THE ORIGIN OF PRECIOUS STONES.
Though the origin, formation, composition, characterÂistics and tests of each stone will be examined in detail when dealing with the stones seriatim, it is necessary to enquire into those particulars of origin which are common to all, in order thoroughly to understand why they differ from other non-metallic and metallic minerals.
At
the very commencement we are faced with a subÂject on which
mineralogists and geologists are by no means in full agreement, and
there seems just ground for considerable divergence of opinion,
according to the line of argument taken. It is a most remarkable fact
that, precious as are certain stones, they do not (with a few
exceptions) contain any of the rarer metals, such as platinum, gold,
etc., or any of their compounds, but are composed entirely of the
common elements and their derivatives, especially of those elements
contained in the upper crust of the earth, and this notwithstanding the
fact that gems are often found deep down in the earth. This is very
significant, and points to the conclusion that these stones were formed
by the slow percolation of water from the surface through the deeper
parts of the earth, carrying with it, in solution or suspension, the
chemical constituents of the earth's upper crust; time and long-
