Call for Industry Adoption: The Aragonitic Scale for Pearl Classification

[Lagoon Island Pearls]

Call for Industry Adoption: The Aragonitic Scale for Pearl Classification

A Necessary Evolution in Pearl Classification

For centuries, pearls have been classified under a rigid nacreous vs. non-nacreous framework. This outdated system fails to acknowledge the continuum of aragonite deposition in pearls, leading to misclassification, undervaluation, and a lack of scientific accuracy.

Current pearl classification is based primarily on optical properties such as orient and luster, which are subjective and do not fully account for the aragonite-based biomineralization present in most mollusk-produced pearls. To address this, we propose adopting a scientifically grounded "Aragonitic Scale" that evaluates pearls based on their structural composition rather than limiting classifications to whether or not they exhibit layered tablets of nacre.

The Aragonitic Scale: A Structural Approach

Instead of a binary nacreous/non-nacreous distinction, the Aragonitic Scale introduces a more precise, mineral-based classification system:

Highly Aragonitic Pearls
Characterized by fine, layered aragonite platelets with conchiolin, producing high luster and orient.
Examples: Akoya, South Sea, Tahitian, and most freshwater pearls.

Moderately Aragonitic Pearls
Contain aragonite layers that are thicker, less uniform, or less optically active but still maintain structural integrity.
Examples: Mussel pearls and certain pink conch pearls.

Slightly Aragonitic Pearls
Comprised of dense, (massive) aragonitic crystalization rather than fine termination and layering, resulting in a porcelaneous texture with minimal optical effects.
Examples: Most giant clam, quahog, conch, and melo pearls.

Other classifications for consideration and inclusion: Calcareous and/or Proteinaceous pearls.

Why the Aragonitic Scale is Crucial for the Pearl Industry

1- Scientific Integrity – The Aragonitic Scale is based on modern research, SEM imaging, and X-ray diffraction, confirming that all pearls contain aragonite to some degree, thus challenging outdated definitions.

2- More Accurate Valuation – Many rare pearls (e.g., clam, snail and scallop pearls) are undervalued due to their classification as "non-nacreous," despite their aragonite-based structures. This new scale provides a structured, science-based approach to description and pricing.

3- Recognition of Rare Pearls – Pearls outside the traditional nacreous group have been marginalized in gemology, despite their historical and cultural significance. The Aragonitic Scale ensures a fair, accurate classification for all pearl types.

4- Market Transparency – The trade, collectors, and jewelers will benefit from a clearer, more precise classification system, reducing confusion over what defines a pearl’s value.

A Call to Action: Industry-Wide Adoption

We urge gemological institutions, researchers, and pearl industry professionals to:

A- Conduct further studies on the aragonite structures in all pearl types.
B- Revise outdated classification models to reflect modern mineralogical findings.
C- Recognize the Aragonitic Scale as a standardized framework for pearl classification.

By implementing this classification system, the industry can better reflect the diversity of natural pearls, improve consumer trust and ensure accurate valuation in the global market. The adoption of an Aragonitic Scale marks a necessary step toward a more scientifically sound and transparent pearl trade.

 

[Lagoon Island Pearls]

This is a first draft, hence incomplete. I invite your commentary and criticism that this may be refined.

 

[SteveM]

This is welcome followup to your previous thread on the subject.

Two comments:

1. Valuation and transparency: The argument will be raised that pearls currently considered 'non-nacreous' include some of the most valuable of all when optical phenomenae, shape, size and color align. Primary examples: Melo melo and conch.

2. Highly aragonitic: The platelet/conchiolin morphology would seemingly result in a lower aragonitic content when compared to the less-organic crossed-lamellar expression typical of the 'non-nacreous' category.

 

[Lagoon Island Pearls]

This is welcome followup to your previous thread on the subject.

Two comments:

1. Valuation and transparency: The argument will be raised that pearls currently considered 'non-nacreous' include some of the most valuable of all when optical phenomenae, shape, size and color align. Primary examples: Melo melo and conch.

2. Highly aragonitic: The platelet/conchiolin morphology would seemingly result in a lower aragonitic content when compared to the less-organic crossed-lamellar expression typical of the 'non-nacreous' category.

As to point 1, changing the classification from non-nacreous to slightly or moderate aragonite ought not imply a change in valuation in most cases. Of course, there are outliers. I'm not entirely familiar with variations in melo melo, thus unable to speak to aragonitic scale, but can with respect to conch pearls which are widely varied. In this sense a more nacreous pearl may support greater evaluation as opposed to those which are lesser in the same species. The scale must also consider the degree of calcite present, which after all tends to greatly devalue objects among the same species. I concede to your point where exceptions exist, but not as the rule. Hence supporting the need for greater clarity on either.

The proposal stipulates this. Although yet perfected, this new scale provides a structured, science-based approach to description and pricing as opposed to a work around of myths or misconceptions.

