Roughly 49% of diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are mined from kimberlite and lamproite volcanic pipes, which can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface.

The conditions for diamond formation to happen in the lithospheric mantle occur at considerable depth corresponding to the aforementioned requirements of temperature and pressure. These depths are estimated to be in between 140-190 kilometers (90-120 miles) though occasionally diamonds have crystallized at depths of 300-400 km (180-250 miles) as well. The rate at which temperature changes with increasing depth into the Earth varies greatly in different parts of the Earth. In particular, under oceanic plates the temperature rises more quickly with depth, beyond the range required for diamond formation at the depth required. The correct combination of temperature and pressure is only found in the thick, ancient, and stable parts of continental plates where regions of lithosphere known as cratons exist.Long residence in the cratonic lithosphere allows diamond crystals to grow larger.

Diamonds can also form in other natural high-pressure events. Very small diamonds, known as microdiamonds or nanodiamonds, have been found in meteorite impact craters. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. Impact-type microdiamonds can be used as one indicator of ancient impact craters.

The magma in volcanic pipes is usually one of two characteristic types, which cool into igneous rock known as either kimberlite or lamproite. The magma itself does not contain diamond; instead, it acts as an elevator that carries deep-formed rocks (xenoliths), minerals (xenocrysts), and fluids upward. These rocks are characteristically rich in magnesium-bearing olivine, pyroxene, and amphibole minerals which are often altered to serpentine by heat and fluids during and after eruption. Certain indicator minerals typically occur within diamondiferous kimberlites and are used as mineralogic tracers by prospectors, who follow the indicator trail back to the volcanic pipe which may contain diamonds. These minerals are rich in chromium (Cr) or titanium (Ti), elements which impart bright colors to the minerals. The most common indicator minerals are chromian garnets (usually bright red Cr-pyrope, and occasionally green ugrandite-series garnets), eclogitic garnets, orange Ti-pyrope, red high-Cr spinels, dark chromite, bright green Cr-diopside, glassy green olivine, black picroilmenite, and magnetite. Kimberlite deposits are known as blue ground for the deeper serpentinized part of the deposits, or as yellow ground for the near surface smectite clay and carbonate weathered and oxidized portion.

Schematic diagram of a volcanic pipe

The Panna belt in Madhya Pradesh is the main diamond producing area. Recoverable reserves of about 1 Mcts have been estimated. An additional 265 000 carats have been classified as”submarginal reserves”. Here the National Mineral Development Corporation (NMDC) of India operates the country’s only diamond mine, Majhgawan in Panna. The Dharwar craton has been the target for India’s diamondfierous kimberlite potential.

De Beers, Rio Tinto, BHP Billiton (in joint venture with Dwyka diamonds), Oropa and Indian Resources are exploring for diamonds in several states of India. India is the largest processor of diamonds in the world. By volume, India accounts for over 90% of the global market share in diamond cutting and polishing but for nearer 60% by value.