Diamond is pure carbon crystallized into an exceptionally strong structure. The creation of this gemstone requires one of the most extreme environments on Earth. These conditions transform carbon atoms into the dense cubic lattice that gives the diamond its hardness and brilliance. The unique journey from the deep Earth to the surface spans billions of years and involves violent geological events.
Formation Conditions in the Deep Mantle
The birthplace of nearly all natural diamonds is deep within the Earth’s mantle, not in the crust where mining occurs. This formation happens at depths ranging from approximately 150 to 200 kilometers (90 to 125 miles) below the surface. This immense depth is the only place where the necessary pressure and temperature conditions exist to stabilize the diamond crystal structure.
The required pressure for carbon to crystallize as diamond typically ranges from 5 to 7 gigapascals (GPa). This is equivalent to 50,000 to 70,000 times the atmospheric pressure at sea level. Simultaneously, the temperature must be extremely high, generally between 900°C and 1,300°C. This narrow window of pressure and heat defines the diamond stability field, outside of which carbon exists as the softer form, graphite.
These conditions are sustained only within the oldest, most stable sections of continental crust, known as cratons. Cratons have deep, cold roots that extend far into the lithospheric mantle, providing the ancient environment for diamonds to form and be stored. The carbon source is not coal, but rather carbon-rich fluids or melts originating from primordial mantle material or subducted oceanic plates.
The Journey Through Volcanic Pipes
Although diamonds form deep in the mantle, they must be rapidly transported upward to reach the accessible crust, or they will revert back to graphite upon entering a lower-pressure environment. This ascent is facilitated by a rare type of violent, deep-source volcanic eruption that creates narrow, carrot-shaped geological structures. These structures are known as kimberlite and, less commonly, lamproite pipes, named after the host rocks that solidify within them.
These magmas originate deep within the mantle, traveling at exceptional speeds to prevent the diamonds from being destroyed. The eruptions are some of the most rapid and volatile volcanic events in Earth’s history, explosively drilling a path through the continental crust. This rapid ascent preserves the diamond’s structure, carrying the crystals within the magmatic rock.
Kimberlite is the most dominant rock type that contains diamonds, and these pipes are the primary geological targets for diamond exploration worldwide. The solidified kimberlite or lamproite rock within the pipe is a direct sample of the deep mantle and the host material from which the diamonds are eventually extracted. Finding an exposed pipe is the first step in establishing a primary diamond mine.
Major Global Extraction Sites
The geographical distribution of diamond mines is directly linked to the presence of ancient cratons, which host the necessary kimberlite and lamproite pipes. Today, a handful of countries dominate global production, with major operations concentrated in two distinct “diamond belts.”
The largest producers include Russia, primarily from the Siberian craton in the Sakha Republic. Southern Africa remains a powerhouse, with Botswana, South Africa, and Angola hosting some of the world’s most valuable mines. Canada’s Northwest Territories represents a major source from the North American craton.
Diamonds are recovered from two types of deposits: primary and secondary. Primary deposits are the kimberlite and lamproite pipes themselves, which are typically mined through large-scale open-pit or underground operations. Secondary deposits, also called alluvial deposits, form when diamonds are eroded from the host pipes and transported by rivers or coastal action, often accumulating in riverbeds or marine gravels.
The Difference Between Natural and Lab-Grown Diamonds
A distinction must be made between diamonds made in the Earth and those produced in specialized facilities. Lab-grown, or synthetic, diamonds are chemically and physically identical to natural diamonds, but their origin is a factory rather than the deep mantle. These synthetic stones are created using one of two primary industrial processes designed to replicate the natural formation environment.
High-Pressure/High-Temperature (HPHT) Method
The HPHT method places a carbon source and a tiny diamond seed crystal into a press, subjecting them to conditions very similar to those in the Earth’s mantle. This process involves pressures around 5.5 GPa and temperatures up to 1,500°C.
Chemical Vapor Deposition (CVD) Method
The second method, Chemical Vapor Deposition (CVD), utilizes a different approach, growing the diamond layer by layer in a vacuum chamber filled with carbon-rich gases. The CVD process operates at lower pressures and temperatures, typically between 700°C and 1,300°C, and relies on carbon atoms from the gas mixture depositing onto a seed crystal.
Both techniques produce genuine diamonds, differing only in their origin: a laboratory versus the Earth’s ancient, deep interior.