And point 2, cross-lamellar is technically a nacreous structure, especially where the presence of aragonite is concerned. The term "non-nacreous" erroneously suggests the complete absence of aragonite, thus an incorrect term dispelled by a revised classification system. Even species which are largely structured by foliated calcite have nacreous structures at the base and level of the adductor muscles. Pearls formed in the "vestibular" mantle spaces are highly nacreous, often more translucent (even nearly transparent) than other highly aragonitic "pallial" pearls. High quality cultured pearls contain prismatic and/or reverted calcite. In the case of SoC pearls, flouresence suggests a higher percentage of calcite present than most commercial or some natural pearls. Again, these differences should not effect value by default, instead as a point of reason for determination the value of each.

 

[SteveM]

As to point 1, changing the classification from non-nacreous to slightly or moderate aragonite ought not imply a change in valuation in most cases. Of course, there are outliers. I'm not entirely familiar with variations in melo melo, thus unable to speak to aragonitic scale, but can with respect to conch pearls which are widely varied. In this sense a more nacreous pearl may support greater evaluation as opposed to those which are lesser in the same species. The scale must also consider the degree of calcite present, which after all tends to greatly devalue objects among the same species. I concede to your point where exceptions exist, but not as the rule. Hence supporting the need for greater clarity on either.

The proposal stipulates this. Although yet perfected, this new scale provides a structured, science-based approach to description and pricing as opposed to a work around of myths or misconceptions.

And point 2, cross-lamellar is technically a nacreous structure, especially where the presence of aragonite is concerned. The term "non-nacreous" erroneously suggests the complete absence of aragonite, thus an incorrect term dispelled by a revised classification system. Even species which are largely structured by foliated calcite have nacreous structures at the base and level of the adductor muscles. Pearls formed in the "vestibular" mantle spaces are highly nacreous, often more translucent (even nearly transparent) than other highly aragonitic "pallial" pearls. High quality cultured pearls contain prismatic and/or reverted calcite. In the case of SoC pearls, flouresence suggests a higher percentage of calcite present than most commercial or some natural pearls. Again, these differences should not effect value by default, instead as a point of reason for determination the value of each.

The understanding of nacre as aragonite platelets arranged within an organic matrix in terraced or columnar patterns (thus iridescent) appears to be at issue. I am still missing what logic there is in expanding its popular definition to non-iridescent calcium carbonate microstructures. This issue had my full attention years ago when seeking to explain (or justify) the formation of non-iridescent concretions in iridescent shells (and vice versa), but from a pearl grading standpoint it is not clear.

The challenge is to interface such scientific knowledge of the processes with an aesthetics-based market.

 

[Lagoon Island Pearls]

The challenge is to interface such scientific knowledge of the processes with an aesthetics-based market.

I agree to the extent if were exclusive to that. However, gemology isn't though, it's based on the evolution and acceptance of science not perpetuating myths or giving up. Nacre isn't my only issue with the labs. The absence of proper postmortem analysis is limited to hamstringing themselves, narrow exemplars and opinion. They presume all (or most) pearls are pallial in onset, but we know with certainty there are others.

For example, let's revisit the thread from a week or so ago where bright highly nacreous pearls were found attached to a highly calcareous edible oyster shell. Had these not been attached and submitted to the lab as loose pearls, they'd be lost in the wilderness as to ID. They'd likely conclude natural origin by x-ray analysis, but that's where certainty would end. However, had they developed a library of exemplars based on crystalline micro-structures of common pearl producing mollusks at all levels, they'd be closer to the mark with identification. After all, the differences between vestibular and pallial pearls are better understood nowadays, especially when it comes to measurable differences in the presence of calcitic structures.
Pallial pearl growth patterns are more affected by the otherwise physical functions of the greater mantle than vestibular pearls. As such the phases of growth are sometimes interrupted (I recall your mocking this many years ago) or altered periodically, even radically due to environmental stresses. In the vestibules it's to a lesser degree or not at all, despite being erupted eventually. The labs reasoning for the most part can be substantiated by the lack of live, in situ specimens. Living tissues with pearls sacs are not impossible nor impractical to acquire, in fact it's quite simple because I can produce highly nacreous natural pearls within live creatures on demand, year round. My work with Ana at the lab in Spain recognized this, but the gem labs turn a blind eye. They undoubtedly have the right equipment and the expertise to do so, but choose to remain oblivious. Moreover, the tiniest of micro pearls reveal the true causes of pearl genesis at a cellular level. It seems bizarre they have no interest, to be honest.

Pearl onsets are not limited to pallial or vestibular mantles either. There are visceral and byssal pearls (among others) as well. Each have distinctive if not unique mineral micro-structures.

This issue had my full attention years ago when seeking to explain (or justify) the formation of non-iridescent concretions in iridescent shells (and vice versa), but from a pearl grading standpoint it is not clear.

I get that, but it's becoming more clear over time, albeit slow and frustrating.

While I understand the status quo is just that, it's lazy and indifferent. Present company excluded (of course), because I know your heart of hearts follows this issue keenly. I value your opinion and realistic approaches all the same. Thank you kindly for that. Science however, knows no bounds thus I'm only limited by my resources, not my vision, failures or findings.

