CHAPTER XII.
IMITATIONS, AND SOME OF THE TESTS, OF PRECIOUS STONES.
We now
arrive at the point where it is necessary to discuss the manufacture
and re-formation of precious stones, and also to consider a few of the
tests which may be applied to all stones. These are given here
in order to save heedless repetition : the tests which are specially
applicable to individual stones will more properly be found under the
description of the stone referred to, so that the present chapter will
be devoted chiefly to generalities.
With
regard to diamonds, the manufacture of these has not as yet been very
successful. As will be seen on reference to Chapter II., on '' the
Origin of Precious Stones," it is generally admitted that these
beautiful and valuable minerals are caused by chemically-charged water
and occasionally, though not always, high temperature, but invariably
beautified and brought to the condition in which they are obtained by
the action of weight and pressure, extending unliroken through perhaps
ages of time.
In these circumstances, science, though able to give
