mother-of-pearl or nacre nā´kər [key], the iridescent substance that forms the lining of the shells of some fresh-water and some salt-water mollusks. Like the pearl it is a secretion of the mantle, composed of alternate layers of calcium carbonate and conchiolin. Among the chief sources are the pearl oyster, found in warm and tropical seas, chiefly in Asia freshwater pearl mussels, which live in many rivers of the United States, Europe, and Asia and the abalone of California, Japan, and other Pacific regions.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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