Tom Stern's natural pearls

There was a challenge that certain pearls could not be nautilus, because they had flame patterns and nautilus are nacreous. It just made me wonder why some tridacna pearls have a flame and some don't. There certainly is no flame in any clam shell I know of- or is there?
The Nautilus dilemma remains acute. While GIA might defend its certificates based on known anomalies in other nacreous mollusks such as Pinctada, practically every putative Nautilus pearl in history has been of the non-nacreous variety. Very difficult to explain, although heaven knows I have tried to find the answer.

Certainly the huge majority of Tridacna pearls are ugly lumps of ceramic, the shells being grossly constructed using pure mass to create the requisite strength. It is thought that relatively smaller species (such as T. Squamosa) offer finer shell features, and also that while within the pearl sac the aragonite platelet formation retains more organization?as long as the pearl is discovered before it attaches to the shell and stops rotating. (The absolute pride of my collection is a beautiful 53-carat drop that had become attached to the shell but was fortunately discovered prior to its degeneration into a baby Pearl of Allah.)

Species ID will get a boost as DNA techniques recently developed for fossil eggshells and bones have become accessible to the pearl labs. Until now, extraction of endogenous (native to the mollusk) DNA from shell material was not considered viable. This will be the source of my next news at the Nautilus thread, assuming there is news to report.
Dr Stern,
The Chau/Chav/Chow system is very common in the Natural Pearl trade for centuries.
This is the calculation..... carat X carat X 88 divided by 135 equals to 1 pearl chau/chav/chow.