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PRECIOUS STONES.
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Moose Mountain, in New Hampshire, may be cited as a locality.
The
so-called " Bristol Diamonds " belong to this variety of Quartz, and so
does the "Brazilian pebble." Lake George, in New York, has also given
its name to " Lake George Diamonds." Many other localities have also
had their names used in this way. Speaking generally, when Bock Crystal
is cut to simulate Diamond, the word " occidental " is prefixed. The
real nature of the mineral may be recognised by its lower specific
gravity than other colourless precious stones, by its hardness being
exactly 7, and by its want of fire. From Diamond and colourless Spinel
it differs in being doubly refracting.
The
applications of this variety in the Arts are numerous. As Quartz sand
it enters largely into the composition of better qualities of glass,
and now pure fused Quartz is being used for some special purposes where
glass was used previously. The fashionable ladies of ancient Borne used
it to cool their delicate hands with, for this purpose carrying small
spheres of Bock Crystal in hot weather. Pliny was informed that a ball
of it formed the best means of cauterising any part of the body by
physicians, the patient being placed in sunshine for this operation,
and the rays passing through the sphere brought to a focus at the
desired point. King ("Precious Stones") amongst a wealth of other
illustrations of its use in past times quotes an amusing dialogue in
Aristophanes in which the use is suggested of a Crystal sphere to
conveniently dispose of an unwelcome writ. The use of " Brazilian
pebble " in the manufacture of spectacle lenses has long been known.
Bock Crystal is also used in lamps for some forms of light treatment in
medicine. Fine
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