Despite a famous slogan ‘A diamond is forever’ developed by De Beers marketing strategy back in 1940’s, scientific research proves this statement to be somewhat incorrect these days.
Older then dinosaurs and almost as old as Earth itself, diamonds are windows into the mysteries of our planet’s geologic evolution. How old are the diamonds and are they still forming now?
As we know, the age of the Earth is about 4.56 billion years old and the oldest diamonds that have been dated are 3.5 billion years old, which means the diamonds were forming deep in the mantle even before our atmosphere had oxygen in it. However, not all diamonds are billion years old, the youngest ones are dated to 90-60 million years old, formed prior to dinosaurs extinction. So in terms of the age and human life span, diamonds are forever.
How Diamonds form?
The Earth consists of three main layers: the crust, mantle and core. The majority of the diamonds we see today come from the mantle of the Earth below the cratons ( the ancient continents that has been stable for billion of years). They form at the depth of 90 to 140 miles below the surface and are being delivered to the surface by kimberlite eruptions, which are originated deep in the Earth and are extremely explosive, much more explosive then the volcano’s eruptions (scientists estimate that at the speed of 186 miles/ hour they can potentially reach the surface within the hours). The last kimberlite diamond bearing eruption was documented about 20 million years ago in Australia, which later became a diamond mine.
Some diamond mines, such as Ekati in Canada, have a few generations of diamonds brought to the surface by the same kimberlite eruption, and some mines include one generation ( the example is famous Argyle mine with diamonds dated about 1.6 billion years old)
Why Diamond Age is so important?
Because diamonds form at the great depth of the Earth, much deeper then any other gemstones, it is possible to learn about geological processes within the Earth by dating diamonds.
The problem with dating a diamond is that it is purely made of carbon and has no radioactive elements in sufficient concentration to determine its age. If diamonds didn’t have any inclusions, it would be impossible to date them. Inclusions contain radioactive elements that decay at set rates. For such studies, the inclusion needs to be composited from the diamond. This is quite a distractive process in which diamond is being placed in a diamond cracker and hit by a hammer ( here is the spoiler alert- diamonds can be destroyed). Chemical analysis of inclusions are done in the lab and very time consuming. There are only 2-3 labs in the world that can do this type of meticulous work and set up for this type of technique, and they require a lot of funding.
The diamond ages allows us to access information about the geological processes in the Earth that would not be obtainable other way, for a example: how continents are constructed; how the mantle root below continents form; how it is modified during mountain building ; where diamond fluids come from and how they get there.
Can diamonds be destroyed? Are they not forever?
There are numbers of different mechanisms that break a diamond naturally.
Diamonds can be destroyed, which is important to remember when wearing a diamond jewelry ( a diamond can be scratched by another diamond). Every diamond has a cleavage direction in which it can be broken, knowing this cleavage point is being used in a diamond cutting process.
The most common form of diamond distraction is dissolution or fluid resorption. This process happens deep in the Earth even prior to the eruption, significantly decreasing the size of the diamonds. Fluids start to dissolve the diamond along its edges and form a lot of surface features that we see on the rough diamonds. Often more of 45% of diamond volume gets dissolved this way.
Some other ways that can destroy diamonds are natural geological processes that are happening deep in the Earth, such as extreme heating in the lithosphere or the process of diamonds being graphitized.
While carbon that is needed for diamond formation is always present, (which means diamonds might be forming as you read this), they might wait for millions of years before a violent eruption brings them to the surface. Understanding diamond formation helps us to appreciate how unique diamonds really are.