Diamond Deposit Types

Diamond-bearing kimberlite pipes are scattered unevenly across the planet — the legacy of hundreds of millions of years of plate movement, as continents split, drifted and fused again into new landmasses. A handful of nations now supply the overwhelming share of the world’s rough: Russia, Botswana, South Africa, Angola, Namibia, Australia and the Democratic Republic of the Congo together account for roughly 80% of annual production.

Primary deposits

A primary deposit is a diamond found where it arrived — the kimberlite chimney itself, the original vehicle that raised the crystal from the depths to daylight. Mine a primary deposit and you are working the rock that the diamond travelled in, undisturbed since the eruption that placed it there.

Secondary deposits

Over millions of years, weather breaks kimberlite down. As the rock decomposes, the diamonds locked inside it are released and carried away by river, sea or wind — fluvial, aeolian and marine transport. Wherever they come to rest, they form a secondary deposit.

Here the diamond’s own density does the sorting. A diamond’s specific gravity of 3.52 makes it markedly heavier than the sand and gravel travelling alongside it, so it drops out of suspension and gathers wherever a current loses its pace. Stones recovered from these beds are known as alluvial diamonds.

Deposit	Where the diamond sits	Name
Primary	In the kimberlite pipe of its origin	Pipe diamond
Secondary	Moved by water, sea or wind from the pipe	Alluvial diamond
Tertiary, quaternary…	Re-transported again from a secondary bed	Alluvial diamond

A diamond need not stop at a single move. A secondary deposit can itself be eroded and the stones shifted onward into tertiary, quaternary and further beds — each step a fresh journey, sorting the heaviest, soundest crystals out as it goes.