Diamonds: Extraction

Volcanic pipes from the mantle and X-ray sorting

Natural diamonds form deep in the mantle and reach the surface in kimberlite pipes, or are eroded into river and marine gravels, as in Namibia and Angola. USGS says most ore bodies hold from under 1 to about 6 carats per ton. Ore is crushed, and diamonds are recovered by dense-media separation and X-ray sorting. Natural industrial stones are mostly a by-product of gem mining. Synthetic diamond, made in high-pressure presses or by chemical vapour deposition, supplies over 99% of industrial diamond and a fast-growing share of gems.

Natural diamonds come from two kinds of deposits. Primary kimberlite pipes are mined in large open pits and underground mines, which supply most of the world's carats. Secondary deposits are diamonds washed out of pipes into rivers and onto beaches; these are mined by dredges and ships or dug by hand. Mined rough is then sorted and sold to cutters, most of them in India. Separately, factories grow diamond from carbon in presses or by vapour deposition. Synthetic diamond supplies more than 99% of industrial diamond and a fast-growing share of jewellery stones.

Methods compared

How each method works

Large pits are dug into vertical kimberlite pipes; when pits get too deep, mines move underground with block caving or sublevel methods. Ore is crushed and passed through dense-media separation, then X-ray sorters recover diamonds. Most of the world's large mines (Jwaneng, Orapa, Udachny, Venetia, Gahcho Kue) are of this type.

Large, long-lived and controllable; many of the largest mines are past peak and some will close soon (USGS 2026).

Diamonds eroded from pipes concentrate in river gravels and on the sea floor. Off Namibia, ships with seabed crawlers pump gravels for on-board treatment. In Angola, the DRC and Sierra Leone, much alluvial output is dug by hand and sold through local buyers.

Alluvial stones are often high value per carat; artisanal supply is hard to trace and was the source of conflict diamonds.

High-pressure high-temperature presses crystallise graphite into diamond grit or single crystals in minutes to days. Chemical vapour deposition grows diamond layer by layer from methane plasma onto seed plates, mainly for gem stones and optics.

Cheap and controllable; for gems it erodes the scarcity premium of natural stones.

Rough is planned by 3D scanning, sawn or laser-cut, bruted to shape and polished facet by facet. Small stones are cut in large Surat workshops; larger stones are often finished in Mumbai, Antwerp, Ramat Gan or New York.

Labour skill and scale give India a cost lead; margins are thin and depend on bank credit and rough prices.

Who does it: global

Who does it: India

India mines almost no diamonds but processes about 9 in 10 of the world's stones, mainly in Surat. FY2025 cut and polished exports fell 16.8% to $13.3 billion and rough imports 24.3% to $10.8 billion (GJEPC via Reuters); ICRA expects about $12 billion in FY2026.