as the crown to ensure the hardness, and strontium titanate as the pavilion to improve the fire color. This kind of split stone can be identified by thermal conductivity meter. ② Take diamond as crown, and bond with other colorless and transparent materials. A thin layer of diamond in the crown ensures the luster and hardness of the assembled gem. It is difficult to determine the authenticity of this combination only by testing the crown, and it is necessary to test the pavilion to make a correct identification. ③ Two smaller diamonds are bonded to form a larger diamond. This kind of splicing can't be recognized by thermal conductivity meter, so it is necessary to observe the characteristics such as glue and bubbles in the splicing seam.
Third, the quality evaluation
The price of a diamond is closely related to its quality. They are all natural diamonds, and subtle differences in quality will cause great fluctuations in diamond prices. It can be said that diamonds are one of the commodities with the biggest price difference in daily life. In fact, in the current jewelry market, it is often not the authenticity of diamonds that causes disputes, but the vast majority are the differences in diamond quality. Because everyone wants to buy value-for-money diamonds, they hope to formulate a unified standard to grade the quality of diamonds. With the efforts of the international diamond industry, a relatively unified and recognized diamond quality evaluation standard has been formulated internationally. They are: carat weight, color, clarity and cut. Because the English letters of these four evaluation standards all start with "C", it is customary in the industry to call them "4C" standards.
(1) carat weight
1. Representation of weight
Carat metric carat is the most commonly used unit to express the weight of diamonds, usually abbreviated as carat. Traditionally, carat is abbreviated as "ct". In gemmology, 1ct = 0.2g = 200mg.
Point For diamonds smaller than 1ct, the weight is usually expressed in points, usually written as pt. Gemmology stipulates that1100 of 1ct is 1pt, which means 1ct = 100pt.
Grain) 25pt is called 1 grain. This unit is used to indicate the approximate weight of a diamond. For example, a 1/2ct diamond is about 2 grains.
How many diamonds per carat For small diamonds, the industry practice is not to say how many carats or cents they weigh, but how many diamonds per carat. For example, a bag of diamonds * * * has 50 diamonds of similar size, and the total weight is 1ct. When describing this batch of diamonds, we say "50 diamonds/carat" instead of 2pt each, because the weight of each small diamond cannot be exactly the same.
2. Diamond weighing
For diamonds that are not inlaid, their weight can be accurately weighed by a balance. However, there are many kinds of scales, and the accuracy of each balance is different. Therefore, we should pay great attention to the accuracy of the balance when using the sky. At present, the precision of the special electronic carat scale used in gem industry can reach 0.00 1ct, which can fully meet the requirements. It is difficult to accurately determine the weight of inlaid diamonds. The general practice is to make a preliminary estimate according to its size. The key is the cutting accuracy of diamonds. The higher the accuracy, the more accurate the weight estimation. Otherwise, there may be a big error. The commonly used calculation formula is as follows:
Weight of standard round drill = average diameter 2 × height 0.006 1.
Weight of elliptical drill = average diameter 2 × height 0.0062.
Weight of heart-shaped drill = length× width× height× 0.0059 (length: width)
Emerald diamond weight = length× width× height× 0.0080 (1.001.00).
×0.0092( 1.50︰ 1.00)
×0.0 100(2.00︰ 1.00)
×0.0 106(2.50︰ 1.00)
Weight of horse eye drill = length× width× height× 0.00565 (1.501.00).
×0.00580(2.00︰ 1.00)
×0.0585(2.50︰ 1.00)
×0.00595(3.00︰ 1.00)
Pear weight = length× width× height× 0.00615 (1.25:1.00)
×0.00600( 1.50︰ 1.00)
×0.00590( 1.66︰ 1.00)
×0.00575(2.00︰ 1.00)
The above-mentioned length, width and height can be measured with various measuring tools and gauges in millimeters (mm). The unit of weight of diamonds is carat (ct).
3. Carat weight and price
For the finished diamond, under the same other conditions (color, clarity and cut), the greater the weight, the higher the price. In the diamond industry, the price of diamonds is expressed by "price per carat". Usually abbreviated as P.C. For example, if the price is RMB 22,000 /ct and a diamond weighs 0.50ct, then its price is 0.50× 22,000 =11000 yuan.
Because the bigger nature is, the rarer diamonds are. At the same time, there is a general feeling in society that diamonds with 1ct, 2ct and 3ct are more noble than diamonds with integers slightly smaller than 1ct, 2ct and 3ct. These two factors are clearly reflected in the price quotation of each diamond. Therefore, the relationship between diamond price and carat weight in the market is not a simple linear relationship, but a line with steps at carat premium (Figure 6-3).
