Hi msLondon,

There is a whole thread already on this I will see if I can find it--it was a LOoooNNNg discussion----------under natural pearls, there is a thread near the top called "Maybe the oyster likes it"

Possibly, is how I would answer this--because most perfect rounds are going to be bead nucleated, whereas the tissue nucleated will be baroque or perhaps less round, but lots more nacre. It is easier to determine something like this, generally speaking, when comparing specific items, 2 pearls, 2 strands, etc.