It's a blister pearl. What other kinds of pearls do you have sir? I am looking at promoting in the near future, natural pearls and pearls of interest on this site.
Your sincerely Yvonne
Large pearl by: Anonymous
It is no big/large pearl. I have more large pearls
When a growing pearl is very near to the nacreous lining of the shell, the pressure between the two hard surfaces results in a rupture of the pearl-forming sac and layer of the shell, and becomes attached to the shell, and the under portion is prevented from growing further. the upper or exposed surface receives other layers, resulting in a "bouton".
As the shell around the pearl continues to grow, it gradually closes out and almost totally conceals the pearl. Since it is constantly wasting away on the exterior surface as it grows on the interior, it follows that in time the shell passes the pearl quite through to the outside, where it rapidly decays. Meaning the oyster forces the intruder directly through the wall of its house instead of by way of the open door, and magically closes the breach with its marvelous masonry.
Embedded pearls like this are generally of diminshed luster.
