In addition, the high temperature and high pressure generated by the impact of aliens on the earth can also form diamonds. However, the diamond formed in this way is small in particle size and poor in quality, and cannot be used as a gem of jewelry.
When the earth's crust produces tension, solid rocks begin to move and break, and then earthquakes and volcanic eruptions occur. When volcanic lava rises from the deep part of the earth to the surface, it brings the diamonds formed in the deep part to the shallow part of the earth and the surface. After the lava cools, we can find diamonds in the cooled rocks. When diamonds are enriched to a certain scale, we call them primary diamond mines. Diamond-bearing rocks are weathered under natural conditions, and diamonds remain on hillsides, rivers and coasts and are enriched to form mineral deposits, which are called diamond secondary mines.
According to different mine types, different mining methods are adopted.
Open-pit mine: The diamond-bearing ore body is weathered, transported and enriched by river water and rainwater to form secondary ore. When mining, the surface eluvial soil should be removed, and the ore-bearing sand layer and rock cracks should be carefully cleaned. On average, 65,438+0 carats of diamonds can be selected from 200 tons of gravel.
Primary ore: drill a vertical shaft along the vein, then dig it horizontally to the vein, transport the ore to the surface, and break and separate the diamonds. At present, the mining depth of kimberlite mine in South Africa is 900 meters.
Placer: When diamonds are brought to the coast along the river, they are enriched on the beach to form ore. The mining method is to classify all the sand containing diamonds and select diamonds.
Seabed mining: the advanced offshore mining technology is adopted to separate ore-bearing ores on the seabed. De Beers Offshore Mining Company mines 4 million carats of diamonds in Namibia, which is 35,000m from the coast and the water depth is110m.
1905, a giant diamond weighing 3 106 carats was found in Primir Mine, South Africa, and it was named "Cullinan". In 19 1500 carats, another diamond weighing 1500 carats was found in this mine. According to its shape, color and repeated comparative study, it is determined that it should be the same as Cullinan. 1980 the third large diamond weighing 599 carats was found in this mining area. Primir mine in South Africa is recognized as the origin of giant diamonds in the world. Patty Jewelry tells you that the mineralogy of stone is called diamond. Diamonds are the hardest substance in nature. Gemstone diamonds are polished diamonds. Diamonds are crystals of carbon. Because carbon atoms are firmly connected in the crystal, they are extremely hard and nothing can be scraped. Diamonds are expensive because their refractive index is the highest in rock crystal and their dispersion is strong. When turning a diamond, it will reflect colorful brilliance and be extremely beautiful.
Among nearly 200 kinds of precious stones in the world, diamonds not only have unparalleled hardness and aesthetic feeling, but also dominate; But also the rarest in nature, because its forming conditions are very harsh. Things are rare and precious, and they are known as the "king of gems".
Hundreds of millions of years ago, hot magma in the deep crust (about 150-200 km) erupted upward along the ancient crater. Because the crater is often blocked, the rising magma is slowly cooled in the volcanic tube under great pressure (about 40 thousand to 60 thousand atmospheres). When the temperature drops to 1000- 1250. C, a small amount of pure carbon contained in it will crystallize into diamond. This kind of magmatic rock containing diamond was first discovered in Kimberly, so it is called Kimberlite.
Kimberlite was brought to the surface by crustal changes in a long geological age, and then weathered and destroyed into blue gravel. Because of its chemical stability and wear resistance, diamonds are invariably hidden in these blue gravels, that is, diamond placer is formed.
Diamond deposits are very scarce, and kimberlite is especially difficult to mine. For every 65,438+0 carats (equal to 0.2 grams) of diamond raw materials, an average of 4-5 tons of kimberlite or placer must be treated. In addition, in the process of rough cutting and honing of diamond, at least 20% will be lost. This shows how expensive diamonds are.