THE PEARL
composition,
are not nacreous. Occasionally, however, the term is still applied
specifically to pearls from the Indian Seas, though their "orient" or
luster is not always finer than that of like pearls found in many other
localities.
Pearl
oysters are varieties of the Avicula Margaritifera, of which the
Meleagrina Margari-tifera is the most prolific of mother-of-pearl and
pearls combined, and, the Indian excepted, yields the finest pearls.
All pearl oysters do not produce sufficient mother-of-pearl to make
their shells valuable, nor do they all contain pearls. The name
therefore applies to all oysters whose secretions are productive, in
some degree, of mother-of-pearl and therefore under favorable
conditions of pearls also.
"Fresh-water"
or "sweet-water" pearls are, as the name signifies, those found in the
mol-lusks of inland waters. This mollusk is a mussel. The name "mussel"
in Anglo-Saxon signifies something which retires on being touched. It
is known as " Unio " of which there are many pearl-bearing varieties.
In both the sea oyster and the fresh-water mussel, other nacreous formations occur of
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