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I would read that paper, if it even exists. Meaning no disrespect to Laurent, it's an opinion not an established fact. If his lab is interested in investigating this, I will contribute specimens for analysis. I have presented photographic evidence of sand implicated in pearls. Surely you don't...

They sure are! I'm astonished clams don't produce more pearls. I suppose because they live within substrate they're better equipped to deal with mud, sand and gravel. I don't know how many steamers (Venerupis philippinarium) I've eaten in my day, but it's a lot and I've never found a decent...

There remains confusion whether sand is implicated in the formation of natural pearls. For over a century, the myth has been most pearls are formed around grains of sand. This is a myth. It's been reported in more recent times that grains of sand are not implicated in pearl formation. This is...

I disagree. Sand is implicated in natural pearl onset.

These blisters are formed under the adductor of the left valve. They're not rare, in fact quite common across many molluscan species. They are largely idiopathic (unknown cause) however these present along the medial aspect of the muscle scar as opposed to entirely surrounding it, thus ruling...

Jeremy has included an early natural freshwater strand for comparison, which is clearly that. Graded for size (graduation) first, then luster, color and shape by lessening degrees. Each markedly dissimilar at the nuclei. This is what we'd expect from most natural strands, especially ones created...

Commercial or recreational? Licensed by the state Department of Marine Resources? Recreational harvesting may complicate matters. These are natural quahog pearls, hence the species of origin is not in question. However, some value (albeit scientific) is lost when the pearl is removed. I would...

??

This is not a pearl by any description. More likely a slingshot round.

You have done well given your tools. Each of these views reveal subsurface contrasts consistent with bead nucleated pearls. This is otherwise known as periostracial growth. It's the first growth expressed by most molluscs in any shell building process. It's mainly protein which generally...

Though the images are improving, I'm still seeing equal diffusion at the subsurface and complete absence of distinct contrasting at the nucleus. For those reasons, I'll suggest this is a bead nucleated cultured pearl. Nevertheless, it's a large, well formed SS pearl in good condition.

Thank you, Douglas. Are your naturals P.sterna? I'd really like to see an array of views from those and other species. Same for Gulf pearls, if anyone is inclined to that. Surely someone somewhere has a lot suitable for the task. If anything, this technique demonstrates dissimilar contrasts...

And a few others.

Thank you! A few more.

It's a good start. The first image not so much, the second not as bad and the third is somewhat better. First glances of the second and third image shows a patch of conchiolin just below the surface. While I can't see distinct geometry at the edges of the pearl, I'm leaning toward bead...

And a few more

I've updated the OP and here's a few more.

GIA is a good option, as is SSEF. Both use well defined x-ray views to examine an object. In this case, likely different views to determine the presence of a shell bead. In the absence of that, they'd look at the inner volume for the presence of grafted tissue, geometry of growth stages, foreign...

I would normally refer you to this thread, but it seems the images are different from what I've posted. Forum software update bug, perhaps? Candling reveals the nucleus. There are marked differences between natural and cultural formation. Views of bead nucleated pearls typically show juvenile...

Appraisal is subjective and you'd find a wide range of opinions in the absence of true expertise. 11-12mm is quite large for a natural pearl. That's bad and good. Bad being it's likely cultured, good being it will have some value if deemed natural. The provenance of this piece is questionable...