Monday, September 1, 2014

Testing the Blue Moon Diamond at the Smithsonian

The Blue Moon Diamond, a 12-carat Fancy Vivid Blue diamond, on display at NHM. Photo by Tino Hammid for Cora International.

Beginning September 13, 2014, we will have a very special host in the Gem Vault of our Natural History Museum of Los Angeles County: The Blue Moon Diamond will be on display until January 6, 2015. The 29.6 ct rough diamond was found back in January 2014 at the Cullinan Mine in South Africa. Cora International purchased it in February and had it cut in a spectacular 12 ct cushion. The faceting of the stone took place from April to the end of June in New York.

First of all, I wanted to emphasize our interest to have such a stone at our museum. Of course, there is the exhibit point of view. What a great opportunity for our public to be able to see a big blue diamond. Yes, 12.03 ct (2.4 grams) is impressive for a blue diamond. They are much, MUCH rarer than colorless diamonds (called "white diamonds" in the market). They are probably some of the rarest of all the gems. This diamond has been graded by the Gemological Institute of America (GIA) Fancy Vivid Blue diamond, with an IF (internally flawless) quality. The cut is perfect. All of these qualities make it a gem as rare as "once in a blue moon", phrase from which its name comes from.

Now, in the scientific point of view, this diamond might be even more exceptional! I have been studying blue diamonds for over 5 years now, mostly when I was a post doc at the Smithsonian Institution. I had the chance to study famous stones such as the Hope diamond, the Wittelsbach-Graff or the Blue Heart diamonds for example. All in all, it's over 100 blue diamonds that I have analyzed. But most of them were less than one carat, and only a few were of known origin (a dozen only). And they are so rare that we had to find ways to borrow some diamonds for our study. If a few came from the National Gem & Mineral collection, most came from private parties. Aurora Gems for example loaned to us over 3/4 of the stones studied. We are thankful that Cora International agreed to let us conduct some (non-destructive!) analyses on the diamond, and also supported me to go to the Smithsonian to acquire the necessary data.

Why blue diamonds are so special? As explained in a previous blog post, their color comes from the element boron. First interesting fact: boron is quite rare deep in the Earth, where diamonds form (in the Earth Mantle, some 90 miles below the Earth surface or deeper!). Boron is a light element and is expected to be found mostly at the surface of the Earth, or not far below. So, where does the boron contained in the rare blue diamonds come from? Was it in the Earth Mantle since the formation of the Earth? Or was it pushed deep inside the Earth through plate tectonics, by convection of a subducting oceanic plate?
Also, we know that boron gives the blue color of a diamond. But does the amount of boron directly correlates with the intensity of the blue color? Blue diamonds have the property of phosphorescing (emitting a color after exposure to an ultraviolet light - also called black light-). Most emit a very short bluish phosphorescence, while a few emit a orange-red glow. What physical phenomenon controls that?

In this blog post, I'll show you a few pictures of the Blue Moon diamonds acquired while we were conducting the experiments at the Smithsonian Institution, in the highly secured "Blue Room", in the Mineral Sciences department. But look forward to an article talking about the actual results in the coming months!
The scientists present during the experiments were: Dr. Jeff Post, Curator and Dr. Keal Byrne, postdoc, both from the Smithsonian Institution; Dr. Jim Butler and myself.

The arrival of the Blue Moon Diamond and its unpacking by Jeff Post.

Waiting to discover the stone we long expected to see!

Far from being a professional picture, our first look at Blue Moon Diamond. There were a lot of "wow" in the room when Jeff opened the package.

The Blue Moon Diamond and the phosphorescence equipment on the background. 

The diamond is now in place to be analyzed. The metallic wire is a fiber optic that conducts the ultraviolet (UV) light and receives the light emitted by the stone. 

A close-up of the experiment: we analyzed several spots on the stone to see if the diamond was emitting similar phosphorescence everywhere.

Jim preparing a cover for the experiment!

There is nothing to see anymore: the diamond is fully covered to be in the dark during the experiment.

Keal and I doing the last tests before running the phosphorescence experiments. Photo by Jeff Post.

What is it that we are doing when we run a phosphorescence experiment? As Jeff shows to the film crew, it's similar to exposing the diamond to a UV light for 20 sec, turning the UV light off and looking if the stone emits a light and if so, what color light. However, our eyes are not as sensitive as a spectrometer is, that is why we use this machine on top of the visual examination.

A very surprising result: the Blue Moon Diamond phosphoresces orange-red for about 20 seconds, while most blue diamonds show a short bluish phosphorescence. Only a few other diamonds have such a reddish glow, we will cite the Hope diamond and the Wittelsbach-Graff for which the phosphorescence lasts a minute! Amazing photo by Tino Hammid for Cora International.

The exact reason for the long red versus short bluish glow is not perfectly understood. That is also why we continue acquiring data on more blue diamonds. It might involve the boron defects present in the structure of diamond, interacting with other impurities, defects or charge imbalance. So far, the Blue Moon diamond is the only diamond known coming from South Africa that shows a red glow. The other diamonds of known locality showing the red glow were coming from India (such as the Hope diamond or the Wittelsbach-Graff).

We also conducted some experiments with a Fourier Transform infrared (FTIR) spectrometer. With this machine, we can see the signal of the carbon atoms interacting with each other, as well as the signal of the possible other impurities. Photo by Jim Butler.

Getting some signal through a faceted stone is not the easiest! But we got some good results. Photo by Jeff Post.

Our FTIR analyses confirmed the presence of the element boron as an impurity, which is the source of the color. The Blue Moon Diamond is therefore classified as a Type IIb diamond (no nitrogen impurities visible by FTIR, but boron impurities present). We will be able to quantify the amount of boron thanks to the spectra acquired. Stay tuned!

Finally, we were curious to look at the remaining strain inside the diamond structure. All natural diamonds show some strain features, and the Blue Moon is no exception. The colored striations are the evidence of such a strain. Photo: Eloïse Gaillou, in between cross-polarizers.

Again, they are not professional pictures, but I still wanted to end with a few shots that I took while conducting the experiments at the Smithsonian. You will have to come to NHM Los Angeles and see for yourself to get the true experience of the color and the fire of the Blue Moon! Photo below and above: Eloïse Gaillou.

All photo credit: Eloïse Gaillou, unless otherwise mentioned.