A thorn in the side eventually gets the attention it imposed.

 

[SteveM]

For example, let's revisit the thread from a week or so ago where bright highly nacreous pearls were found attached to a highly calcareous edible oyster shell. Had these not been attached and submitted to the lab as loose pearls, they'd be lost in the wilderness as to ID.

That was among the most spectacular and relevant mollusk/pearl specimens ever posted at P-G. Yet, if the purpose of applied science is ID, it is doubtful the financial incentive exists.

Your blow-softening comments are greatly appreciated, likewise your efforts and knowledge have my entire respect. Are you still in touch with the faculty in Granada? I know they were mystified by Ana's departure and remain highly curious if not otherwise preoccupied. As for the present, I have hinted in the past at the need for secularization of the languarge for a broader audience. I was once knee-deep in the research but as with any language it requires frequent use to retain.

 

[Lagoon Island Pearls]

Are you still in touch with the faculty in Granada? I know they were mystified by Ana's departure

We were ascended to the TEM lab for high resolution imagery of fixed specimens. Though ground breaking, there were limitation issues. Although we were able to observe modified e-cells, the fixer masked otherwise discernible properties. Namely hormones and some proteins. We then evolved into collection and transportation of live specimens which was not easy to accomplish. Transporting live shellfish has regulatory issues in both countries. Some of this was dispelled by being not food related, but issues with invasive species and abandoned packages arose.

Although Ana communicated and with and was supported by Dr. Checa, our research bypassed the normal process for presenting and entering the curriculum because of it's significance. Covid-19 changed everything. Since then I never reached out, nor did Dr. Checa so I assumed the program died on the vine with so many other studies. Even if either had, it would be difficult without a motivated, collaborative lab associate.

I'm bewildered too. She was brilliant, but never published an article or paper since. It was amazing how two misfits were so close to revealing the deepest, undiscovered secrets of pearl onset on a cellular level. Our conferences inspired questions and answers that few enjoy. The discoveries of nacreous micro-structures where none were expected were profound if not revolutionary. It did give rise to subsequent studies though, including one discussed here at P-G (which has done well for education), challenging the status quo of flawed terminology. That publication hit close to home because most of the species studied were from this coast. Had I been the author, I would not have done it any differently.

Despite retirement and old age, I'd revisit the study at the drop of a hat, but the pearling industry doesn't support research and education insomuch as a fraction of a decimal point of what it does on advertising, marketing and prestigious globetrotting. Likewise, the gems labs are stuck in a loop of inadequate and antiquated protocols too. I can't do it all, insomuch as the field work, but I digress. At the very least, put out the call. There's not much more I can do in the meantime other than what I'm already doing at my own volition. Most of it will probably go to the grave when I do.

 

[SteveM]

Despite retirement and old age, I'd revisit the study at the drop of a hat,

Age is only how we feel. I'm a relatively recent member of the club. Another retiree, Ken Scarratt (former director of GIA Bangkok) was intimately entwined in the Nautilus pearl controversy and might provide an opening to 'the establishment.' I know Blaire (GemGeek) remains in contact with him, perhaps a conversation could be initiated.

Most of it will probably go to the grave when I do.

This brings to mind my sleuthing in search of the loose Nautilus pearl described by and assumed to be in the possession of Arthur Willey, the grandfather of Nautilus research. With the help of Checa's connections at the London Malacological Society we scoured the specimen collections at Willey's various UK positions, from University College, Guy's Hospital, to Trinity College (Cambridge), At Cambridge we were told the only person who would have known where to find the pearl would have been the late G.P. Wells (son of H.G.), who was a colleague of Willey's in the Zoology Department. Willey went on to direct the Colombo Museum (Sri Lanka) and finally ended his career at McGill Univeristy in Montréal. I successfully contacted the Colombo Museum director and even wrote to a known Willey descendent in Montréal.

That pearl must still be in Willey's pocket!

 

[Lagoon Island Pearls]

Age is only how we feel. I'm a relatively recent member of the club. Another retiree, Ken Scarratt (former director of GIA Bangkok) was intimately entwined in the Nautilus pearl controversy and might provide an opening to 'the establishment.' I know Blaire (GemGeek) remains in contact with him, perhaps a conversation could be initiated.

Welcome to the club! I've got DISH, so my range of motion is radically decreasing. It's not painful insomuch a stiffening. Ken follows me on Facebook and I'm always flattered when he likes my pearl posts. I'd rather not impose upon a retired person directly, but perhaps posting the call there might stimulate a response.

That pearl must still be in Willey's pocket!

The families of an estate are often indifferent to the monetary or otherwise significant value of items within a collection. For that reason, I've been tagging my rarest pieces so they're not dismissed as just another pearl after I'm gone. Perhaps that's what happened? Are you aware of other portions of his collection in private hands than may be untagged?

 

[SteveM]

That is gracious to share your condition, hopefully pain remains a minor issue. Yes, why not post knowing Ken will likely see it?

I was single-tracked on the pearl, so no additional awareness. And have only assumed Willey retained it.