Pearl Symmetry and Rotation Mechanics

[SteveM]

Round, Drop, Button, Circle.

Symmetry in pearls is the foundation of their appreciation and historical value. So much so that the cultured pearl industry went to great extremes to give them a head start and helping hand with round bead nuclei. But even with the head start the mollusk must deposit its shell material in a regular and consistent manner.

Rotation within the pearl sac creates the conditions for symmetry. In a respected 2013 paper by three prominent European researchers with personal connections to Pearl-Guide (free PDF download), the mechanism for nacreous pearls was theorized mathematically as a “ratchet effect” resulting from the orientation of nacre platelet growth fronts as each new layer of nacre is deposited. Here is their hydrodynamic formula (read the paper for logic!!!):

U = τ (r3-a3)/( 8 μ π r3 a3) ≈ 3 τ ε /( 8 μ π a) ​

The paper has many illustrations, utilizing pearls provided by Douglas. I was privileged to spend many hours with all three researchers on the University of Granada campus in front of an electron microscope exploring these and other pearl microstructure issues.

As the paper is from 2013, updates or related research would be welcome.

Alas, this research applies only to natural and cultured nacreous pearls. It does not address the origin of symmetry in porcelaneous pearls such as the white pearls from bivalve or gastropod shells in THIS P-G thread, or the more famous and colorful pearls from gastropods such as Cassis Cornuta, Melo-Melo and Strombus Gigas (conch) among many others.

And finally, extensive electron microsope and literature review towards discovering the origin and formation of the symmetrical pearls below have frustrated all attempts at understanding. The growth pattern is as if someone stuck their fist in a bowl of spaghetti and gave it a quarter-turn. The shell material is strangely translucent, mollusk origin unknown. From the pattern of the vortex it is clear the same mathematical formula is at work that produced the famous unnamed hurricane ‘The Perfect Storm’ in late October of 1991 (see photo comparison).

Looking forward to further enlightenment. We could be here for quite some time!

 

[SteveM]

This thread was brought to the attention of the University of Granada faculty and the associated international biomineralization research team. It has reawakened interest in studying the nature of those pearls with vortical growth patterns, and to readdress the rotational mechanics involving all non-nacreous pearls. With updated technology and access to samples, there is hope for progress.

The team is ceaseless in its groundbreaking research on biomineralization and its underlying crytsallography. Recent papers focus on helices (vs. vortices), specifically in the shells of pteropods (small gastropods serving primarily as part of the plankton biomass). THIS ONE personally stood out for its use of fusilli lunghi as illustration (including cooking instructions!).

Did anyone think "fist in a bowl of spaghetti" was not proper science lingo?

 

[CortezPearls]

I just read the article and it oddly took me back to my school years studying Biochemistry, the structure of proteins -including amiloids- and all the pasta I was eating (and not much else!).
Boy it's complicated! Shell formation via biomineralization is truly complicated and there are so many pathways to making shell, as if Nature said: If I'm going to build shells...let's just make them all different and play around!
Nature is amazing.