The chemical composition of diamond is C, which is a homogeneous polymorphic variant of carbon with graphite . In the mineral chemical composition, it always contains elements such as Si, Mg, Al, Ca, Mn, and Ni, and often contains impurity elements such as Na, B, Cu, Fe, Co, Cr, Ti, and N, and carbohydrates.
Mineral diamond crystal structure belongs to the same pole equiaxed bond tetrahedral configuration. The carbon atoms are located at the top and center of the tetrahedron and have a high degree of symmetry. The carbon atoms in the unit cell are connected by the same-pole bond at a distance of 1.54 î„™ (10-10 m). Common crystal forms include octahedron, rhombohedral dodecahedron, cube, tetrahedron and hexahedron.
The diamond has a Mohs hardness of 10 and a microhardness of 98 654.9 MPa (100 060 kg/mm 2 ). The absolute hardness is greater than 1 000 times that of quartz and 150 times greater than that of corundum . Mineral brittle, shell-like or staggered fracture, cracking along the crystal cleavage plane under small impact, medium or complete cleavage with parallel octahedron, incomplete cleavage of parallel dodecahedron. The mineral is pure and the density is generally 3 470~3 560kg/m 3 .
The color of diamond depends on the degree of purity, the type and content of the impurity elements contained in it, and it is extremely pure and colorless. Generally, it is yellow, brown, gray, green, blue, milky white and purple, etc.; pure is transparent and contains impurities. translucent or opaque; at cathode rays, X-rays and ultraviolet light, will emit different fluorescent green, sky blue, purple, green, yellow colors; cyan blue to dark chamber made of phosphorus after sunlight exposure light; adamantine luster, A small amount of grease or metallic luster, high refractive index, generally 2.40 ~ 2.48.
The thermal conductivity of diamond is generally 136.16w/(mâ€¢k), and the thermal conductivity of type IIa diamond is extremely high, 25 times that of copper at liquid nitrogen temperature, and drops sharply with increasing temperature, such as at room temperature. It is 5 times of copper; the specific heat capacity increases with temperature, such as 399.84J/(kgâ€¢k) at -106Â°C and 472.27J/(kgâ€¢k) at 107Â°C; the thermal expansion coefficient is extremely small, with temperature Increase and increase, such as 0 at -38.8 Â° C, 5.6 Ã— 10 -7 at 0 Â° C; 720 ~ 800 Â° C in pure oxygen, 850 ~ 1 000 Â° C in air, 2 000 under anaerobic Converted to graphite at ~3 000 Â°C.
Diamond is chemically stable, resistant to acid and alkali, and does not interact with concentrated HF, HCl, HNO 3 at high temperatures, only in the melt of Na 2 CO 3 , NaNO 3 , KNO 3 , or with K 2 Cr 2 O When the mixture of 7 and H 2 SO 4 is boiled together, the surface is slightly oxidized; it is corroded in a high-temperature gas of O, CO, CO 2 , H, Cl, H 2 O, CH 4 .
Diamond also has non-magnetic properties, poor electrical conductivity, lipophilic hydrophobicity, and triboelectricity. Only Type IIb diamond has good semiconductor properties.
