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mately
bring a price much beyond that of the labor of cutting, which is at
present from a dollar and a half to two dollars a dozen for stones of
the ordinary sizes. Considerable rock crystal is used for making the
so-called "pebble" eye-glasses and spectacles. It is a common notion
that these are more beneficial to the eyes than glass. There seems to
be no good reason for this opinion, however, and unless the crystal is
cut in a certain definite crystallographic direction, that is, at right
angles to the prism, the light coming through to the eye of the wearer
will be broken up by double refraction, and may be positively harmful
in its effects.
Another
occasional use to which rock crystal is put is for making mirrors, for
which purpose it is said to be superior to glass in that it does not
detract from the rosiness of the complexion.
The
chief source of the rock crystal used in the arts at the present time
is Brazil. In several provinces of that country, but especially those
of Minas Geraes and Goyaz, large, clear masses, often in the form of
crystals, are found loose in the soil. These are picked up and shipped
to various markets, furnishing a supply of excellent material at small
cost. In India considerable rock crystal is obtained from localities in
the government of Madras, and fashioned by the natives into various
objects.
The
French and Swiss Alps, which probably furnished the raw material to
the Romans, still afford a small supply, of which limited use is made.
Quartz pebbles, derived doubtless from these Alpine sources, are found
in the bed of the Rhine and its tributaries, and it was to these when
cut that the name of rhinestones was originally applied.
The
Island of Madagascar has since the middle of the seventeenth century
been noted for the large masses of clear quartz to be obtained there.
The quartz is found mostly in stream beds in the form of rolled masses,
but also occurs in crystals. Single pieces are found weighing several
hundred pounds. The Madagascar quartz furnishes the material for most
of the crystal balls sold as Japanese, many of these being not even cut
in Japan. In our own country several localities afford clear quartz
crystals, the best known being Hot Springs, Arkansas, and Little Falls,
New York. Those from the latter locality are doubly terminated, and are
sold quite extensively in their natural shape for jewels, as they are
small and brilliant.
The
ancients prized rock crystal much more highly than we do, because it
answered them many of the purposes for which we now find glass cheaper
and more suitable. Wine-glasses were made from it, though at great
cost, a thousand dollars being considered a small price for one. Lenses
of rock crystal were used to concentrate the
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