A diamond has undertaken a very long journey by the time you see it sparkling in the jewelry case. Diamonds are also very old, millions of years old in fact. The prevailing theory is that they form in the Earth’s mantle at very high temperature and pressure. A white colorless diamond is made of pure carbon and is the hardest natural material on earth. Graphite by contrast is also made of pure carbon, but is commonly used in pencil leads. So how do two substances made of the same material differ so much? The key is the crystal structure. Diamonds are formed in the cubic crystal system with a repeating pattern of 8 atoms equally spaced from each other. This provides a very strong structure for the diamond and is the reason for its hardness. Precious metals like gold and platinum also have a cubic crystal structure which allows for their use in jewelry as well. By contrast, graphite’s crystal structure is similar to a layered honeycomb pattern and lacks the strong bonds between layers of atoms that is present in a cubic system. The strength of the cubic crystal structure is a key part of a diamond withstanding the temperature and pressure of the journey to the earth’s surface.
Diamonds came to the surface during volcanic eruptions that have occurred over the earth’s lifetime. Over hundreds or thousands of years, the volcano subsequently became dormant in order for miners to access the diamonds. No one is trying to extract diamonds from an active volcano! Prospectors would look for a specific type of rock called Kimberlite which can contain diamonds. Kimberlite is named for the town of Kimberley in South Africa. Kimberlite normally occurs in pipes which follow the diamonds track up the interior of the volcano to the earths surface. These pipes can occur on land, or underneath bodies of water as geological changes will certainly have occurred in the surrounding landscape over the thousands or millions of years since the diamonds were brought to the surface.
In additional to finding diamonds in a primary source like a kimberlite pipe, diamonds can also be found in rivers or streams which are referred to as secondary sources. These diamonds have been washed away from their original location to settle into the soil in bodies of water. These are called alluvial deposits. Alluvial deposits can be mined by hand with simple tools, or in very large operations involving ships and a lot of advanced technology. Alluvial diamonds, especially those found in the ocean, can be very valuable as smaller or more delicate diamonds would not survive the journey from their original source to the seabed and would be broken up along the way.
Diamonds can be found in many places on earth, but it’s not always economically viable to extract them from the earth. Diamonds are brought to market as either industrial diamonds or gem quality diamonds. Industrial diamonds are used for things like diamond tipped drills due to their hardness, and as gem quality stones are used in jewelry. The largest diamond producers by volume are Russia, various African countries (Botswana, South Africa, Congo etc), Australia and Canada. This production would include both industrial and gem quality diamonds. The highest value diamonds however come from countries like Namibia (mined off the coast in the Atlantic) Botswana and Canada.
Next time you look at a diamond, take a minute to imagine how old it really is and how long ago it came to the earths surface. It may have rocketed to the surface in a volcanic eruption and then been carried by a river or stream to a lakebed where it was finally held by human hands for the first time. The diamond industry has worked hard in recent years to provide better traceability for diamonds from the time they hit human hands until they hit the store shelves, but there is still a lot of work to be done. Now we know though, that this last step is but a small part of their journey.
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