CHEMISTRY, PROPERTIES AND TESTS OF PRECIOUS STONES
What constitutes a precious stone is the question which, at the onset, rises in the mind, and this question, simple as it seems, is one by no means easy to answer, since what may be considered precious at one time, may cease to be so at another.
are, however, certain minerals which possess distinctive features in
their qualities of hardness, colour, transparency, refractability or
double refractability to light-beams, which qualities place them in an
entirely different class to the minerals of a metallic nature. These
particular and non-metallic minerals, therefore, because of their
comparative rarity, rise pre-eminently above other minerals, and become
actually " precious."
is, at the same time, but a comparative term, for it will readily be
understood that in the case of a sudden flooding of the market with one
class of stone, even if it