Diamonds are naturally occurring minerals composed of pure carbon atoms arranged in a crystal lattice structure. Their exceptional hardness and unique optical properties make them valuable for industrial applications and jewelry. Mapping the global distribution of these minerals reveals a direct link between their presence and specific, ancient geological conditions, concentrated in a handful of countries.
The Geological Formation of Diamond Deposits
Diamonds originate in the Earth’s mantle, at depths exceeding 150 kilometers, where temperatures range between 900 and 1,200 degrees Celsius and pressures are immense (4 to 7 gigapascals). These extreme conditions exist within the mantle “keels” that underlie the oldest, most stable sections of continental crust, known as cratons. Cratons have remained tectonically stable for billions of years, creating the necessary long-term conditions for diamond crystallization.
The diamonds are brought to the surface through rare, violent volcanic eruptions via narrow, carrot-shaped conduits called volcanic pipes. The two primary host rocks are kimberlite and, less commonly, lamproite. These magmas rapidly transport diamonds and other mantle material to the surface before the diamonds can transform into graphite.
Leading Global Sources of Primary Diamonds
The majority of the world’s diamonds are extracted directly from primary host rocks. Russia is consistently the largest global producer by volume, with major deposits located in the Siberian region of Yakutia (Sakha Republic). Key Russian mines, such as Udachny and Mirny, exploit kimberlite pipes within the ancient Siberian Craton.
Botswana is a major source and often leads the world in diamond value due to the high quality of its stones. Mines like Jwaneng and Orapa are situated on the Kaapvaal Craton in Southern Africa. Canada has also emerged as a significant producer, with operations in the remote Northwest Territories, including the Diavik and Ekati mines, which access diamonds from the Slave Craton.
Australia was historically a significant producer, largely due to the Argyle mine in Western Australia, a lamproite pipe that was the world’s largest producer by volume for a time. Although the Argyle mine ceased operations in 2020, it was famous for being the primary source of rare pink diamonds. South Africa, where kimberlite was first identified near Kimberley, continues to mine primary deposits like the Venetia and Cullinan mines.
Alluvial Diamond Deposits and Their Locations
A different type of deposit, known as alluvial, forms when diamonds are eroded from their original kimberlite or lamproite source. Rivers, glaciers, and ocean currents transport the liberated diamonds, concentrating them in riverbeds, deltas, and coastal gravels. These diamonds are often of higher average quality because the transport process naturally removes weaker crystals.
West Africa has numerous alluvial deposits, particularly in countries like Sierra Leone and Guinea, where diamonds are recovered from river sediments. The Democratic Republic of Congo is a major global producer by volume, with a large portion of its output coming from extensive alluvial deposits, largely mined through artisanal operations in the Kasai region.
In Southern Africa, the Orange and Vaal Rivers transported diamonds westward from the interior kimberlite pipes toward the Atlantic Ocean. This created rich coastal and marine deposits along the South African and Namibian coastlines. Brazil’s production continues to be dominated by secondary deposits, first discovered in the alluvial gravels of the Jequitinhonha River in Minas Gerais in the early 1700s.