How rough diamonds are mined
A diamond mine moves tons of rock to find stones present at no more than parts per billion.
- stations
- 3
- thing downstream
- 1
The short version
Most diamonds are carried up from the mantle in kimberlite, a blue-green volcanic rock found in pipes that reach from 75 meters to 1.5 kilometers across. Mines dig out the pipe or the loose gravels weathered from it. The rock is crushed and sorted, with diamonds picked out by density and sometimes glow under X-rays.
-
Dig out the pipe
Kimberlite sits in narrow dikes and in vertical pipes on the oldest, most stable parts of continents. Miners dig it from open pits that deepen into shafts. Before the 20th century, most diamonds were found in river gravels instead.
-
Crush the kimberlite
Rock is broken down carefully to free the diamonds without cracking them. Weathered kimberlite, the yellow ground, is easy to break apart.
-
Sort out the stones
Diamonds are concentrated by density, since they are heavier than most of the waste rock. Between 25% and 35% of natural diamonds fluoresce under X-rays, a property that sorting machines can use to find them.
Worth repeating
- Most natural diamonds are between 1 billion and 3.5 billion years old.
- Most formed at depths of 150 to 250 kilometers in the Earth's mantle.
- Before the 20th century, most diamonds were found in alluvial deposits, not mines.
- The only major diamond discoveries since about 1980 have been in Canada.
Where it goes next
Rough diamond feeds 1 line directly.
Keep walking
Sources
Cite this page: "How rough diamonds are mined." Assembly Line, 2026-11-03. https://assemblyline.org/make/rough-diamond