[Chemical composition] The component may contain elements such as N, B, Si, Al, Na, Ba, Fe, Cr, Ti, Ca, Mg, and Mn. Among them, N and B are the most important, which is the basic basis of diamond classification. First, according to whether or not N is divided into two categories: First, the type containing N is type I, and type I is further divided into type Ia and type Ib according to the existence form of N. â… a type N content exceeds 0.1%, in the form of a sheet of fine, enhanced hardness, thermal conductivity, electrical conductivity of the diamond. 98% of natural diamond is type Ia. The content of N in type Ib is small, N replaces C in diamond with a single atom, and most of type Ib is found in synthetic diamond, which accounts for only about 1% of natural diamond. Second, it does not contain N or has a very small content (<0.001%), and is further classified into type IIa and type IIb depending on whether or not B is contained. Type IIa generally does not contain B. The content of type IIa in natural diamonds is small. Good thermal conductivity is characteristic of IIa diamond. Type IIb contains B impurity elements, which are often blue-blue and have semiconductor properties. Type IIb diamonds are also rare in nature. In addition, mixed diamonds may also be present, that is, the distribution of nitrogen in the same granular diamond is not uniform, and there are both type I regions and type II regions; or both type Ia regions and Ib regions.
[crystal structure] equiaxed crystal system; 
; a 0 = 0.356 nm; Z = 8.
In the crystal structure of diamond (Fig. Z-5), C is distributed at the top of the eight corners of the cubic unit cell and the center of the six faces. When the unit cell is equally divided into eight small cubes, four of the small cubes are interphase. The center is distributed with C (Fig. Z-5(a)). C in the diamond structure is covalently bonded to the other four C groups around it, with a bond angle of 109°28′16′′, forming a tetrahedral coordination (Fig. Z-5(b)). The diamond has a compact structure between the atoms. Linked by strong covalent bonds, these characteristics result in high hardness, high melting point, and non-conductivity. Since the density of the surface of the atom in the {111} direction is large, the spacing is also large, resulting in {111} medium Cleavage.
Figure Z-5 Crystal structure of diamond
(quoted from Pan Zhaoyu et al., 1993)
[Form] Most of the diamonds in the natural world are produced in a single crystal, which is usually round or granular (Fig. Z-6). Its simple shape is mainly octahedron {111}, rhombohedral dodecahedron {110} and their polymorphism. A few are octahedron {111}, rhombohedron {110} and cube {100}, tetrahedron {hk0} into a shape. Common crystals are rounded due to erosion, crystal planes are curved (Fig. Z-7), and eroded images appear. Different monomorphs have different etched images, such as triangles appearing on octahedral crystal planes, and quadrilateral erosion on cubic crystal planes. pit.
Figure Z-6 shows an octahedral crystal diamond single crystal
Figure Z-7 Crystal form of diamond
(quoted from Wang Genyuan, 1989)
At present, some diamonds have also been found to have tetrahedral crystal shapes (such as several tetrahedral diamonds have been found in Liaoning, China), which may lead to the symmetry of diamonds. 3m, which contradicts the symmetry of diamond, which is generally considered to be m3m. For this problem, there have been reports on it that it is a pseudo-tetrahedral crystal form caused by a twin crystal structure (A. Yacoot, M. Moore, 1993).
[Physical properties] colorless and transparent, often with different shades of yellow, also milky white, light green, sky blue, brown and black, etc.; typical diamond luster, broken grease luster. Parallel {111} cleavage medium. Hardness 10. The relative density is 3.50 to 3.52. Crisp. The refractive index N = 2.40 ~ 2.48, with strong dispersion. Pure diamond has good thermal conductivity, and its thermal conductivity is almost five times that of copper at room temperature.
[Under] Causes and occurrence diamond formed only in the high temperature and pressure, the product magma is currently produced in only see ultrabasic rocks Kimberlite (brecciated mica peridotite), potassium, magnesium and high-grade rocks lamprophyre In the eclogite.
When the diamond-containing rock is weathered, a diamond sand deposit can be formed.
The world's famous diamond producing areas are South Africa, Zaire, and the former Soviet Union Yakuti. China's Shandong, Liaoning, Guizhou and other places have successively discovered diamond deposits.
[Identification characteristics] Very high hardness, standard diamond gloss, crystal contour is often rounded.
[Main use] Diamond has high economic value. According to the use, it can be divided into gemstone diamond and industrial diamond. The former mainly uses its lustrous color and high hardness. After diamonds are manually honed into various polyhedrons, it becomes a "diamond". The diamond is still the most delicate and most precious gemstone. The price is better and the price is better. Expensive, such as high-quality diamonds larger than 1g can reach more than 5,000 US dollars / carat. The latter mainly uses its various characteristics, such as the use of high hardness of type I diamond to make instrument bearings, glass knives, and table-mounted drill bits; the use of IIb-type diamond to make solid microwaves and laser devices to dissipate heat sinks; using its excellent infrared wear Transparently manufactures infrared windows for satellite windows and high power lasers. Rectifiers, triodes, etc. are fabricated using their semiconductor properties. With the rapid development of science and technology, the use of diamond is more and more extensive.
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