144 A POPULAR TREATISE ON GEMS
excess
sufficient oxygen for forming silicic acid. A mixture of chalk or
magnesia, for instance, to the chloride of sili-cium, produced crystals
of diopside, perfectly colorless, with a characteristic slope of this
mineral. He also obtained crystallized felspar by the mixture of 1
equivalent of alkali (potassa and soda), 1 equivalent of alumina, with
6 equivalents of lime under the influence of chloride of si-licium.
Similar mixtures have produced crystals of garnet, idocrase, phenakite,
emerald, euclase, zircon, and wilhelm-' ite. He also produced
tourmaline in regular hexagonal prisms, which were grouped upon quartz
crystals just as they are often observed in crystalline rocks of shorl.
By the same method, but replacing the chloride of aluminum for action
upon the bases, he obtained corundum crystals, spinelle crystals, and
garnet crystals; by the contact ol perehloride of iron with chloride of
zinc he obtained fine crystals of franklinite; crystals-of magnesia or
periclase, like those from Mount Somma, were produced by the action of
lime on chloride of magnesium, but remarkable enough, their production
is just the counterpart of the origin of the native mineral, where
constantly chlorine vapors are disengaged, and where it detaches itself
from the dolomite geodes.
Mr.
Durocher obtained, by the action of sulphuretted " hydrogen gas upon
the chlorides of iron and zinc, crystals of magnetic pyrites and blende
; he also obtained, by the action of different vapors, sulphurets of
antimony and arsenic, and the gray antimonial copper.
Mr.
Senarmont obtains quartz crystals in perfect hexagonal prisms, with
all the other specific characters, from the gelatinized silica, under a
high temperature and the high pressure of thirty atmospheres.
The artificial production of the diamond has been latterly-effected by the ingenious contrivance of Despretz, which
