As a precious gemstone, diamonds have been highly sought after since ancient times, whether they shine in jewelry or play an important role in industry, diamonds always show their unique charm and value. So, how exactly is a diamond formed? Where can we find diamonds? This article will unravel these mysteries for you.
First of all, diamond and graphite may look completely different, but they are actually made up of carbon atoms. Graphite is formed by the layered arrangement of carbon atoms, which has the characteristics of low hardness and high temperature resistance; Diamonds, on the other hand, are tightly packed with carbon atoms and connected by strong covalent bonds, making them the hardest gemstones in nature.
Crystal structure of graphite (top) and crystal structure of diamond (bottom) Image credit: physics-in-a-nutshell.com
Scientists have discovered that the carbon in diamonds comes from the Earth's mantle. Under specific conditions of high temperature and pressure, carbon atoms in the earth's mantle form diamonds. Most diamonds are found in kimberlite, which is typically grayish-green in color and has a complex mineral composition.
Kimberlite (top) and diamonds in kimberlite (bottom) Image credit: geologyscience.com
Depending on the inclusions, diamonds can be divided into peridotite type and dolerite type, which are formed in the mantle at a depth of 120~180 km or more, respectively. Not only that, but Western Australia's potash-magnesium porphyry is also rich in diamonds. This rock is rich in potassium and magnesium, and characteristic minerals include feldspar and leucotite.
Potash Porphyry Image source: mindat.org
Diamonds can also be found in meteorites, basalts, ophiolites, and andesites. In addition, diamonds in alluvial placers are formed by weathering and sedimentation of diamond-bearing rocks. These places have the potential to be good places for your "treasure hunt".
Guinea mine placers mine alluvial diamonds, miners clean gravel Image credit: United States Geological Survey
Globally, there are several major diamond sources worth mentioning:
Africa:
Africa is one of the world's most famous diamond sources. South Africa, Botswana, Namibia, Angola and the Democratic Republic of the Congo are all well-known diamond producers. In particular, the Kimberley Mine in South Africa is known for its long history and abundant production.
Russia:
The Yakutia region of Russia is also an important diamond-producing region, with the Mirny Mine and the Yubileyny Mine both known as large, open-pit diamond mines around the world.
Canada:
Canada has been an emerging diamond source in recent decades, most notably the Ekati Mine and Diavik Mine in the Northwest Territories.
Australia:
Australia's Argyle Mine, known for producing pink diamonds, closed in 2020 but its impact on the diamond market remains profound.
Rough diamonds from Africa Image credit: NBCNEWS
Pink diamonds from Argyle Minerals Image credit: Grahams
Where can you "pick up" diamonds in China?
(Of course, you can't mine without permission.)
Since 1953, China has discovered multiple diamond deposits in Hunan, Shandong, Liaoning and other provinces, with proven reserves of more than 25 million carats. At present, China mines about 15 to 200,000 carats of diamonds every year, accounting for 0.5% of the world's total mining volume, of which gem-quality diamonds account for about 20%. It is known that kimberlite is distributed in Liaoning, Shandong, Guizhou, Hubei, Henan, Hebei, Shanxi, Jilin and other places, but the primary diamond deposits with industrial value are mainly concentrated in Liaoning and Shandong.
Diamonds from primary deposits are weathered, eroded, transported, and redeposited in a new environment to form diamond placers, where diamond grains are scattered but easier to mine. Diamond primary mines are widely distributed in the world, but the diamonds produced are extremely limited, accounting for about 1/4 of the total diamond production, and diamond placer mines account for 3/4 of the diamond production, and there is a large amount of gem-quality diamond production. China's most famous diamond placer mine is in the Yuanjiang River basin in Hunan.
Distribution of China's main diamond production areas The map of China comes from: the website of the Ministry of Natural Resources
1. Liaoning Wafang store
Wafangdian in Liaoning Province is the largest diamond mine in Asia and one of the major diamond-producing areas in China. The total amount of diamonds in the Wafangdian area of Liaoning Province is estimated to be 13.2 million carats, with high quality and large output. The diamonds here are characterized by colorless transparency and high clarity, with about 60% gem-quality diamonds selling for an average of $175 per carat, with the largest diamond ever found weighing 65 carats. The formation of kimberlite is associated with large faults in the deep mantle. The diamond deposits in the Wafangdian area are mainly distributed in the northern part of the Liaodong Peninsula, on the east side of the Tanlu fault zone. The kimberlite here exhibit features associated with deep fault zones, forming in a deep tectonic setting between the North China Platform and the Yangtze Platform.
Liaoning Wafangdian Diamond (top) and Wafangdian Mine (bottom) Image source: Pinterest (top) and National Geographic (bottom)
2. Mengyin, Shandong
Mengyin, Shandong Province is also an important diamond producing area, it is a large diamond source in the mainland, and many very large diamonds have been found. In 1937, the largest diamond in Chinese history, the "Golden Rooster Diamond", weighing 281.25 carats, was discovered in Jinjiling, Shandong, and was later looted by the Japan, and its whereabouts are still unknown. In 1977, the largest existing diamond in mainland China - "Changlin Diamond" was discovered in Changlin Village, Linshu County, Shandong Province, weighing 158.786 carats and pale yellow. In addition, there are 3 large diamonds with a quality of more than 100 carats, named "Chenbu No. 1", "Mengshan No. 1" and "Mengshan No. 5", weighing 124.27 carats, 119.29 carats and 101.47 carats.
