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intrinsic
value. It is not likely that any great excess or diminution of supply
will occur to change the value of the leading gems, such as diamond,
ruby, sapphire, and emerald, as they seem to be distributed in the
earth's crust in but sparing amount. Among the less valuable gems,
great variations in value have occurred, and may again. Thus the price
of precious opal has steadily declined since the discovery of the
Australian fields, although as fine gems are produced there as were
ever known. Topaz and amethyst have suffered a similar decline in
value, while the price of the gem known as " tiger eye" fell in a few
years from five dollars a carat to twenty-five cents a pound.
The
elements entering into the chemical composition of gems are not as a
rule themselves rare. They are chiefly silicon, aluminum, magnesium,
and other common elements, usually combined with oxygen, and all
abundant constituents of the earth's crust. It is thus not the rarity
of their elements which gives gems their high value, but rather their
peculiar properties as compounds.
Since
gems are unequal in value among themselves, many authorities
distinguish between gems and precious stones, and also subdivide the
latter into precious and semi-precious. To the class of gems belong,
according to such a classification, such stones as the diamond, ruby,
sapphire, and emerald; the precious stones include amethyst, rock
crystal, garnet, topaz, turquois, moonstone, opal, and the like; and
the semi - precious, jasper, agate, carnelian, lapis lazuli, amazon
stone, labradorite, etc' Since the different kinds and qualities grade
into each other, insensibly however, and no sharp lines can be drawn,
the distinction hardly seems worth making. In. the following pages,
therefore, the terms gem and precious stone will be used
interchangeably, and will be considered to include any mineral, and
even some substances of animal and vegetable origin, which have
attained a certain vogue for purposes of ornament.
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