I received a string of pearls in to value which were sold as South Sea pearls at a price of R200000 (GBP11000). They are a 'fat donut' shape 10:50 - 11:00mm in diameter. I couldn't see the nacre down the drill hole so had them X-rayed. The result was inconclusive. I took it a step further and had a pearl CT scanned. You can see the result in the picture. I believe one can get non-nucleated and nucleated South Sea pearls. It appears that the only test left is to check the Mg content to determine whether salt or freshwater.