MODES OF ORIGIN.
The origin
of each gem will be dealt with in its proper place, but here again a
few general points may be noticed. It is well worth the reader's while
to study such a book as that of Robert Boyle's above referred to, to
gain an insight into the earnest endeavours these old scientists made
to discover the how, why, and wherefore of Nature's working. Aristotle
in the third book of Meteors states bis belief that the infusible
stones were made by a " dry exhalation " ; another theory was that they
were formed of a mixture of earth and water congealed by cold ; later
again the almost universal belief was that they originated from the
actual fusion by heat of various earthy matters. Boyle, by careful "
examens " of different chemical substances, as alum, salt, saltpetre,
etc., in the process of crystallisation, came to the conclusion that
all gems originated from crystallisation from a watery solution ; he
came to the conclusion that for the particles, of which the mineral was
composed, to be able to move into their proper places so as to
unerringly build up a crystal of a definite geometrical form, these
particles must have existed in a fluid state of some sort. Crystals are
formed either by sublimation, solidification from a molten mass, or
separation from a solution, and it is quite possible one of the
commonest ways of formation of the crystals of mineral substances is by
separation from
