Where do diamonds come from? Depends on who you ask, really. On a recent trip to New York City’s Diamond District, “Belgium”, “Israel”, “all over” and “Africa” were actual answers from clerks at stores I visited. “Funny,” I thought. “I didn’t know that Belgium had diamond mines” (they don’t). Clerks I met had also unbelievably never heard of diamonds coming from Botswana (the world’s largest producer of diamonds by value) or Namibia (10% of global production by value, highest price per carat in 2013). To their defence, management, their supplier or even their supplier’s supplier may not know either. This is possibly a reflection of only a handful of consumers per year asking, but mostly because of upstream processes and realities — parcels of rough diamonds changing hands many times, new parcels created from mixing and matching rough diamonds from others to satisfy customer demand, and the process of sorting where rough diamonds are classified in to as many as 12,000 different categories without respect to origin at all.
There are two ways of answering the question “where do (rough) diamonds come from?”: by value and by weight. Unlike gold for example, one carat of diamond is not equal to another: differences in size, color, shape, and the inclusions/flaws in a given rough diamond determine what shapes a diamond can be cut and polished in to, or if they can be useful in jewelry at all (and therefore determine its value). By weight, the world’s largest sources of rough diamonds are Russia, Botswana, Congo, and Australia. But by value, the largest sources of rough diamonds are Botswana, Russia, Canada, Namibia, Angola and South Africa.
For those seeking a more scientific answer, diamonds are formed under conditions of extraordinary temperature (1300 degrees centigrade) and pressure (50,000 times normal atmospheric pressure) deep within the earth’s crust. Volcanic activity carries the diamonds in magma up towards the surface and the magma cools, leaving a diamond-containing, carrot-shaped pipe of bluish igneous rock called Kimberlite. Eventually that kimberlite pipe becomes eroded by wind and rain and the diamonds become visible at the surface (in what’s called an alluvial deposit), or remain embedded in the kimberlite rock below the surface (in what’s called a kimberlitic deposit), waiting to be discovered. While diamonds from alluvial deposits can be mined with equipment as simple as a shovel, pan and sieve (Artisanal Alluvial Diamond Mining, AADM), mining diamonds from kimberlitic deposits — the grand majority of world gem-quality rough diamond production — requires massive amounts of capital, geological and engineering mastery — the very opposite of the “muddy field” image possibly stuck in your head from Blood Diamond.
Interestingly, the geological difference between these two major types of diamond deposits has implications for their host countries, particularly the ability to regulate diamond production effectively or at all. Kimberlite mines (underground or open-pit) with their comparatively small geographic footprint, as are common in Botswana, Canada, South Africa and Russia, can be fenced and secured. In contrast, alluvial diamond deposits (as in Sierra Leone, the Democratic Republic of the Congo (DRC), Zimbabwe, Angola) can be scattered over hundreds of square miles, making them impossible to control access to, and also making them prime targets for illegal miners, smuggling, etc.
As extraordinary the natural circumstances through which diamonds are formed may be, the man-made journey from mine to “mine” is amazingly more complex, with elements of it “opaque even to other members of the diamond trade”, and best explained by Bain & Company’s excellent report, available here.