Diamonds, the crystallized form of carbon, occur rarely in nature. Their creation is only possible in the extreme pressures found deep within the Earth’s mantle. It takes many years for diamonds to form underground and many more for them to reach the Earth’s surface. But strangely enough, diamonds can also be found at the site of a meteor impact. The conditions that forge diamonds over a vast period of time underground occur in a single instant when meteors collide with Earth.

Their rarity has made diamonds incredibly valuable. Today, diamond mining takes place in every continent with the exceptions of Europe and Antarctica. Over 25 countries host diamond mining operations, most run by large corporations that extract diamonds from primary deposits. But diamonds are also extracted by small-scale miners using simple, artisanal mining methods in secondary alluvial deposits. The following is a brief description of the common diamond mining methods used today.

Open Pit Mining

Also called “open-cast mining” or “strip mining”, open pit mining is a method of extracting precious rocks and minerals near the surface of the earth by their removal from an open pit or burrow. This mining technique is used when the diamonds are imbedded in a structurally unstable kind of earth, like sand or gravel, which makes it dangerous or impossible to use tunneling methods. Oftentimes, pit lakes tend to form at the bottom of open-pit mining sites due to groundwater intrusion.

Because open pit mining requires large amounts of land displacement, it is often a source of controversy. Many environmentalist groups object to large open pit mining due to the permanent damage it can cause to surrounding ecosystems.

Hard-Rock Mining

Hard-rock mining encompasses different mining techniques that all involve tunneling underground. A hard-rock mine involves drilling vertical tunnels, or shafts, deep into the earth to access precious stone deposits. Horizontal tunnels connect different underground “rooms” or “stopes”, which are supported by timber pillars. Horizontal excavations, called “adits”, can also be made into the side of a hill or a mountain to access deposits.

Now, high-tech machinery and new tunneling techniques have decreased the safety risks of hard-rock mining. But it is still one of the most dangerous types of mining, and in the past the death rate of miners working in hard-rock mines was very high.

Placer Mining

Placer mining is the mining of alluvial, or secondary, deposits. Diamonds usually come from geologic rock formations called Kiberlites. Rivers and streams can sometimes erode these formations over time and deposit the diamonds into sediments further downstream from their original source. The excavation of diamonds from these secondary deposits is sometimes accomplished through hydraulic mining (which uses water pressure to extract the diamonds) or through the use of mechanized surface excavation equipment.

Artisanal diamond mining is also common in alluvial diamond deposits. It involves very simple techniques, such as digging and sifting through mud or sand in streams using shovels and sieves.

Marine Diamond Mining

Marine mining is a more recently developed mining technique. Due to the high cost of the technology involved, it did not become commercially practicable until the beginning of the 1990s. Marine mining employs vertical and horizontal drilling methods to access diamond deposits in the ocean floor. Expensive underwater mining vehicles that crawl along the seabed are also used to excavate minerals from the sea floor.