judging by the rings on the pearls outer nacre - they would be described as circled or ringed pearls. The rings form as a result of pressure to the pearl as it is developing within the oyster. When were they purchased? Have you tried the tooth test yet? Information on the tooth test can be found on the page dedicated to identifying cultured pearls.
The Chinese production of Chinese Freshwater Cultured Pearls that looked like the breakfast cereal - Rice-Krispies sky-rocketed in the 1980's reaching approximately 80 tonnes!
But it wasn't until 1995, that Chinese Freshwater Cultured Pearls made their major debut at the JCK Vegas trade show. Estimates of Chinese FWCP production ran as high as 500 tonnes that year and DOUBLED again by 1997 (Strack, 2006).
Although the culturing of 7-8 mm pearls could take from 5 -7 years the sheer volume that could be produced from a single mussel meant that the quantities of such pearls would remain high.
What have they been strung on if you don't mind me asking Min?
I can't see any knots between the pearls? If knots are made frequently between the pearls, there is less danger of losing them should the thread break, as only one or two will fall off. The longer the pearl necklace the more important as you could imagine, the knotting is between the pearls.
