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