A New Reason to Buy Diamonds

By Megan Reynolds, AJP (GIA)

So, we know that diamonds are beautiful and can be used in all sorts of things from beautiful jewelry to precision scalpel blades. However, a pair of researchers has dreamed up a whole new use for those sparkly gems that we love so much. Researchers Steven Shirey and Stephen Richardson had the idea that inclusions locked within diamonds could be used to date the diamonds themselves, as well as to get a glimpse into what Earth may have looked like billions of years ago.

Think of it like this. Remember the movie Jurassic Park? Well early on in the movie, before all of the dinosaurs went rogue and started eating everything in sight, there was a scene set in an amber mine. The scientist was shown a piece of amber with a small, perfectly preserved mosquito trapped inside, and from that mosquito, they were able to extract dinosaur DNA. And then, as I said earlier, a lot of people got eaten. But I’m drifting off point. 

Photo: Didier Desouens

With this research Shirey sought to answer an age old question, “how far can we extend the current knowledge of processes that shaped the surface of the earth”? Well, thanks to diamonds, pretty far.  Diamonds form deep underground, under immense temperature and pressure and are then catapulted to the surface via violent eruptions. This is an amazing thing when you think about the fact that if the temperature and pressure aren’t exactly right, or it takes too long for the diamond to reach the surface, all that’s left is graphite. And while graphite is super useful in a #2 pencil, it’s not really all that lovely, or helpful to our researchers.  They were more interested in when everything did go right.  You see, when a diamond forms, it can form around various other minerals, thus trapping and preserving them forever. Much like the mosquito we were discussing earlier, these impurities were essentially frozen in time. They remain exactly the same as the day they were interred, like mini time capsules. This phenomenon is the key, since most of the rocks of that age are either trapped miles underground, or have been destroyed by the ravages of time, which make the mineral inclusions within diamonds an invaluable source of information.

So, this is great, Shirey and Richardson had an easily accessible subject matter and could get straight to work. Well, not quite. It turns out that research isn’t cheap, and purchasing a large quantity of diamonds ranging from .5 to 1 carat just wasn’t a possibility. Also, finding diamonds with the right types of inclusions was a bit like finding a needle in a haystack. It took three years for the duo to obtain just ten diamonds of the correct size, and having the proper type of inclusions worth studying. The pair also used previously published data on more than four thousand silicate inclusions and around one hundred sulfide inclusions to round out their results.

Now that the researchers had their stones, the real work could begin. The first task, sadly, was to take a laser and cut into the diamond to harvest the tiny inclusions. Once the particles had been collected, they were placed into a mass spectrometer for analysis. Now a mass spectrometer is a machine that scans a sample and tells you exactly what it is composed of. It’s the same type of machine that they use on the TV show CSI. They feed an unknown substance in, out pops a sheet of data that says the substance has specific chemicals in it, and they immediately recognize it as a very obscure hand cream, meaning that the butler did it! Yeah, that part always seemed a bit far-fetched for me as well, but the science is sound. Anyways, back to our researchers. Using that data from the mass spectrometer, the researchers could then date the samples to see when they were locked within the diamond.

For example, diamonds form from carbon released by either peridotite or eclogite rock when it melts, miles below the surface of the earth. When the diamond forms, it sometimes forms around a tiny piece of its host rock. Using the mass spectrometer, our researchers were able to tell exactly which host rock that the diamond formed around, thus dating the diamond. They discovered that before 3.2 Ga (Geologic Age), only diamonds with peridotitic inclusions were found, however after 3.0 Ga, diamonds with eclogitic inclusions were found. This means, that somewhere in between 3.2 and 3.0 Ga, something happened to the structure of the earth. Shirey and Richardson hypothesize that this change was caused by the beginning of the Wilson Cycle, which is the cyclical opening and closing of ocean basins caused by the movement of the earth’s plates. This causes something called subduction, where one plate runs into the other forcing an overlap. As one plate is forced under the surface of the other, it dissolves and its contents (including eclogite rock) are redistributed. This process causes the eclogite to release carbon, making diamond formation possible. According to their theory, the eclogite diamonds formed after the beginning of the Wilson cycle, and peridotitic diamonds formed before, allowing the Wilson cycle to be dated in a way that it never has been before.

Unfortunately, as so often happens with science, we can’t be certain that the Wilson cycle had begun by 3.0 Ga. We simply don’t know enough to be sure that plate tectonics, as we know them today were in action at that point. However, the data obtained by Shirey and Richardson is a big step in the right direction. The duo now hope to study diamonds from other areas of the earth to see if the data obtained is different based on geographic location. Only time will tell, but I know one thing for sure, they’re not getting their laser wielding hands on my diamonds!