Mystery Pearl?

[SteveM]

Attribution: The Journal of Gemmology / 2010 / Vol. 32
Researcher, author and photographer: Thomas Hainschwang, Director, GemLab(Liechtenstein).

This is not a shell, and it is not a fossil. It is, however, an 84.77-carat natural porcelaneous saltwater object composed of aragonite. This object, and others like it, were offered by local sources to a prominent European pearl collector as natural pearls.

Will allow for comments?

 

[Seabourn Pearls]

I'm wondering if, instead of a shell fragment, an entire shell became stuck inside a non-nacreous mollusk thus initiating the processes of pearl creation.

 

[SteveM]

Should have mentioned that it's solid aragonite, no significant core or nucleus.

 

[Lagoon Island Pearls]

Should have mentioned that it's solid aragonite, no significant core or nucleus.

The outside surface of the object is smooth, mirroring the internal nacreous lining of a gastropod's shell.

My guess would be, it's plausible, the pearl sac formed internally (opposed to externally as we know it), as a coincidental graft from the snail's epithelial cells.

Once the host animal matured and died, the original shell had fallen away, leaving a "cast" impression.

Although not a geological in nature, it could possibly be described as a biological fossil.

 

[SteveM]

Once the host animal matured and died, the original shell had fallen away, leaving a "cast" impression.

This is on the right track.

Although not geological in nature, it could possibly be described as a biological fossil.

Not fossil (carbon dating was among the tests, in any case aragonite normally degrades to calcium carbonate during fossilization), though I understand your meaning to be 'fossil-like.'

 

[Lagoon Island Pearls]

This is on the right track.

Not fossil (carbon dating was among the tests, in any case aragonite normally degrades to calcium carbonate during fossilization), though I understand your meaning to be 'fossil-like.'

I can't help but wonder whether or not this was xenogenetic in it's formation, namely which species acted as host. Had the finders concluded the donor species?

 

[SteveM]

Had the finders concluded the donor species?

Hainschwang did reach a definitive conclusion. Will post late this evening Pacific time in case anyone else cares to comment without prejudice in the interim.

 

[Marianne]

This is better than the last Jance mystery!
Waiting.......
Marianne

 

[pattye]

(Plus it's really cute! I can just see it dangling from a charm bracelet---------lol.) Please forgive me, Steve.

 

[GemGeek]

My first thought was a pseudomorph after the original, which had dissolved. This is mindbending - a pearl shaped like a trochus. My brain hurts!

 

[SteveM]

(Plus it's really cute! I can just see it dangling from a charm bracelet---------lol.) Please forgive me, Steve.

Pattye, I'll just assume you're dissimulating an overwhelming curiosity. But yes, perfect charm material!

Guess it's time.

After determination of natural aragonite composition and an age less than 500 years, there was nothing left for Hainschwang to do but call in a top malacologist, who declared the species to be Magilus Antiquus—the Burrowing Coral Snail. First photo below is of a fresh shell.

M. Antiquus grows a long neck, either as it burrows into brain coral as its common name suggests or as the living coral grows around it (Hainschwang adopting the latter version) in order to retain access to the surface for feeding purposes. The mollusk resides at the end of the neck at the coral surface, having abandoned its entombed, coiled chamber.

Hainschwang's conclusion is that as biomineralization of the neck proceeds, biomineral material drains into the coils and crystallizes, in the present case eventually filling the void.

But fossils of Magilus Antiquus are well known. They also are white, porcelaneous and solid (great fossil shot below illustrating Western Pacific coral habitat). I would certainly be interested to see similar analytical procedures performed on analogous fossils in order to compare with Hainschwang's findings in the Journal of Gemmology article (link to abstract).

 

[Lagoon Island Pearls]

You learn something every day.

Kind of reminds me of a cross between a toredo (boring worm) and a geoduck (long necked clam).

Thanks for posting this, Steve.

