I recently send what it seems to be a "true" cat's eye sapphire to AGL. I suspect that the sapphire is in fact a star sapphire that has two extremely fainted leg or a star sapphire that has been creatively cut to focus on one of its leg. Surprisingly, I got call and found out that AGL has concluded that the sapphire is natural cat's eye sapphire. I wonder, what kind of test do you perform to draw such conclusion. I cannot imagine that there exist a corundum which most of its inclusion are parallel to each other such that it form a chatoyancy effect like this
Why not? There's nothing about its crystal structure that would forbid it. This would be pretty darn simple to determine by microscopy I would imagine. By the way, congrats on having such a neat stone. I can't remember if you posted pictures before, but I'd love to see more even if you already have.
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21688 Location: San Francisco
I recall Richard Hughes mentioning this somewhere, a long time ago. As I recall, if a sapphire has many planes of inclusions along the basal plane, if the cabochon is cut with the base parallel to the C axis, one will get a stone which appears chatoyant.
Joined: Fri May 12, 2006 11:24 am Posts: 7525 Location: Rome, Italy
Barbra Voltaire wrote:
As I recall, if a sapphire has many planes of inclusions along the basal plane, if the cabochon is cut with the base parallel to the C axis, one will get a stone which appears chatoyant.
If it's just a normal star sapphire cut perpendicular to the star, it will only look like a cat's eye when viewed directly from the top. Turn the stone and view it from the side and at least some of the other legs should appear.
Joined: Thu Feb 22, 2007 10:23 am Posts: 948 Location: NYC
LiYou wrote:
does it mean every star sapphire can be cut to produce a chatoyant effect? What do you mean by "many planes of inclusion"? please, enlighten me
by plane of inclusion it means The Chatoyant Bands which intersect at 60°.
Depending on the Rough and weak bands the cutter decides to go for star or cat's eye. if one cut along with C axis the Chatoyant band will be in top of the cabochon dome, you might see other bands in sides.
also in some cases the star might be too off center and located in sides so basically you still see a cat's eye along the dome and star in one side, something like this picture but more off center
Attachment:
Chatoyant Gems.jpg [ 5.29 KiB | Viewed 27907 times ]
does it mean every star sapphire can be cut to produce a chatoyant effect? What do you mean by "many planes of inclusion"? please, enlighten me
by plane of inclusion it means The Chatoyant Bands which intersect at 60°.
Depending on the Rough and weak bands the cutter decides to go for star or cat's eye. if one cut along with C axis the Chatoyant band will be in top of the cabochon dome, you might see other bands in sides.
also in some cases the star might be too off center and located in sides so basically you still see a cat's eye along the dome and star in one side, something like this picture but more off center
Attachment:
Chatoyant Gems.jpg
are you implying, if the cutter cut along with C axis, the stone will appear to exhibit cat's eye effect. However, you can still observe the other leg of the star on the stone?
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21688 Location: San Francisco
I believe we are answering your question. "Cat's eye Sapphire conclusion?"
If a sapphire xl possesses 3 planes of inclusions appearing like this when viewing down the c axis, A star stone can be cut when the bottom of the cabochon is perpendicular to the direction of the c axis. Looking down parallel to the "c" axis: producing In this view, the orientation of the planes of needles reflect light to form a regular six-rayed star;
If we placed the base of the cabochon, parallel to the direction of the "C" axis the inclusions would appear to be oriented in only one direction, therefore, only one strong light band would be seen in the center of the cabochon. Voila! Chatoyancy!
if that is the case, why cat's eye sapphire is significantly rarer than star sapphire? unless all star sapphire cutters throughout the world form a perfect cartel, there is no way that cat's eye sapphire rarely available in the market.
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21688 Location: San Francisco
It's not a matter of rarity, it is a matter of saleability. Star stones are far more desirable than cat's eye sapphires, therefore they command higher prices. I suspect the original xl of the sapphire you possess had a defect which made cutting a star impossible or unrealistic..... It's likely every crystal ending up as a chatoyant sapphire had a a structural issue which would have either produced a star decidedly off center without significant weight loss, or worse......no star possible at all.
LiYou, you are asking for information but disputing everything told to you. I know you would prefer hearing, "You may possess the most valuable phenomenal sapphire in the world. Lucky LiYou!!!!"
(That said, I'm not giving up hope on a non-star chatoyant sapphire! Not necessarily in this case but in some case. No reason it couldn't happen, even if it's obviously not common.)
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21688 Location: San Francisco
Scarodactyl.....they do exist. But it is a function of the lapidary, not the mineralogy. Think of the xl. Think of the orientation of inclusions......have you ever seen an inclusion scene in corundum with all fibrous inclusions in one plane, in one direction? That would be weird.
Doesn't count if it's just a miscut star imo. I suspect the other legs would be evident from some angles, and anyway it's not the same in my book.
Barbra Voltaire wrote:
Think of the xl. Think of the orientation of inclusions......have you ever seen an inclusion scene in corundum with all fibrous inclusions in one plane, in one direction? That would be weird.
Yup, it sure would be weird! Unheard of, even. Which is rather the point for me. I doubt I'll come across one, but I suspect one probably exists somewhere.
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21688 Location: San Francisco
Fair enough.....you are probably right, such a sample exists. I bet it was cut in such a way that the inclusions don't show up well in a face up direction.
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But it is a function of the lapidary, not the mineralogy. 
