Diamonds have long been the sign of love and commitment. Being the hardest gem, diamonds are nature’s greatest phenomenon. The diamond industry has proven time and again the trade is dynamic, and available to its widest consumer base yet. Let’s delve into what a diamond is and what has maintained its allure for centuries!

What is a Diamond?

In the mineral world, diamonds are especially unique, being the only gem made of only one element: carbon. Interestingly, another mineral contains only carbon, and is so soft you’re able to write with it. That mineral is graphite. Diamonds can have trace elements that can influence color. Trace elements are atoms that are not part of its characteristic chemical composition. A diamonds crystal structure is isometric, where the carbon atoms bond the same in all directions, making diamonds the hardest mineral.

How do Diamonds form?

For diamonds to form in nature, high temperature and high pressure must be the perfect combination, along with an ample amount of carbon. Diamonds form in cratons, which are located only under the continental crust of the earth. Diamonds have been found to form in Peridotite (an igneous rock) or Eclogite (a metamorphic rock). The conditions for diamonds to form exist approximately 90 to 140 miles beneath earth’s surface.

Key tERMS
Craton — Stable block of the earth’s continental crust and uppermost mantle.
Igneous Rock — Rock formed from cooling of molten state.
Metamorphic Rock — Rock formed from transformation of existing rock to new rocks through heat and pressure.
Chemical Composition — identity, arrangement, and ratio of chemical elements making up a compound.

How do we know where to mine diamonds?

Diamond deposits are found in two types of rock: kimberlite and lamproite. The main difference between the two is that lamproite is typically found on the edge of cratons, while kimberlite is usually found in the middle. Diamonds do not form in these types of rocks, rather these rocks transport diamonds to the surface. Most diamond bearing deposits have been found in kimberlites.

How Do diamonds reach the surface?

Once kimberlite or lamproite are formed in the crust, pressure and heat move the rock upward forming a “pipe.” As these rocks move upwards, they will pick up and carry any formed diamonds from the cratons they pass. The rapid expansion of gasses is what delivers the diamonds to the surface. Scientists have estimated that this process can reach a top speed of about 186 miles per hour. The most important part of this journey is that diamonds maintain consistent temperature and pressure. If exposed to high temperatures and a lower pressure too long, the diamond will convert to graphite. This process has the biggest impact on diamonds being gem quality and is what has contributed to them being considered rare. Once to the surface, most diamonds remain embedded in rock within the pipes, till they are mined.

How are diamonds mined?

There are different ways to mine diamonds, two that are predominately used. One way is “open-pit mining.” This is when there is a primary deposit, and the diamonds are embedded in rock. This type of mining is digging and removing large amounts of surrounding diamond bearing ore. The depth of an open-pit operation depends on the location and size of the pipe, as well as the quantity of diamonds. Once a certain depth is reached, it is better and more cost effective to switch to underground mining. Underground mining consists of horizontal tunnels called drifts used to extract the rock and diamonds. There are vertical shafts drilled to allow the transport of miners and equipment. Once the diamond containing rock is excavated it goes through processes to separate and clean it, so it can be sorted by hand.

Another type of mining is called alluvial mining which occurs on a secondary deposit. This type happens when a pipe has reached the surface of earth and due to natural erosion and weather, diamonds are carried away to nearby rivers or streams. This is where you probably envision people standing and sieving/panning river rock to find diamonds.

Where are diamonds mined?

Diamonds have been found on every continent, except Antarctica. However, mining is difficult and expensive, so profitable diamond mines are rare. Every event must line up perfect to provide a gem quality diamond producing source. To review, there must be all of the following:

Proper temperature, heat, and carbon
Right location to be transported by kimberlite or lamproite.
Survive transportation to discoverable location.
Must be enough diamond rough of gem quality to support a mine.

What happens next?

Understanding the science behind diamond formation makes their beauty even more mesmerizing. Next week, “Part Two” will delve into what happens after diamonds are mined, where they go, and how they end up in a jewelry store.

Natural Diamonds: From Mine to Market PART 1