 

[GemGeek]

Being composed of aragonite doesn't make it a pearl. It is a form of pseudomorph (bio-mineralization) after the original mollusk. Technically, a pearl must be created by a living mollusk and this one was long gone. Or am I just being cranky?

 

[SteveM]

Being composed of aragonite doesn't make it a pearl. It is a form of pseudomorph (bio-mineralization) after the original mollusk. Technically, a pearl must be created by a living mollusk and this one was long gone. Or am I just being cranky?

The paper did conclude that it was produced by a living mollusk, although certainly not in a pearl sac.

Structure of the 'object' includes classic crossed-lamellar flame (below) and, at least in some areas, concentric layers.

In conclusion the paper poses the question of whether the object would be best called a pearl or 'calcareous concretion', a term that has been alternatively applied to conventional non-nacreous pearls as well. 'Calcareous concretion' was the preference in this case.

 

[DrTKStern]

All,

We see a lot of these objects in North Borneo/Celebes area, and everyone refers to them as "fossil pearls" of no value. Some are so soft they can be marked by one's fingernail, which I recollect means a hardness of 2 or less on Moh's scale. Interesting to see the "flame" structures. Another great contribution by Steve.

Tom

 

[SteveM]

We see a lot of these objects in North Borneo/Celebes area, and everyone refers to them as "fossil pearls" of no value. Some are so soft they can be marked by one's fingernail, which I recollect means a hardness of 2 or less on Moh's scale.

Tom, thanks. Magilus fossils are quite common as you say, so the continuing enigma here is that this object did not test as a fossil (aragonite composition, plus C14 dating). In the case of the actual fossils where the aragonite would have decayed to calcium carbonate, the hardness would indeed be low.

 

[GemGeek]

Okay, now that I have read Thomas's article, I see that the creature filled its own shell as it grew upward with the coral. I wonder at all the incredible things that nature innocently goes about, of which we have no clue. Truly amazing and resourceful behavior.

I think that the powers that be will call it a calcareous concretion, as they don't really like calling non-nacreous pearls by the name of pearls right now.

I wouldn't mind having a nice little pendant!

 

[SteveM]

I think that the powers that be…don't really like calling non-nacreous pearls by the name of pearls…

The arguments in favor:

Hubert Bari in Pearls:

Here it is necessary to demolish an idea that is frequently encountered on websites and in books: the claim that only nacreous pearls should be called 'pearls', while the others should be regarded as no more than 'concretions.' All the concretions produced by molluscs with shells are pearls, whether they are nacreous or not. They all have the same composition and are formed in the same way. Only the external appearance and the manner in which they react to light are different, which is not enough to justify differentiating one kind from another in the nomenclature. In fact, the GIA has recently placed a ban on the differentiation between (nacreous) pearls and (non-nacreous) concretions. When you see the splendour of a Melo pearl, it is obvious that this distinction promoted by the lobbies of dealers in nacreous pearls is wholly unwarranted.

As added evidence for the advent of a 'non-nacreous' pearl era, Elisabeth Strack, according to the program notes for her presentation at the AGA Conference on February 02 in Tucson, will 'include comments on the rise of the Non-Nacreous Pearls.'

As nacreous pearls become ever more perfect and predictable (and ubiquitous), it's only 'natural' that there would be an increasing interest in the alternatives.

 

[DrTKStern]

The arguments in favor:

Hubert Bari in Pearls:



As added evidence for the advent of a 'non-nacreous' pearl era, Elisabeth Strack, according to the program notes for her presentation at the AGA Conference on February 02 in Tucson, will 'include comments on the rise of the Non-Nacreous Pearls.'

As nacreous pearls become ever more perfect and predictable (and ubiquitous), it's only 'natural' that there would be an increasing interest in the alternatives.

CIBJO issued a definitive statement some years ago that non-nacreous indeed are pearls.

Tom

 

[GemGeek]

That is the way it should be, thanks.