Is this gem showing extinction or reflections?

[Indylady]

link to Multicolour

What do you guys think?

 

[chrono]

My guess is facet shadowing or some sort of head obstruction. Have you asked MC for confirmation?

 

[innerkitten]

Chrono could be right. Anyway looking at it my first thought is that it is extinction.

 

[Michael_E]

There are only four things which can cause dark zones in gems.
1. Head reflection, (obstruction, shadowing, etc.)
2. Absorption, (extinction), of light along certain axes. This happens in tourmaline, sapphire and other stones which can have ones axes of the crystal structure which is darker than the others.
3. Attenuation, (also extinction), of light due to the light path being too long for a particular color saturation level. In dark colored stones the light will travel so far through the stone that none is getting back to your eyes. This happens in garnet, sapphire, spinel and other stones which are dark and are too large.
4. Reflection and transmission of light from areas where there is no light. This is called "light leakage" over in the diamond area of this forum. It's not so much that the light is "leaking", but that you are seeing areas from behind or to the sides of the stone. A window will cause this in the center of the stone, as will cut angles which cause a "leakage" in dark areas around the perimeter of the stone.

Since spinel is in the cubic crystal structure and has no different light response along different crystal axes it isn't extinction from this cause. Since the stone is lightly saturated, attenuation will cause increased saturation in areas where the light path is longer, (making the color deeper), but not extinction. Leakage is out, since the stone has neither a window nor evenly distributed dark areas in the perimeter. This leaves a reflection of the head of the photographer as an explanation of the dark zones in the stone. I don't like the term "shadowing" very much since a stone can be directly shadowed and still be bright if it's reflecting light from around the object doing the shadowing.

Remember that taking large images of gems is very hard to do and still avoid the effects of head reflection. This is because you either have to get very close to the stone, causing the effects of head reflection to be more pronounced, or you have to be much farther away, use a tripod and zoom in dramatically, requiring equipment and many seller don't have. It's usually a good idea to get a side shot of a stone if you have questions about what's going on, because this will show body color independent of reflections, as well as giving a good view of the depth of the stone.

 

[T L]

IndyLady,
I think it''s head obstruction. However, I would like to add that I think it''s rather high priced for such a pale, desaturated, and very small gem.

 

[LD]

I bought an Apatite from MC a few years ago in the same cut. The advert photo showed exactly the same and it isn''t there IRL so I would say that everybody above has nailed it and it''s some form of obstruction (shadowing) whatever you want to call it!!!!

 

[Indylady]

Date: 1/30/2010 3:25:17 PM
Author: tourmaline_lover
IndyLady,

I think it''s head obstruction. However, I would like to add that I think it''s rather high priced for such a pale, desaturated, and very small gem.

Really? I thought it was a deal! Yikes?

 

[Stone Hunter]

Date: 1/30/2010 3:48:35 PM
Author: IndyLady

Date: 1/30/2010 3:25:17 PM
Author: tourmaline_lover
IndyLady,

I think it''s head obstruction. However, I would like to add that I think it''s rather high priced for such a pale, desaturated, and very small gem.

Really? I thought it was a deal! Yikes?

I think that the price is very dependant on color and maybe the color is super super pale? You could call and ask about it though.

 

[T L]

Date: 1/30/2010 3:48:35 PM
Author: IndyLady

Date: 1/30/2010 3:25:17 PM
Author: tourmaline_lover
IndyLady,

I think it''s head obstruction. However, I would like to add that I think it''s rather high priced for such a pale, desaturated, and very small gem.

Really? I thought it was a deal! Yikes?

It''s a GIA gemset of 2/2 which means it''s extremely desaturated and very light. I doubt even one of our favorite precision cutters like Gene or Barry would sell that stone for that much. It''s also rather small (less than a carat). You can find desaturated pink spinel quite a bit on ebay too. Gem-Earth is a somewhat respected dealer that has them from time to time.