Figure 6-3 Schematic diagram of the relationship between diamond price and weight
Super steps also appear on the weights of 0.25 carats, 0.50 carats and 0.75 carats, and the larger ones appear on the whole carats of 1, 2 and 3.
(2) Color (color)
1. Grade characteristics of diamond color
Based on industry custom, diamonds can be divided into two series according to their colors. One is colored diamonds, such as red, blue, purple and brown. This series of diamonds is very rare in nature, so it also has high value, and the evaluation needs to be carried out separately. The other is a large number of colorless series. The colorless the diamonds in this series, the higher their value. However, because diamonds contain a small amount of impurities such as nitrogen, they are more or less yellow. In order to evaluate this series of diamonds, many grading systems have been put forward internationally. At present, the main diamond grading systems in the world are GIA and CIBJO. GIA's grading system is an English alphabet, starting with the best color D and ending with Z. CIBJO's grading system describes the grades of colors in simple terms. The traditional diamond grading system in China adopts the method of 100, that is, the best color is 100, and so on.
2. The practice of color grading
Generally speaking, the grading of diamond fineness requires the following four basic conditions, namely, a set of standard colorimetric stones, a suitable lamp source, a neutral grading environment and experience.
Standard Colorimetric Stone Every laboratory should have a set of ***7 colorimetric diamonds, which are called "main stones". Each diamond represents a standard "color", corresponding to the lower or upper limit of the color scale. By comparing the color of an unknown diamond with a certain colorimetric stone, the color grade of the diamond can be obtained. It should be noted that a color scale represents a color range, and many diamonds rated as the same color scale still have subtle differences in hue after careful observation.
When grading colors, a suitable light source needs a standard artificial light source without ultraviolet rays. The recommended light source for diamond color grading is 5000/5500K, which is generated at a temperature relative to absolute zero (-273℃).
Neutral grading environment grading environment will also affect the feeling of diamond color. Scattered light from non-standard ceiling lamps and sunlight from surrounding windows will make diamonds fluoresce. In addition, if the colors and tones of walls and ceilings are bright, it will also hinder eye observation and affect grading. It is required to have a neutral grading environment, and it is ideal to use standard light sources in darkrooms, or semi-darkrooms with neutral light colors on walls and ceilings.
Experienced diamond grading requires experienced diamond graders to master various grading standards and accurately grade diamonds.
3. Color grading step
Colorimetry is generally used for color grading, that is, the diamond to be evaluated is compared with the standard colorimetric sample stone to determine the color grading of the unknown sample to be compared.
4. Color and price
The color of a diamond has a great influence on its price. Other conditions (weight, clarity, cut) are the same, the higher the color grade, the higher the price. For example, the international quotation 1998, weight 1ct, clarity VS, and cutting are the same. The price of D-colored diamonds is about 15000 USD /ct, and the price of K-colored diamonds is about 5000 USD /ct, which is nearly three times different.
(3) clarity
1. Definition classification system
At present, the diamond clarity grading system popular all over the world is mainly based on the number of internal and external defects of diamonds. Diamond clarity classification has a unified name, logo and color in the world. External defects are uniformly marked with a green pen, mainly including redundant facets, original crystal planes, scars, small white spots, abrasion marks and abrasion marks. The characteristics of internal defects are uniformly marked with red pen, mainly including burrs, scratches, holes, notches, moire, feather cracks, crystal inclusions, internal growth lines and so on.
2. Necessary conditions for clear classification
Cleanliness Because diamonds are lipophilic, it is very important to remove all the grease and dirt on the diamond surface before testing, otherwise it will affect the evaluation results.
The definition is divided by magnification, and the correction magnifying glass with magnification of 10 is commonly used internationally;
Lighting requires as much light as possible to enter the diamond hall.
3. The steps of definition classification
First, check each facet one by one; Then determine the clarity. The main factors to be considered are as follows:
The number of inclusions The more inclusions, the lower the cleanliness.
Inclusions Size The larger the inclusions, the lower the brightness and clarity of the diamond.
The closer the inclusion position is to the middle, the greater the influence on clarity.
Inclusion brightness The darker the inclusion, the higher its clarity, so the lower its clarity level.
Other factors being the same, fuzzy clouds with similar size and location have less influence on definition than dark crystals.
