The
character of the matrix is also in a great measure the cause of the
variety of the stone, for it is obvious that the same salt-charged
aqueous solution which undergoes change in and on ironstone would
result in an entirely different product from that resting on or
embedded in silica.
Following
out the explanation of the aqueous solution, in which the earth-crust
constituents are secreted, we find that the rarer and more precious
metals do not generally enter into the composition of precious
stones—which fact may advisedly be repeated. It is, of course, to be
expected that beryllium will be found in the emerald, since it is
under the species beryl, and zirconium in zircon : but such instances
are the exception, and we may well wonder at the actions of the
infinite powers of nature, when we reflect that the rarest, costliest
and most beautiful of all precious stones are the simplest in their
constituents.
Thus
we find the diamond standing unique amongst all gems in being composed
of one element only—carbon —being pure crystallised carbon : a
different form from graphite, it is true, but, nevertheless, pure
carbon and nothing else. Therefore, from its chemical, as well as from
its commercial aspect, the diamond stands alone as the most important
of gems.
The
next in simplicity, whilst being the most costly of all, is the ruby,
and with this may be classed the blue sapphire, seeing that their
chemical constituents are exactly the same, the difference being one
of colour only. These have two elements, oxygen and aluminium, which
important constituents appear also in other stones, but
