‘Mega-Diamond’ found in Botswana: what’s behind the monster gem boom?
An aerial view of the Karowe mine in Botswana. Image: Google Earth
A mega diamond with a staggering 1,174 carat value was recently restored from the Karowe mine in Botswana, making it one of the largest natural diamonds ever recovered.
More remarkable still, the stone was found alongside several other similar diamonds weighing 471, 218 and 159 carats – suggesting that the original diamond may have weighed over 2,000 carats when first formed.
The latest discovery follows another mega diamond of more than 1,000 carats recovered from the Jwaneng mine, also in Botswana, just a few weeks ago.
Why are we seeing a sudden rush in the recovery of these gigantic gems?
Are diamonds really “rare” as they say?
In 2020, world diamond production stood at 111 million carats that is to say a little more than 20 tons of diamonds. However, a small part of this production consists of high quality gemstones. The vast majority of diamonds are small, less than one carat.
Australia’s Argyle mine, famous for its pink diamonds (and once the world’s largest diamond mine by volume) has ceased operations at the end of last year because it was no longer economically viable. This is because most of the diamonds mined were small in size and therefore were only useful for industrial applications.
These little diamonds are so common that a diamond tipped scribing tool can be purchased for less than the price of a tank of gasoline.
Large gem-quality diamonds, on the other hand, are extremely rare. To understand why, we need to look at how diamonds are formed, as well as how they are mined.
How are natural diamonds formed?
Natural diamonds are billions of years old. They form deep within the Earth, where temperatures and pressures are high enough to crush carbon atoms into a dense crystal structure.
Some scientists have suggested there are vast quantities of diamonds hundreds of kilometers deep. But as the the deepest hole ever drilled is about 12 km, we will never be able to extract these diamonds from the depths.
We must therefore be satisfied with the relatively small fraction that rises to the surface. Diamonds near the surface of the ground are widely believed to have hitchhiked via a deep-spring volcanic eruption.
These violent events must be fast enough to bring the diamonds to the surface and at the same time the diamonds cannot be exposed to extreme heat, shock or oxygen. It’s a narrow Goldilocks storyline.
Most diamonds are found in igneous rocks called Kimberlite. Kimberlite “pipes” are carrot-shaped columns of rock, often a few tens of meters in diameter, at the top of deep-source volcanoes.
But only a small percentage of all known kimberlite deposits contain diamonds. And only a handful of them are rich enough in diamonds to warrant mining.
The ideal conditions are very hard to find. Only particular regions of a continent can harbor diamonds, as the crust must be thick enough to have hosted a deep volcanic event. It must also be stable and old – characteristics common in parts of Australia and Africa.
In addition, despite its reputation for being indestructible, diamond is a brittle material. This is a property that should be taken into account when polishing diamonds into gemstones. At regular atmospheric pressures, the diamond is not even the most stable arrangement of carbon atoms.
An overwhelming task
Large natural diamonds that manage to survive the tortuous path to the surface are often destroyed by the very process of their discovery. In most diamond mines, the ore is blasted with explosives and then crushed into fragments to search for diamonds.
But new technologies allow mines to process ore using X-ray ore sorting technology. This is specifically targeted for “mega diamond recovery”.
While the diamond world is notoriously secretive on the details, we do know that the last diamond in the Karowe mine was recovered using these new ones. technical. And it is likely that more of these mega stones will be discovered in the future.
Advances in diamond mining techniques, coupled with the inherent scarcity of mega diamonds, are a boon to Botswana, where diamonds constitute a significant portion of the country’s GDP.
Diamonds in the lab
Diamonds also grow in the laboratory. For decades, artificial diamonds have been made using high pressure equipment that mimics the extreme physical conditions deep in the earth.
Now, new technology using low pressure conditions and carefully controlled chemistry can make perfect diamond discs the size of a plate.
This chemical approach is used commercially to make gem quality stones for jewelry. But making diamonds this way takes patience. To grow a millimeter of diamond, you need the best part of a day, which means mining is likely to play a key role in the diamond industry for some time.
Jodie Bradby is Professor of Physics at the Australian National University. Nigel Marks is Associate Professor of Physics at Curtin University.
This article was originally published by The conversation and has been republished here under a Creative Commons license.