relegate
a good many specimens of every mineral species to the semiprecious
class; thus a diamond that is dull in appearance, gray in color, and
only translucent (not transparent) could then not be classed as a
precious stone, for such a crystal would lack all beauty, and the
diamond is not the rarest of gem stones. Further, only certain
varieties of the mineral corundum and of beryl could be called
precious; the vast bulk of these minerals would be only semiprecious.
Color
can not furnish a satisfactory basis of division for, in addition to
corundum (ruby), many red minerals are used as gem stones, such as
spinel, garnet, opal, jasper, fluorite, and tourmaline; in addition to
sapphire, many blue minerals are used, such as benitoite, sodalite,
fluorite, turquoise, azurite; and many green minerals, such as
feldspar, fluorite, tourmaline, variscite, malachite, and hiddenite.
Absolute lack of color, characteristic of some diamonds, is also shown
by many other gem stones, such as quartz, beryl, phenacite, and topaz.
Luster
and transparency vary considerably, not only in the same mineral but
even in the same crystal. The presence of impurities or flaws may have
a marked effect on the luster of a mineral, so that two crystals of the
same mineral may exhibit very different degrees of luster and
transparency.
Hardness
can not be a deciding factor, unless it is said that all minerals must
have a hardness of 9 or more in order to rank as precious stones; but
this requirement would exclude emerald, which has a hardness ranging
from 7-1/2 to 8. If the limit is placed at 7-1/2 to 8 (that of
emerald), then chrysoberyl (8-1/2), topaz (8), phenacite (7-1/2 to 8),
and perhaps a few others like the minerals of the spinel group (7-1/2
to 8) would have to be included.
The
rarity of gem stones has often been set up as a criterion of their
value. It may be true that, in general, a very rare gem is of greater
value than an equally attractive but more abundant one, but the rarity
of a stone may be offset by its properties. The diamond is by many
people regarded as extremely rare, but in comparison with such gem
stones as benitoite, hiddenite, and many others it is very abundant.
The
foregoing statements are intended to show that gem stones can not
logically be classified as either precious or semiprecious and that
neither cost, beauty, hardness, nor rarity, whether considered
separately or together, can be made to serve as an exact basis of such
a classification. Of course, an arbitrary classification of gem stones
may be proposed, but it is not likely to be universally adopted,
especially if it ignores the particular properties, such as color and
hardness, that characterize gem stones in general.
PRODUCTION.
From
the beginning of this century to 1914 the value of the precious stones
annually produced in the United States has been about a third of a
million of dollars. The lowest value, $208,000, was reported in 1906;
the highest, $534,280, in 1909. During the first year of the war (1914)
the value of the production ($124,651) dropped to the lowest figure reported since 1896. There has been a steady increase since 1914 in the value of the precious stones pro-
