OCCURRENCE OF GEMS
It
was the opinion of the ancients that gems were largely confined in
their occurrence to tropical countries. Most gems which they knew were
so obtained, India being the chief source of them. Their wise men
reasoned, therefore, that the warmth and light of the sun of the
tropical zone were needed to give gems that fire and brilliancy which
made them precious among stones. With the wider knowledge of the earth
which has been gained in later times, however, it has become evident
that climatic conditions have little or nothing to do with the
occurrence of gems. The greater oxidation produced by the heat of the
sun in the tropics may add to the warmth of color of such stones as the
carnelian and agate, but it would have a tendency to fade the amethyst
and sapphire. A greater abundance of gems in the tropics may arise from
more extensive decomposition of the rocks there, and this is
undoubtedly a favorable circumstance. Moreover, glaciated countries,
such as the northeastern portion of North America, have a soil composed
of too heterogeneous a mixture to favor the search for gems. So far as
the underlying rock is concerned, however, there is not, so far as we
know at present, any distribution by latitudes which favors one
locality over another. Hence the mountain fastnesses of the Urals
furnish gems no less than the broad valleys of India, the bleak shores
of Labrador as well as the steaming jungles of Burmah, and the barren
veldt of the Transvaal as well as the thickly settled valleys of
Bohemia.
The
first discovery of gems in a region is usually made, like that of gold,
in the beds of streams. Often it is in the search for gold that gems
are found, as is illustrated by the fact that the discoveries of
diamonds in Brazil, sapphires in Montana, and rubies in North Carolina
were made in this manner.
The
frequent occurrence of gems in the beds of streams is due to the fact
that the gem minerals are usually harder and less easily decomposed
than the other minerals of the rocks in which they were formed. Hence
they remain after the mother rock has disintegrated and its
constituents for the most part removed. The discovery of gems in a
stream bed is further facilitated by the enhancing of their color when
wet,
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