(4) cut (cut)
In order to reflect the beauty of diamonds to the greatest extent, it is very important to process them accurately in an ideal proportion. Every part of a diamond needs a certain proportion. The evaluation indexes of cutting classification of round faceted diamonds are: table percentage, crown angle, pavilion depth percentage, waist thickness, sharp bottom size, decoration (referring to polishing degree and symmetry) and so on. Details are as follows:
It is estimated that the mesa width accounts for about 56% of the total waist diameter.
Crown Angle In ideal cutting, the crown angles of three kinds of cutting are generally between 33 and 34 30'.
Crown height accounts for about 14.4% of waist diameter. When evaluating cutting time, crown height is generally not evaluated separately, which is mainly controlled by table size and crown angle.
Waist Thickness The waist thickness of almost all round faceted diamonds is the thickest at 16 and the thinnest at 16, which depends on the symmetry of workmanship. The wavy band can be easily observed along the band line of the diamond.
The depth of the pavilion is generally about 43% of the waist diameter.
Diamonds with a bottom surface greater than 50 points require a small bottom surface. This kind of diamond has 58 faces. The bottom surface is only a small surface, which requires a positive position. If the bottom surface deviates from the center, it will cause some light leakage.
The cutting quality has a great influence on the price. American A.L.Matlins (1999) thinks that cutting has the greatest influence on diamond price in 4c, but diamond consumers in China often pay little attention to it. Therefore, some jewelers often sell diamonds with good color and cleanliness to consumers, which will bring losses to consumers, which should be highly valued.
Four. Genesis and source of the deposit
1. Genesis of the deposit
How are the mineral diamonds that make up diamonds formed? There is still controversy. Up to now, relevant hypotheses have been put forward, including: the origin of mantle-derived crystals, the origin of mantle-derived magma crystallization, the origin of meteorite impact, the origin of oil reservoir explosion, the origin of metamorphism and so on. The study of earth science combined with modern scientific experiments shows that the above hypothesis of diamond formation may be correct, but gem-grade diamond-diamond only occurs in kimberlite, lamprophyre and its secondary sandstone.
According to the study of inclusions, the diamond formation temperature is 900 ~ 1300℃ and the pressure is 4.5 ~ 6.0 GPA, which is equivalent to the depth of the earth 130 ~ 180 km. According to the age analysis of inclusions, the age of diamond formation is usually much earlier than that of kimberlite or lamprophyre that brought it to the surface, such as Kimberlite diamond mine in South Africa. Kimberlite was formed before 90 ~ 100 Ma, but the diamond in this mine was formed before 3300Ma. Diamond mines all over the world have the same characteristics. Therefore, it can be considered that diamonds were formed in the depths of the mantle in an ancient geological history. In the later volcanic activity, it was captured by kimberlite magma or K-Mg lamprophyre magma, brought to the surface, found in kimberlite and K-Mg lamprophyre, and formed diamond primary ore. After weathering and denudation of primary ore, diamonds are taken to rivers or coastal environments for deposition, forming secondary placer of diamonds. As of 187 1, all the diamonds in the world are found in secondary placer, which is still the main source of diamonds in the world. The first primary diamond mine was discovered in Kimberly, South Africa in 1870. Later, kimberlite or K-Mg lamprophyre primary diamond deposits were discovered in Botswana, Congo (DRC), Australia, Russian Federation, Brazil and China.
2. Country of origin
By the18th century, except a few diamonds were mined in Borneo, most of them were mined in India, including almost all the famous diamonds in history. 1725 Diamonds were discovered in Brazil on the South American continent. In the history of 100 years, Brazil's diamond output has always ranked first in the world, and this pattern was not broken by a large number of South African diamonds until the end of 19 (Zhou Zuyi et al., 200 1).
1866, the first "Eureka" diamond was found near Orange, South Africa, and thousands of people flocked here to look for diamonds. Going upstream, four years later, people finally reached Dutoitz next to Kimberly City. A kind of blue-green extrusive rock, named kimberlite, was found in the rock tube, which is the mother rock for diamond production. Today, thousands of kimberlite cones have been found in southern Africa, but most of them do not contain diamonds, or although diamonds are produced, they have no industrial value because of their low grade. The famous South African diamond mines include Kimberlite and Primir. Others, such as Congo (DRC), Botswana, Yakutia, Siberia, Mwadui, China and Wafangdian, Liaoning, are typical kimberlite-type diamond deposits.
