crackle

This is a very cool pearl! Even if it was poorly treated, I think the result is a happy accident. Neat collection item!
 
Thanks. I've seen my fair share of poor Tahitians, but I can't say I've ever seen one that looks as if it's been burned. I do know what a burned one looks like...a little "experiment" with a keshi!
Ugh, it's so hard to describe. It's like a black hole in the nacre, but not like a clean hole from drilling ... more jagged. It's missing nacre with concentrated conchioline and other organic matter. The rim of the "hole" often has a whitish coloration too. It's like a little bomb went off on the surface, lol.

I can picture this in my mind easily, but even going on Google image search, I can't see to find one.
 
Darn. I don't have a photo, but I know what you are talking about.
 
This is a photo of some Tahitians I pulled off an old thread on PS. I do not own these pearls so can't supply any more photos.

I don't thnk this is the kind of flaw you are referring to, but what exactly are the white spots in the pearl on the right? Is it just that that's the color of the nacre there? The large divot in the pearl on the left also looks white inside.
 

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Those are different flaws and wouldn't preclude the pearls from export. Now I have to find one to post a photo. It might not be until the next trip though.
 
To be a little more elaborate, I'll include the material produced by the e-cells during their respective period in the growth cycle.

periostracial (conchiolin) -> prismatic (calcite) -> nacreous (aragonite)

Not all mollusks though. In the case of scallops or some gastropods it's:

periostracial (conchiolin) -> prismatic (calcite) -> foliated (calcite)

In nautilus and other gastropods it's:

periostracial (conchiolin) -> prismatic (calcite) -> columnar (aragonite)

Technically, there's actually four layers, but only in over-mature shells. Pearls are harvested young.

periostracial (conchiolin) -> prismatic (calcite) -> nacreous (aragonite) -> calcitic (calcite)
 
Here's a diagram I drew up a few years ago. It defines shell structure in all mollusks.
 

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Agreed! One way to look at it in a more simple form is that a pearl is a lot like the shell, except backward. The periostracum is the outside of a mollusk shell and the nacreous layer is the innermost side. Pearls are in some ways, mollusk shells inside out.
 
Dave - Thank you for that excellent explanation !!

Jeremy - Oh I do like that description !

I agree wholeheartedly: Dave's explanation and diagram are superb! And Jeremy's description of how the shell and the pearl are the inverse of each other...simply magic!
 
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