tains a fine pearl. Moreover,
like the bison and the wild pigeon, the pearl-bearing molluscs may be
greatly diminished in numbers or even exterminated by the greed of man
and his fearfully destructive methods of harvesting nature's
productions. In fact, the fisheries have been dwindling in yield for
some time, and most of the fine pearls that are marketed are _old_
pearls, already drilled, from the treasuries of Eastern potentates, who
have been forced by necessity to accept the high prices offered by the
West for part of their treasures. In India, pearls have long been
acceptable collateral for loans, and many fine gems have come on the
market after failure of the owners to repay such loans.

Having considered the factors bearing on the value of pearls, we will
next consider briefly their physical properties. The specific gravity is
less definite than with minerals and varies between 2.65 and 2.70. It
may be even higher for pink pearls.

PHYSICAL PROPERTIES. In hardness pearls also vary, ranging between 3-1/2
and 4 on Mohs's scale. They are thus very soft and easily worn or
scratched by hard usage. A case showing the rather rapid wearing away of
pearls recently came to the attention of the writer. A pendant in the
shape of a Latin cross had been made of round pearls which had been
drilled and strung on two slender gold rods to form the cross. The
pearls were free to rotate on the wires. After a period of some twenty
or more years of wear the pearls had all become distinctly cylindrical
in shape, the rubbing against the garments over which the pendant had
been worn having been sufficient to grind away the soft material to that
extent. The luster was still good, the pearls having virtually been
"peeled" very slowly by abrasion.

CARE OF PEARLS. This example suggests the great care that should be
taken by owners of fine pearls to prevent undue rubbing or wear of these
valuable but not extremely durable gems. They should be carefully wiped
after being worn to remove dust and then put away in a tightly closed
case.

Pearls should never be allowed to come in contact with any acid, not
even weak acids like lemonade, or punch or vinegar, as, being largely
calcium carbonate they are very easily acted upon by acids, and a mere
touch with an acid might ruin the surface luster. Being partly organic
in nature, pearls are not everlasting, but must eventually decay, as is
shown by the powdery condition of very old pearls that hav