Hastings' Dictionary of the Bible (1898)
PEARL. The best pearls are produced by a shell-fish of the oyster species, though they are found in other mollusks. The pearl-oysters grow in clusters on rocks (hence called "pearlbanks") in the Persian Gulf, on the western coast of Ceylon, on the coasts of Java, Sumatra, etc., and in some parts of Europe. The shells are obtained by diving, and this is done by a class of persons trained to the business. The Ceylon pearl-fishery bank is about 15 miles from the shore, and 72 feet deep on an average. The fishery begins in April, when the sea is most calm, and continues five or six weeks.
One shell contains from eight to twelve pearls. The largest are of the size of a walnut, but they are rarely as large as a cherry-stone. " A single pearl has been valued at $350,000. Pearls were anciently, as now, used in the East as personal ornaments. 1 Tim 2:9; Rev 17:4; Rev 18:12-16. , it was evidently regarded as among the most precious substances, and, compared with gems, it was esteemed as more valuable than at present. Matt 7:6; Matt 13:45-46; Rev 21:21.