The discovery of the Changlin diamond
On a winter day in 1977, Wei Zhenfang, a farmer from the Changlin Brigade in Mengyin County, Shandong Province, was working in the fields as usual. The hoe suddenly touched a hard object, and Wei Zhenfang looked down and found a shiny stone. Wei Zhenfang excitedly brought the stone back to the village, and the villagers gathered around to take a look. Speculation is that this could be a gem. The news quickly reached the local geological department. The experts arrived, and after careful examination, they were pleasantly surprised to find that it was actually a diamond weighing 158.786 carats! The diamond was named "Jobayashi Diamond" because it was found in the Jobayashi Brigade. Changlin diamonds are clean, transparent, pale yellow in color, and have a perfect octahedral shape. This discovery not only made the Changlin Brigade famous, but also let everyone know that Shandong Mengyin contains such precious resources. Today, the Changlin diamonds are properly stored in the vaults of the National Bank as an important treasure of the country.
Changlin Diamond picture source: Internet
The diamonds here are larger, but yellowish in color, mostly light brown and brown, with more internal inclusions, mainly for industrial use, and not many reach the gem grade, accounting for about 15%. The Mengyin area is located in the secondary fault on the west side of the Tanlu fault zone, and is also related to the large fracture of kimberlite and deep mantle in this area, which was formed in the North China Platform. The geological structure of Mengyin is complex, and the kimberlite contains a variety of mantle and crustal traps, indicating the trapping effect of magma on the surrounding rocks during the upswing.
Shandong Mengyin Diamond Image source: Pinterest
3. Yuanjiang, Hunan
Diamond placer deposits are mainly distributed on the terraces of the middle and lower reaches of the Yuanjiang River Basin. The enrichment law of diamond placer in three-dimensional space is as follows: (1) the lower the longitudinal direction, the higher the diamond grade and the better the quality; (2) Horizontally, the middle grade of the valley is higher, and it gradually becomes poor on both sides; (3) The main stream is of high grade and large diamond particles, and the diamond placer in the tributaries is of low grade and small particles; (4) Diamonds are often enriched in the lower part of slope and alluvium.
The diamond placer mine in Yuanshui, Hunan Province, produces better quality diamonds, and about 80% of gem-quality diamonds. Hunan diamonds generally have a strong diamond luster, dazzling brilliance; High crystal integrity. According to statistics, about 38.7% of Hunan diamonds have a quality of 0.1~0.25 carats, 19.8% are more than 0.25 carats, and the rest are 0.025~0.1 carats. Hunan diamonds are colorless and pure, accounting for about 4.5%; The surface is light yellow and light brown, accounting for about 68%; The surface has light yellow, light brown and other colors, accounting for about 17%, and yellow diamonds accounting for about 10.5%. The clarity is mostly VVS and VS, with gem-quality diamonds accounting for more than 60% and selling for an average of $130 per carat.
Diamonds in alluvial placer minerals Image credit: GoogleImage
The Yuanjiang River Basin is located on the southwestern edge of the Yangtze Platform and is part of the metallogenic belt in the middle and lower reaches of the Yangtze River. The diamond placers here are mainly derived from upstream kimberlite and other diamond-rich igneous rocks, formed through long-term weathering, transport and sedimentation. Diamond-rich sediments from rivers and alluvial fans in the region are particularly high in placer deposits, especially at the confluence of paleochannels and current channels.
Diamond clarity grade, the closer to the IF end the cleaner the inside Image source: AGS
In addition, kimberlite and potash-magnesium porphyry deposits have also been found in Guizhou, Henan, Hubei, Ningxia, Shanxi and other places. Despite the abundance of diamonds in these regions, the production of gem-quality diamonds is relatively low, making it difficult to fully meet the needs of the domestic market.
So, if you want to pick up diamonds in China, Wafangdian in Liaoning, Mengyin in Shandong, and the Yuanjiang River basin in Hunan are key locations. Wafangdian is known for its high-quality colorless diamonds, Mengyin is known for its large-grain industrial diamonds, and the Yuanjiang River basin is known for its high-quality placer diamonds. Despite its abundance of diamonds, China still faces challenges in quality and supply. In the future, with the advancement of exploration technology and the increase of development efforts, China's diamond resources are expected to be better utilized and improved.
Editor: Han Yatong
Proofreading: Li Yuchao
Source: Institute of Geology and Geosciences, Chinese Academy of Sciences
Editor: ArtistET
The reprinted content represents the author's views only
It does not represent the position of the Institute of Physics of the Chinese Academy of Sciences
If you need to reprint, please contact the original official account
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