The KZN diamond rush – and how we knew they weren’t real diamonds

In mid-June 2021, news broke of the discovery of a new diamond deposit in KZN (Kwa-Zulu Natal), South Africa, causing a massive diamond rush. South Africa has a long and famous diamond history, dating back over 150 years. The world’s biggest diamond ever was discovered here in 1905 so, in theory, a diamond discovery and subsequent rush didn’t seem too far-fetched.

In theory.

The beauty of theory is never a match for the mess of reality, however. And, when you looked at the situation objectively, the chance of a diamond deposit actually occurring in KZN, in that particular area – KwaHlathi, near Ladismith – there was really no chance at all of them being diamonds.

I’m a geologist by trade, having graduated from UCT with a Master’s degree before going on to work at De Beers (in their diamond exploration and research division) for many years prior to starting Katannuta Diamonds. It’s safe to say that I thus have a pretty good idea of where diamonds occur, why they occur in those areas and what they look like.

For myself and my fellow geologists, it was a little confusing as to why the government was taking so long to send scientists to assess the site and the “diamonds” when we could almost immediately conclude that they weren’t diamonds. But what made us so sure? How could we tell?

It boiled down to two key factors: geology and gemstone crystallography. We don’t want to overwhelm you with too much complicated science, but we hopefully want to explain it simply enough so that it makes sense.

1. Geology

Decade upon decade of research into where diamonds occur can be boiled down to a few basic principles. Firstly, diamonds occur in either primary deposits or secondary deposits. Primary diamond deposits are always a type of volcanic rock known as kimberlite (named, of course, after the city of Kimberley in South Africa) and primary deposits are the original source of all known diamonds. The only exception to this is a diamond mine in Australia called Argyle, which is a volcanic rock known as lamproite – a close cousin to kimberlite.

 

Secondary diamond deposits are found where diamonds have been eroded out of the primary host rock (kimberlite) and washed away into rivers, streams and, ultimately, the ocean. A great example of this are the diamond deposits on the west coast of South Africa and Namibia.

The second basic principle is that for a kimberlite to contain diamonds (because there are many known kimberlites, but not all of them contain diamonds), it has to be located on a craton (known as Clifford’s Rule, formulated in 1966).

What’s a craton, you might ask? A craton is one of the oldest parts of the earth’s crust, dated at 2.6 billion years or older and these cratons are scattered around the world, forming the building blocks of the modern day continents on which we live. In Southern Africa, a significant portion of South Africa, Botswana and Lesotho is made up of the Kaapvaal Craton, one of the oldest parts of the earth’s crust in existence.

 

 

Some of the world’s most important diamonds have come from kimberlite pipes located on this craton – the Kimberley diamond mines and Cullinan diamond mine in South Africa, Letseng diamond mine in Lesotho and the Karowe, Orapa and Jwaneng diamond mines in Botswana.

Now, how does all this relate to the location of the KZN diamond rush? The location of the so-called diamond deposit is off the Kaapvaal Craton. Not only is it off-craton, but there are no known kimberlites in the vicinity of this part of KZN. The geology is completely incorrect for diamonds to occur there based on simple geological principles.

 

2. Crystallography

The second significant red-flag for these so-called diamonds is the shape and crystal form of the gems that were being dug up and found. When diamonds grow in the earth’s mantle (over 150km below the surface), they can grow as one of only two crystal shapes – either cubic, or octahedral. From a crystallographic perspective, diamonds belong to the cubic crystal system. Due to the composition of diamonds (pure carbon) and the conditions under which diamonds grow, diamonds show very distinct crystal shapes.

An octahedral diamond shape is best described as looking like two pyramids placed base to base on each other. This is the most common primary shape of a diamond; cubic shapes are less common and when they do occur, these cubic shapes are generally not gem quality.

A secondary diamond shape known as a dodecahedron shape is very common, and this is not a primary growth form of diamonds. Instead, it derives from the octahedral shape over time. If an octahedral diamond is sitting in the mantle for an extended period, it starts to get resorbed, and the corners and edges get rounded off (think of an ice cube that starts to melt). With enough time, an angular octahedral diamond can become a significantly more rounded dodecahedral shape.

Each of these diamond shapes (octahedral, cubic and dodecahedral) are visually distinctive to the trained eye and the crystals being dug up in KZN bore no resemblance to known diamond shapes. Instead, photos of crystals from the dig site, posted to Twitter, showed shapes more commonly associated with quartz crystals.

Quartz belongs to the trigonal crystal system, and crystals are characterized by six-sided (hexagonal) prisms, often with a six-sided pyramid at one end (if the crystal has the pyramid shape at both ends, it’s known as a double terminated quartz crystal).

If you compare the shapes of diamond crystals with the shape of quartz crystals, you can see they are radically different. What do the KZN crystals most resemble? Quartz crystals, because that’s what they are. Have a look at the pictures below, of some of the gems that were picked up at the KwaHlathi site and you can see the typical quartz crystal shape in many of the examples.

 

 

So, there you have it – the two main reasons why the KZN diamond rush was going to end in disappointment for many people. Combining what we know about the geology of South Africa and diamond occurrences, with the crystal shapes of diamonds vs what was being dug out of the ground, had most geologists around South Africa agreeing that no, this was not going to be the next big diamond mine.

Of course, if you are looking for diamond experts, Katannuta Diamonds are the best people to speak to for a bespoke diamond engagement ring. With decades of experience in the diamond industry and an extensive knowledge of diamonds, gemstones and jewellery manufacture, we’re ideally positioned to help make your diamond dreams come true. Drop us a line via our contact page, or follow our Instagram and Facebook pages to see some of the magic jewellery we create.