Mantle (t)issues

[Doos]

Hi all,

Most gemologists believe that the spaces inside non-nucleated freshwater pearls are caused by dissolvation of the foreign mantle tissue that was inserted in the mantle of the bivalve.
Thus the nacre was secreted around the mantle tissue irritant.

However lately I've been hearing that the opposite happens. The nacre is deposited inside the irritant tissue (which formed a sack) and gaps inside the formed pearl are probably caused by gasses.

Could some confirm either of the two ideas and maybe point me to good internet resources that might give me some more reading fun.

 

[Zeide Erskine]

Mantle (t)issue

Mantle (t)issue

Hi,

The mantle tissue implant forms the pearl sac. There is no mantle tissue remnant in tissue nucleated pearls be they freshwater or saltwater. There are some keshis, naturals, and freshwater cultured pearls that do have cavities. However these cavities have nothing to do with the nucleation process and may be due to metabolic or bacterial process in that particular pearl sac. There are various possibilites including unstable conchiolin that may disintegrate still in situ (while the pearl is growing) or later. Some freshwater cultured pearls are also nucleated with small wax beads of 1-2mm diameter that are melted out after drilling. Hollowing may also occur in bead nucleation. In that case there is a distinct separation between nacre deposit and bead nucleus. Many of such pearls get destroyed in the drilling process, others have the conchiolin destruction occur after drilling and become unstringable later. Does that help?.

Zeide G. Erskine

 

[Doos]

Thanks for the reply,

So I take it that the pearl grows within the mantle sack (the foreign one) and not from the bivalve trying to encapsule the foreign tissue.

Is that correct?
And if so, what is irritating the foreign tissue that triggers it to deposit conchiolin/nacre?

This has been puzzling me for some time now.