The object which I have proposed to myself in these two lectures is to
consider, not the history nor the artistic interest of precious
stones, but simply some of their curious properties. In the first
place, then, I will ask you to accompany me in the inquiry as to those
characters of precious stones to which they owe their beauty and their
value, and next to pursue the inquiry a little farther and to see how,
by means of these characters, the same stones may be studied, and
hence, also, identified with accuracy.
From the earliest times certain minerals, which are conspicuous for
their beauty, have been prized for decorative purposes; the brilliant
green hue of malachite, the deep blue of lapis lazuli and the rich
color of red jasper would naturally attract early attention. But these
particular minerals are not numbered among the true precious stones;
they do not possess the remarkable qualities which endow the diamond,
the ruby or the topaz with their peculiar attractiveness. The two
essential qualities, namely, brilliancy and hardness, are only
possessed by certain rare minerals; a brilliancy which makes them
unrivaled for ornamental purposes and a hardness which protects them
from wear and tear and makes them practically indestructible.
It is difficult in a town like London, where every jeweler's shop is
ablaze with diamonds, to realize that large and good stones possessing
these qualities are so rare; that thousands of natives are toiling in
the river beds of India, Burma and Ceylon washing out from the gravel
or the sand the little blue and red pebbles which are to be converted
by the lapidary's art into brilliant jewels of sapphire and ruby. Even
in that wonderful pit at Kimberley, where half the diamonds of the
world seem to have been crowded together for the use of man, although,
perhaps, ten tons of diamonds, worth more than £50,000,000, have been
extracted in twenty-five years, yet those which weigh more than an
ounce each may be counted on the fingers.
It is in the qualities of hardness and brilliancy that such minerals
as malachite and lapis lazuli fail; owing to their comparative
softness, they would not, if cut and polished, possess the sharp edges
and brilliant surface of the emerald or sapphire, and would soon
become dull and rounded by friction, even by the friction of ordinary
dust. Again, since they are opaque, they can never flash like the
sapphire or the emerald; and yet it is quite a mistake to suppose that
the necessary qualities are confined to those few stones which are
familiar to everyone, such as the diamond, ruby, sapphire, emerald,
garnet and amethyst. There are many others, though they are not so
well known. I think we may fairly assert that such minerals as
tourmaline, jargoon, peridote, spinel and chrysoberyl, though their
names may be familiar, are not stones which would be recognized by any
but those who are in some sense experts; while other minerals, such as
sphene, andalusite, axinite, idocrase and diopside, are possibly
almost unknown to most people, even by reputation. Yet all these
minerals possess qualities of transparency, hardness and beauty of
color which render them extraordinarily interesting and attractive as
precious stones. (A number of faceted stones cut from the less known
minerals were thrown upon the screen by reflected light.)
Take first the hardness. A few years ago the hardness of stones was a
very important character in the eyes of the mineralogist; it was one
of the characters by which they were invariably identified, and a
distinguished German mineralogist drew up a table by means of which
the hardness of minerals can be compared. Any stone is said to be
harder than the minerals of this scale which it can scratch, and
softer than those by which it can be scratched. In the right hand
column the gem stones are arranged according to their hardness.