Diamonds are the result of pure carbon atoms crystallizing under immense pressure, typically exceeding 4.5 gigapascals, and temperatures above 900 degrees Celsius. These conditions exist only deep within the planet’s interior, contributing to the rarity of these crystals. Understanding where diamonds are concentrated requires looking at the specific geological processes that bring them from the deep Earth to accessible locations.
The Deep Earth Origins of Diamonds
Natural diamonds form in the Earth’s mantle, at depths ranging from 140 to 190 kilometers beneath the surface. This zone, known as the diamond stability field, provides the necessary high-pressure and high-temperature conditions. These conditions are typically found beneath cratons, the oldest and most stable sections of continental crust.
Diamonds remain locked in the mantle rock until they are rapidly transported upward during a specific type of volcanic eruption. The carrier rocks are primarily kimberlite and, less commonly, lamproite, which form narrow, carrot-shaped conduits called pipes. The magma must ascend rapidly to prevent the diamonds from converting back to graphite as pressure decreases. Cratons are a prerequisite for finding primary diamond deposits, as they host the deep-seated pipes that tap the diamond stability field.
Global Leaders in Diamond Production
The vast majority of the world’s diamonds originate from primary kimberlite and lamproite pipe operations, with a few countries dominating both volume and value. Russia, largely due to its Siberian fields in the Yakutia region, consistently leads global production by volume, mining approximately 37.3 million carats in recent years. Russian operations, such as the Aikhal and Udachny mines, are characterized by high-volume output from multiple large pipes.
Botswana is the second-largest producer by volume but often rivals Russia in total value, reflecting the higher average quality of its stones. Mines like Jwaneng and Orapa are massive open-pit operations located on the Kaapvaal Craton, yielding exceptionally high-value diamonds. Other significant pipe-based producers include Canada, Angola, and the Democratic Republic of Congo (DRC). Canada’s mines are in the remote northern territories, while the DRC historically provides large volumes of smaller, industrial-grade diamonds.
Alluvial and Secondary Diamond Deposits
Not all diamonds are mined directly from their original volcanic host rock, as erosion and transport create secondary deposits. Alluvial deposits form when kimberlite or lamproite pipes are weathered away, releasing the diamonds into the environment. Because diamonds are extremely hard and dense, they are transported by rivers and streams and concentrate in gravel beds and ancient river channels.
Historically, the earliest diamonds were found in these secondary deposits, such as the riverbeds of India and Brazil. Today, significant secondary deposits are found in West Africa, including Sierra Leone and Angola, often mined through artisanal operations. Coastal Namibia is a unique, high-value source where ancient river systems carried diamonds to the Atlantic Ocean. Diamonds from secondary sources tend to be of higher average quality because the transportation process naturally destroys weaker, flawed crystals.