COLOR OF GEMS
The
color of gems is one of the most essential features of their value.
While certain colorless gems, such as the diamond, are highly prized,
even the diamond would lose much of its value if it did not flash
colored lights. So the quality of affording a permanent color probably
leads to much of the esteem in which gems are held. The colors of the
rose and the violet are not less pleasing than those of the ruby and
amethyst, but the former endure but for a day while the latter can be
handed down unimpaired from generation to generation. It was probably
to secure varieties of color that the ancients first used gems, for
their classifications and designations of precious stones were based
chiefly upon this property. With them almost any green stone was known
as emerald, blue as sapphire, and red as ruby or carnelian. This fact
makes it difficult in reading accounts of gems as given by ancient
authors to know what mineral is meant. Distinctions of hardness and
specific gravity, now so much in use, seem to have been ignored by them
for the most part. With the grouping of minerals according to their
chemical composition, the significance of color largely disappeared as
a means of distinction, since individual specimens of the same
composition, and hence the same species, may vary greatly in color.
Usually the quantity of ingredient required to produce a certain color
is too small to be detected by chemical analysis. That the custom of
distinguishing gems by their colors still survives, however, to a
considerable extent, is evidenced by the fact that different names are
still applied to gems of the same mineral when of different colors.
Thus sapphire and ruby are both corundum; and emerald and aquamarine
are beryl. The mineral quartz appears in a multitude of colors, to
nearly all of which different names are given. Hence gems of two
different names may occur even in the same crystal: as in a piece of
quartz, from one portion an amethyst may be cut and from another a
citrine. On the other hand, different species may present stones of
exactly the same color. Thus corundum, spinel and garnet all afford red
stones, often nearly alike in tint; or emerald and tourmaline both
give green stones. Speaking from the mineralogical standpoint, there
are few minerals and fewer gems in which color is a constant and
essential property. Those which may be mentioned as belonging to
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