Cat's Eye Diamond???
10 May 2016
An interesting mystery from the ISG Journey Thru Gemology
In last week's meeting of the ISG Journey Thru Gemology we talked about the gemstone property of chatoyancy...the "cat eye" effect as seen in this older image from the ISG Archives at left. At right you see why this phenomenon is called "cat's eye" as the eye will open and close when turned in the light source, as demonstrated by this cat's eye enstatite from the ISG Student Reference Collection.
During the preparation for the week's edition of the Journey Thru Gemology I received an email from ISG Global Network Member Joanna Emmett that the company she works with had what they believed was a "chatoyant diamond" they would like for me to evaluate. A what? A Cat's Eye Diamond? I have to admit I had never seen one, which is not to say they are not all over the place, but from my 45 years in this business I cannot say that I had ever seen a true "chatoyant diamond". So my first reaction was...."that's very nice, Joanna, have a nice day." But she did not stop with just an email or phone call, she packed it up and sent it to me for evaluation. Sure enough, for all of the technical jargon that may or may not apply here, this does test by several diamond/moissanite testers on the market to be a chatoyant diamond. Or is it?
Many of you may recall this image from last week's teaser for the Journey Thru Gemology study. A very unique looking diamond that already shows some strange, parallel type formations that are quite often seen in some types of gemstones that demonstrate the phenomenon of chatoyancy.
But did I call it a "cat's eye diamond" too quickly?
Could this be a "cat's eye...something else"???
When you illuminate it with an overhead transmitted fiber optic at just the right direction it shows a very clear cat's eye effect.
Below is another look.
This image was taken with the same overhead fiber optic and a side-directed fiber optic, using our Meiji Techno GEMZ-8TR BFDF microscope.
Here you can clearly see the impact of the parallel inclusions in the gemstone that form up to create the optical effect of the cat's eye.
But are these inclusions or something else? Most chatoyant gemstones are due to parallel formations of things like rutile needles or something similar. What is causing this chatoyant effect here?
Upon closer examination I found these were not needle-like mineral inclusions at all. They are instead empty tubes that exist in perfect parallel structure.
At this point, my friends, I have to admit this is not something I have seen before.
I checked Koivula's PHOTOATLAS of Inclusions in Gemstones....all three editions. Nothing contained in these excellent references showed anything similar to this formation you see at left.
The search continued...
I took more microphotographs with our Meiji Techno microscope, below you see these parallel inclusions at 10x (below left) and the same area under 90x (below right). These are indeed empty tubes as they appear. At this point I went into my safe of special references and pulled out Gary Roskin's Photo Masters for Diamond Grading, once again, nothing comparable. This left the obvious question: Is this really a diamond?
As it has for many years, the Enwave Raman that the ISG Community
and consumers pitched in to help us obtain in the ISG office, paid off.
Please Note:
Here I should also add that the use and study of Raman Spectroscopy is a fast-growing technology for gemology. The ISG offers a basic overview of the study of Raman Technology. However, for the finest study in Raman Spectroscopy and the finest Raman Spectroscope for gemology on the market, I personally recommend the GL Gem Raman from the Canadian Institute of Gemmology and their GemLab Group. For gemology and gem identification, the GL Gem Raman is the most advanced, best supported and most reasonably priced Raman Spectroscope to be found anywhere in the world.
Below are our comparisons of this cat's eye gemstone to our Raman database.
At left is our Raman scan of the diagnostic 1332 cm-1 peak of natural diamond.
Here we have our Raman database scan of a diamond treated with irradiation. The damage to the crystal lattice is reported to be the cause of the "hump" you see, which is due to photoluminescence.
Finally we have a first generation HPHT treated Type I diamond, seen at left. Notice the difference in the three scans of known diamonds and compare to the one below of the cat's eye diamond.
HUGE problems presents at this point: The "cat's eye diamond" is not a diamond at all. What should be a 1332 cm-1 peak is showing but it's more in the 800 cm-1 range. This cannot be diamond.
In fact, this is a rather classic Raman scan for a synthetic moissanite! Which it is. But with some strange twists.
Here is the problem. All of the traditional diamond testers showed this as a diamond. Due to the very heavy concentration and formation of the inclusions, the usually diagnostic doubling of facet junctions seen in synthetic moissanite were virtually impossible to see. It was only going back to our Meiji Techno and using the 90x magnification with zoom focus, and two fiber optic lights to cut through the maze of inclusions that I was able to capture the image you see below of the doubling of the back facet junctions around the culet when viewed through the star facet of the crown.
Hazy appearance of the facet junction doubling of this synthetic moissanite through 90x Meiji Techno with double fiber optic side transmitted lights.
There are many lessons to be learned from this episode:
1- Don't trust those diamond testers on the market that are supposed to separate diamond from synthetic moissanite.
2- Know that there are treated gemstones out there that can and will fool even experienced gemologists.
3- Always confirm your confirmation tests when it comes to identifying gemstones for others.
4- Never hesitate or be afraid to go back and take another look at something you have done.
5- If you find you made an error, correct it and publish it.
Due to time constraints in preparation for the Journey Thru Gemology presentation I honestly missed the location of the Raman peak in the synthetic moissanite. That Raman scan was done just minutes before the presentation started and the misreading was due to being in too big of a hurry. Mea Culpa! It was one of our ISG Students that commented to me that the scan peak was significantly off and another look was warranted, which today I have done.
The answer to the question at the top of the page is simply this: the "cat's eye diamond" is really a cat's eye synthetic moissanite. I have no clue how it got this way, but it is chatoyant. Perhaps someone out there has an explanation on that question. HPHT Synthetic Moissanite? Perhaps someone can answer that.
Many lessons were learned from this amazing gemstone.
In the end...isn't that why we are all here?
Robert James FGA, GG
President, International School of Gemology
http://www.isgglobalnetwork.com/
