Ross Mayhew asks, "Can any one tell me why the Japanese pearl industry does not just use some other material except fresh-water clams, many of which are endangered spp now because their habitat is nearly destroyed?? Surely there are other materials just as good - natural or synthetic?" Commercial collecting of mussels is regulated on a state-by-state basis, and, at least in legal theory, the collectors harvest only from the common species. It is illegal to collect endangered species for commercial purposes, of course. The Japanese use American freshwater shells for pearl nuclei because molluscan diseases are unlikely to be transmitted from fresh water to salt water. Pearl oysters are prone to fungal and other diseases, apparently. Unsurprisingly, aragonitic molluscan shell makes a good base for depositing aragonitic mother-of-pearl. I have no doubt that the Japanese have tested many substances for this purpose, including artificial ones, and have achieved the most efficient results this way. Freshwater musselshell cannot be the most convenient substance for them to use, but it's probably the best. Andrew K. Rindsberg Geological Survey of Alabama