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The Arabic naqur (mollusk shell) is turning out to be a prescient etymology. It would be of great interest to know if you would offer any guidance for Elizabeth Strack on a future update to her comments on nacre. She's one of the most open-minded gemologists I've had the pleasure of meeting!

Should this contain a link?

The nacreous and porcelainous microstructures co-exist within the same shell but preserve their distinct morphologies.

We have discussed "burdens" previously, above. Here I argue that the "common knowledge" being changed (burdened?) is the predominant concept of nacre as the miraculously iridescent 5% organic microstructure with which we are all familiar. Without a more generic overarching term for the...

I like it. I also see that the bulk of the cited research post-dates my time at the SEM in Granada, 2011-2013. It still seems a stretch to apply the term 'nacre', so broadly. Neither do you see such reference in the literature. You would be better than me at finding a more generic term for the...

The equivalencies you are drawing make common usage of the term 'nacreous' as obsolete as the term 'non-nacreous.' Who's going to rewrite the book?

If there is anything in the scientific literature that concisely and transparently defines nacre in such a manner I would want to be the first to see it.

At this point we must agree to disagree. I will be sticking with the terraced/columnar organic secretion models that result in iridescent phenomenon. But will happily campaign for the true-pearl status of 'porcelanous/porcellanous/porcelainous' specimens.

OK so per Douglas' suggestion above, what would be the percentage? The aragonite platelet model of nacre would be differentiated by its organic component. If only our unidentified porcelainous pearls had such a layer!

Yes the low organic component of crossed-lamellar shell material has frustrated all our attempts at genetic extraction for pearl species confirmation. But the issue of 'degree of nacreousness' is still eluding us. What percentage should be assigned to crossed-lamellar shell material, assuming...

This is a very helpful observation. It is still not clear how we can speak of percentages or degrees of nacreousnous. Whether expressing as iridescence or not, nacre is nonetheless nacre. "It either is, or isn't, nacre." My conclusion here is that a crossed-lamellar pearl such as Conch that is...

Are these percentages / degrees of nacreousness referring to the distribution of microstructures throughout the different regions and layers of a shell? If not, can we clarify how nacre, crossed lamellar, prismatic, etc can be secreted together as a homogenous amalgam?

Once again we are dealing with ambiguity that defies understanding. Terraced or columnar aragonite platelets, carefully organized and secreted by the mantle, comprise nacre. It either is, or isn't, nacre. Crossed-lamellar is the anti-nacre, perhaps even the prototypical 'porcelainous'...

I am continuing to have difficulty with the ambiguity. "Highly Nacreous" suggests that there are degrees of nacreous expression, such as "Moderately" or (dare I say) "Non." Aragonite tablets/platelets arranged in terraced (Bivalvia, Cephalopoda) and columnar (Gastropoda, Cephalopoda) forms...

Porcelanous/Porcellanous/Porcelaineous. I was going to include the third English spelling option but was afraid of too many slashes! In all due respect, I do not think it is clear to anyone but a biomaterial scientist (and that does not include me!) about the nature of nacre vs. porcelaineous...

The point is that nacreous refers to all mollusk shell construction resulting from an organic process preceding and directing tablet and fibre crystallization? I just looked up etymology for nacre and among its possible origins is the Arabic naqur (hunting horn), the shape of a mollusk shell...

The assertion is effectively and empirically refuted. It seems as though it comes down to who has the burden of proof (as in a court of law), the gemmological sector having reached its conclusions. We need to organize!

Dave, You will be anticipating this post… Below is a report from Nature (10/17/1912) regarding the pearl gifted to T.H. Haynes (pioneering Australian pearler) by the Sultanate of Sulu in 1884. As all such reports over the centuries of pearls from the 'pearly' Nautilus, it was porcelanous and...

Is this the interpretation of FW shell beads from mussel? While colorless and non-iridescent, they are regarded as nacreous and thus compatible as nuclei (although now it seems the range of successful nucleus material is wider than long thought). Is an argument in favor of the existence of...

Fantastic post! On the above statement, where would 'highly aragonitic' fit in? I'm thinking about non-nacreous aragonite/calcite microstructure generally referenced as crossed-lamellar and characteristic of the 'flame' phenomenon. No doubt my thinking could use updating…