Rice Krispies! These are Chinese cultured freshwater pearls, the earlier ones before they learned how to culture rounder ones. The mussels were nucleated with a small bit of mantle tissue.
Although they don't have much commercial value, I think they are a cool part of pearling history. I'm keeping mine!
One interesting thing is that I sometimes see imitation rice krispies. They did have value, in their time-- enough that some imitated them. My bracelet had a 14k gold clasp and 14K gold ball spacers. It's funny when you think of it. Now the pearls have little value but the price of gold has soared. How things change!