irridescence in sapphires?

[Hudson_Hawk]

While looking at a Sapphire ring (about 2 ct) over the weekend I noticed that instead of a deep dark stone there was what looked like an irridescent layer to the stone. The sales person mentioned that it was a natural untreated stone of a "prized" shade of blue but I had never seen the irridescent affect before and I was curious about what it was. Does anyone know? I noticed it when I looked at the stone from an angle. At first I thought the table might just be smudged but it was still there after the saleswoman steamed it.

 

[innerkitten]

Some sort of crystal inclusion or formation maybe? I have a spinel that has a rainbow on it when I view it at a certain angle. Looks like an oil slick.

 

[colorchange]

You will sometime see iridescence coming from discoid fractures, but certainly not in an unheated stone !!!!

If what you saw was rather a kind opalescence as I believe since you are mentioning it comes from the surface, it may come from very small and abundant rutile needles, typically in very light colored sapphires from Burma, Kashmir and Ceylon.
I have a 3 Ct "Kahmir type" that has a very strong opalescence for instance.
That kind of effect is usually seen from every angle.

One last effect that exists is a reflection on "tables" of rutile, seen mostly in Madagascar sapphires, even if you can find some everywhere. The rutiles will form a perfect octagon (indeed a hundred small octagon with parrallel sides and the same center on one single plan). Looking from the righ angle is might create iridescence. Anyway it isn't valuable.

 

[MustangFan]

what is the price of the 2 ct. sapphire?
You can tell a lot from price, and a lot of jewelry stores will tell you what you want to hear I''ve found...

Believe me I hunted for my sapphire for over 3 months and it got hiring after awhile.
I would have been engaged in July if I had just made it easy and gone with a diamond, but it looks like Jan or Feb.

 

[MustangFan]

$1800-$2000 per carat seems to be the going rate for unheated stones, maybe a little cheaper...

My boyfriend bought my sapphire at alittle under $1200 per carat, it is 3.17 carats and is a heated stone. There is nothing wrong with heated stones, mine has some silk but it very lively and bright inside. It definitely has a "WoW" factor in the sunlight.

 

[gemmy1]

It sounds like what you are seeing might be rutile inclusions, aka "silk". They are very fine needle-like inclusions commonly found in sapphire. When they are in abundance they can result in asterism (star sapphire).

Rutile dissolves in sapphire at high temperature. The presence of intact rutile is evidence that the stone is un-heated.

Often, a small amount of silk will be visible as a sort of sheen from certain angles. It can look like a smudge.

Sometimes I notice some irridescence when viewing these inclusions under a microscope. The parrallel linear crystals can act like a diffraction grating and break light up into component colors. I don''t think I have ever seen it with the naked eye though.