Diamonds are found in the ocean, supporting a specialized and technologically advanced offshore mining industry. A diamond is a crystalline form of pure carbon, known for being the hardest naturally occurring material on Earth. While they are not scattered randomly across the seafloor, commercially viable concentrations are found in specific marine environments. These seabed deposits are the final destination for diamonds that began their journey millions of years ago in the planet’s deep interior.
Formation and Terrestrial Sources
The origin of these carbon crystals begins over 150 kilometers deep within the Earth’s mantle, beneath ancient continental plates known as cratons. Extreme pressures and temperatures, often exceeding 900°C, provide the necessary conditions for carbon atoms to crystallize into diamonds. These deep-seated diamonds are then brought rapidly to the surface through rare, violent volcanic eruptions.
These eruptions form geological structures called kimberlite and lamproite pipes, which are the primary source rocks. The rapid ascent of the magma prevents the diamonds from reverting to graphite, preserving their structure. Erosion of these primary deposits releases the diamonds, initiating the formation of secondary, or alluvial, deposits. The diamonds’ exceptional hardness allows them to survive this destructive process as they are moved and concentrated by natural forces.
How Diamonds Enter the Marine Environment
The primary mechanism transporting diamonds from land sources to the ocean is fluvial transport, carried out by powerful river systems. Rivers erode continental deposits, picking up the heavy, durable diamond crystals and carrying them downstream toward the coastlines.
The high specific gravity of a diamond, greater than most common sedimentary minerals, determines how they are deposited. As the river current slows upon reaching the ocean, it loses the energy required to carry the dense diamonds, causing them to settle out. This process, known as sorting, concentrates the heavier minerals in specific areas.
Coastal processes, such as wave action, currents, and longshore drift, further rework these river-mouth deposits. This constant agitation washes away lighter materials like quartz sand, leaving behind the denser diamond gravels. This action concentrates the diamonds into marine placer deposits along the continental shelf and submerged ancient river channels.
The most famous example occurs off the coast of Southern Africa, where the Orange River has transported diamonds from inland sources for millions of years. The river deposited massive quantities of diamond-bearing sediment into the Atlantic Ocean. The powerful Benguela Current then redistributed these sediments northward, creating one of the richest marine diamond fields in the world.
Current Status of Ocean Diamond Recovery
Commercial recovery of diamonds from the ocean floor is a specialized and technologically intensive operation, focused principally off the coasts of Namibia and South Africa. Namibia is a world leader in this field, with marine operations often exceeding 70% of the country’s total diamond production. This success is due to the highly concentrated and high-quality nature of the marine deposits.
The technology required to mine these deposits, typically found in depths ranging from 90 to 150 meters, is complex and expensive. Specialized marine vessels, essentially floating diamond mines, are deployed to the recovery areas. These ships are equipped with massive subsea crawler vehicles or large-diameter drill pipes that descend to the seabed.
The subsea crawler is a remotely operated machine that uses a suction system to excavate the diamond-bearing gravel from the seafloor. This material is then pumped up to the vessel for sorting and recovery. A notable example of this specialized fleet is the Benguela Gem, one of the world’s largest and most advanced diamond recovery vessels.
The diamonds recovered from the marine environment are frequently of exceptional quality, often yielding over 98% gem-quality stones in some deposits. This high proportion of valuable gems results from the ocean’s natural sorting mechanism, which eliminates weaker and more flawed crystals during transport. Commercial viability is strictly limited to these highly concentrated, naturally sorted marine placer deposits.