Sapphires,
and Corundum, we might briefly consider one or two experiments carried
out upon the preparation of Zircons, Emeralds and Turquois, these
stones being the only others successfully reproduced in the laboratory.
By
the action of gaseous silicon fluoride upon zirconia (zirconium oxide),
crystals of Zircon (silicate of .zirconium) were formed. Experiments of
this nature are somewhat dangerous to do, as fluorine compounds,
especially if gaseous, are very deadly, and will attack almost
anything. The acid used for etching glass if it comes in contact with
the skin produces painful sores. Substituting beryllium oxide for
zirconia in the above experiment, hexagonal plates similar in hardness
to the Emerald were obtained. None of these methods are, however, of
commercial importance.
The
Turquoise, owing to its amorphous nature and opacity, has, besides many
forms of imitation and substitutes, such as Malachite, Bone Turquoise
or Odontolite, etc., been so successfully prepared artificially that
without destroying the stone it is difficult to distinguish between the
natural and the laboratory production. They are as a rule mixed up with
parcels of natural stones in the rough, and are in many cases much
finer than the real Turquoise. To make their appearance more natural,
they are stained with Limonite (hydrous oxide of iron), and their
detection as a consequence is somewhat difficult. It is stated by Dr.
Max Bauer, in his admirable book on " Precious Stones,"1
that if these stones are put into water they darken in colour, and
minute cracks may be seen on the surface if examined with a lens. The
only