1979, the K-Mg porphyry containing diamond, also known as ultra-K-Jinyun volcanic rock, was discovered in Australia, which is a new type of diamond production. This type is the late magmatic rock invading the early volcanic rock, which makes the intrusive rock and volcanic rock closely symbiotic. K-Mg lamprophyre belongs to iron, alkaline to alkaline basic-ultrabasic rocks. Lamprophyre pipes in Australia not only provide basic data for finding new diamond resources, but also are important producing areas of red diamonds. In order to avoid the danger of falling rocks, the mining of kimberlite cone diamonds has changed from open-pit mining to underground mining. A series of special separation technologies and equipment are used for diamond recovery, such as rotary crusher, mill, heavy medium separation, rotary elutriation tray, oil recovery, magnetic separation and X-ray separator. The diamond grade of each kimberlite cone is different. Generally speaking, 65,438+0 carats of diamonds are produced for every 2 tons of kimberlite containing diamonds. Some cones extract 0.2 carat diamond from each ton of ore, which is of mining value. Diamonds placer is the main source of diamonds in the world. The diamond reserves of placers around the world account for about 40% of the total diamond in the world, but account for about 60% of the total output. Diamond placers include coastal placers, river alluvial placers and residual placers, which are distributed in various geological and historical periods such as Cambrian, Late Paleozoic, Mesozoic and Cenozoic. The famous diamond-bearing conglomerate in Witwatersrand, South Africa, the residual placer in Primir, South Africa and Olapa, Botswana are all important diamond placers. Diamond placers with industrial value have also been found on both sides of Yuanjiang River Basin in Hunan Province. Besides the traditional sand washing method, the main methods and tools of diamond placer mining include ship recycling (dredger), dredger, river diversion and offshore mining.
At present, more than 20 countries in the world produce commercial diamonds, but the top five diamond producers are Australia, Democratic Republic of Congo, Botswana, Russia and South Africa. Other diamond producing countries are Angola, Brazil, China, C? te d 'Ivoire, Ghana, Guinea, Guyana, Indonesia, Libya, Lesotho, Namibia, Tanzania, Venezuela, Central Africa, Sierra Leone, India and the United States. China discovered kimberlite and diamond primary deposits in Guizhou and Shandong in 1965. 197 1 A primary diamond deposit was discovered in Wafangdian, Liaoning Province. At present, two primary diamond deposits still being mined are located in Wafangdian, Liaoning Province and Mengyin, central Shandong Province. Diamond placers are found in Yuanjiang river basin in Hunan, Tibet and Guangxi and Tancheng-Lujiang fault across Jiangsu and Anhui provinces.
Diamonds, known as the king of gems, occupy the highest share in the international jewelry market. In this task, the basic properties of diamonds (including crystallographic properties, chemical composition, physical properties and inclusion characteristics, etc.). ) Be sure to recite it. The key points of diamond identification need to master three aspects: first, the identification of diamonds and imitations; The second is the identification of natural diamonds and synthetic diamonds; The third is the identification of untreated diamonds and treated diamonds. The quality of diamonds mainly depends on 4C evaluation criteria and related methods. We must also have a full understanding of the relationship between diamonds, the origin and origin of diamonds.
Practice and thinking
1. What is a diamond? What's the relationship between diamonds and diamonds? Why is diamond called the king of gems?
2. What are the basic attributes of diamonds?
3. What is a type I diamond? What is a type II diamond? What is the basis of judgment?
4. Briefly explain why the hardness of diamond is the largest among natural substances, but its toughness is not the highest.
5. The thermal conductivity of diamond is the highest among natural substances. What is its specific use?
6. Briefly describe how to make full use of the complete cleavage characteristics of diamonds in three directions.
7. What is the 4C evaluation of diamonds? What exactly does it include?
8. What are the main problems in diamond identification?
9. What is the carat weight? How to weigh? What is the relationship between diamond weight and price?
10. How to roughly judge the color of a diamond? What are the conditions for diamond color grading?
1 1. What is the classification system of clarity? What is its applicability? What are the conditions for definition classification?
12. What are the main factors to consider in determining the clarity of diamonds?
13. What are the main indexes to evaluate the cutting quality of a very common round faceted diamond?
14. What are the main imitations of diamonds? How to identify them?
15. How to distinguish between processed diamonds and synthetic diamonds?
16. What are the conditions of diamond inlays? How to identify diamond inlaid stones?
17. What is Mosan stone? What is the impact on the diamond market?
18. Briefly describe the origin of diamonds and explain the main diamond producing areas in the world at present.