According to the difference of nitrogen impurity content and thermal, electrical and optical properties of diamond, diamond can be divided into two types, I type and II type, and further subdivided into four subtypes of Ia, Ib, IIa and IIb. Type I diamonds, especially the Ia subtype, are common common diamonds, accounting for about 98% of the total natural diamond. Type I diamonds contain a certain amount of nitrogen, which has good thermal conductivity, poor electrical conductivity and good crystal form. Type II diamonds are extremely rare, with little or no nitrogen, good thermal conductivity and curved crystals. Type IIb subtype diamond is semiconducting. Due to its excellent performance, Type II diamonds are used in space technology and cutting-edge industries. The comparison of the two types of diamond characteristics is shown in the table below. [next]
Diamond ore has two types of magmatic rock and sand mine. Known diamond-containing magmatic rock Kimberley, magnesium, potassium and peridotite lamprophyre three kinds, and wherein the kimberlite type lamproite type of industrial interest. [next]
(i) Kimberly Rock
The kimberlite, the breccia mica peridotite, is the product of an independent high-temperature magma that is deeper than other magma sources in the continental plate. The kimberlite is an ultra-shallow, alkaline, ultrabasic rock with a breccia, massive structure, plaque structure or tuff-like structure, often containing some type of mineral, titanium minerals and deep-sourced Body, no feldspar . The rock mass is produced in the Precambrian ancient platform or the earth shield area, distributed in the secondary faults of the large fault structure, and is produced in the form of rock tubes, veins, rock walls or rock beds along the fault. Rock mainly composed of olivine, phlogopite, such as iron and magnesium mineral composition, typically containing several minerals characteristics, such as diamond, chromium, magnesium aluminum garnet, diopside chrome, chrome spinel, magnesium ilmenite, perovskite, the rare earth element content of anatase, rutile, and the like columbite, niobium, tantalum, and other more general ultrabasic rocks may be several times to several ten times higher. The rocks contain deep-source rocks and minerals such as olivine, pyroxene and diopside minerals, and olivine peridotite and oblique peridotite. According to the content of olivine and phlogopite, kimberlite can be divided into olivine-type kimberlite (olivine content >50%) and phlogopite-type kimberlite (mica content >50%).
At present, the world has found tens of thousands of kimberly rock masses, of which diamonds account for 20% to 30%, less than 5% of industrial value. In the industrial diamond-bearing kimberlite body, 90% of the rock tube (cylinder) is produced, such as South Africa, Botswana, Zaire, Australia and China.
(2) Potassium-magnesium lamprophyre Potassium-magnesium lamprophyre, also known as olive gold cloud volcanic rock, is a super-potassium and magnesium-rich ultrabasic volcanic rock. The rock mass is in the fracture activity zone at the edge of the platform, which is formed by rock tube, rock neck and rock wall. It has breccia and block structure. The breccia contains deep-sourced mites. The rock has a plaque or crystal structure. The main minerals are olivine, phlogopite, and orthopyroxene, diopside, chrome spinel, leucite , potassium-rich magnesium amphibole, andalusite , potassium-calcium plate zircon and Apatite, etc. In the chemical composition, K 2 O is 3% to 12%, MgO is 5% to 29%, and SiO 2 is about 40%.
According to the content of olivine and leucite, potassium-magnesium lamprophyre can be divided into olivine potassium-magnesium lamprophyre (olivine content greater than 20% to 50%) and leucite potassium-magnesium lamprophyre (leucite) The content is not less than 20% to 50%).
According to reports, although potassium-magnesium lamprophyre has been found in many parts of the world, there are not many diamond-bearing ore, and most of the industrial value is olivine-potassium-magnesium lamprophyre. At present, only the diamond deposits in the Argyll area of â€‹â€‹Western Australia are huge, and the Indian Magawan rock has industrial significance. Other diamonds in the potassium-magnesium lamprophyre distributed in the United States, Zambia, Ivory Coast, and Guizhou, China have no industry. value.
Several peridotite-type ultrabasic rocks have been discovered in Tibet, Xinjiang, and other places in China. They also contain diamonds and indicator minerals that are symbiotic with diamonds, such as magnesium garnet and perovskite. At present, the content has been found to be very small, the degree of geological research is shallow, and its prospecting significance and economic value need to be further explored. [next]
The ancient sand mines are widely distributed in the world, mainly in Ghana, Brazil, India, South Africa and other countries. The Quaternary coastal sand mines are widely distributed in the west coast of the Atlantic Ocean in southwestern Africa. The economically valuable sand deposits discovered in China are mainly The Quaternary river alluvial sand deposits distributed in the Lishui River Basin of Hunan Province, the Weihe River Basin of Shandong Province and the Fuzhou River Basin of Liaoning Province. The ore grade is low, the diamond particles are small, and there are often symbiotic gold, zircon and ilmenite. use.
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