This book has everything that one would want to know about pearls. It includes the pearl's cultural and natural history, commerce, industrial and medical uses, methods of pearl gathering, lists of famous pearls, ancient legends about pearls, (black and white) pictures of pearls, and portraits of royalty with their pearls.
Since this book was written in 1906, the values of pearls are outdated, and the pre-metric measurements used are confusing.
This is the best and most useful resource on pearls that I have discovered.