Herbert, and put the book by; but we neither of us
said anything, and both looked at Provis as he
stood smoking by the fire.

THE TREASURES OF THE EARTH.

IN TWO CHAPTERS. CHAPTER II.

IT is a curious fact, that while most of the
stones called " precious " were worn in former
times as amulets, to ward off danger and
mischief, and were valued greatly for such
purposes, and while almost all the varieties of
agate had special uses, the onyx was
considered to excite spleen, melancholy, and mental
disturbance in the wearer, especially when used
as a neck ornament. As, however, the ordinary
agate was worn to calm pain and sooth
the mind, and the mere scent of some varieties
—a peculiarity and difficult thing to ascertain
the existence of— would turn away tempests,
even arresting the impetuosity of torrents, the
line of distinction must have been very nicely
drawn. So active were stones of this kind
supposed to be, that the celebrated Milo of Crotona
is said to have been indebted to a certain chalcedonyx
that he wore, for the execution of his
feats of wonderful strength. Of the other
stones, the beautiful heliotrope, or blood-stone,
was thought to render the wearer invisible,
while jasper would stop any excess of bleeding
arising from natural causes.

All the minerals here mentioned consist of
quartz or silica, combined, when coloured, with
a small quantity of metallic oxides and earthy
minerals. Thus the amethyst and other violet
and blue colours are produced by manganese,
and the rose tint is owing to the same metal.
Almost all the reds are due to iron, and the
yellow and green to very minute quantities of
minerals not very clearly determined. The
brown of cairngorm is the result of a little
bitumen.

It is astonishing to consider how very small
a quantity of foreign material will sometimes
alter the character and appearance of crystals.
Thus the cat's-eye is a gem of greenish tint,
milky and opal-like. When cut in a certain
way, it presents a floating white band of light,
and certain specimens emit one or more brilliant
rays, coloured or colourless, issuing apparently
from one point, and extending to the extremity
of the stone. Compared with one of those balls
of crystals sometimes cut into the same form, or
with the lens of a pair of pebble spectacles, it is
hardly possible to imagine that there is so little
difference as really exists between the two
minerals in their chemical composition. In
point of fact, the presence within the crystal of
a few delicate threads of white asbestos, seems
to produce all the modifications, except that of
colour, and the cause of the colour itself is owing
to some substance, the quantity of which is too
small to enable chemists to determine its nature.
Certainly the method of small doses, as
advocated by homoeopathists, is not without a certain
analogy in nature, and doses too small to be
appreciated by mortal chemistry are sufficient
sometimes to produce results on minerals rather
startling in their magnitude.

There is one fact with regard to specimens of
quartz—or crystals, as they are often called—
which is very curious and interesting. Small
cavities not unfrequently occur within them,
sometimes empty, but often filled with fluid.
By exposure to cold this fluid may be frozen,
and very often a slight increase of temperature
converts it into transparent vapour, while
by optical methods of examination employed
under the microscope, the properties of the
fluid can occasionally be detected. Indeed,
the cavities have been so large that the fluid
could be extracted in sufficient quantity for
examination. It might be expected that some new
element or compound would be thus obtained—
some secret of nature's laboratory —some
substance from the interior of the earth, only thus
brought within our knowledge, locked up in one
of the hard crystalline minerals elaborated far
beneath, out of our sight. No such result is
obtained, and no such mystery laid bare, for we
find almost all the cavities in question to be
occupied by water mixed only with some common
salt or acid, held in solution. Vapour of water,
then, must be contained in rocks during the
whole period of their formation in the earth,
much in the same state of admixture in which
we know that it is present in the atmosphere
to form clouds. Thus these wonders of nature
and treasures of art are the result of some
process only the more wonderful because it is so
extremely simple, being one by whose agency
ordinary familiar substances are worked up,
together with water, under certain conditions of
heat, bringing about in this way the magic of
our most varied and beautiful gems.

Mixed with water in a different way—the
water distributed in every part, and not collected
in cavities—the same mineral, quartz or silica,
becomes that very curious and fantastic stone,
the opal. The proper colour of this gem is a
peculiar pearl grey, showing a fluctuating pale
red, or wine yellow tint, when seen between
the eye and the light. With reflected light it
presents all the colours of the rainbow, showing
a flame-red, violet, purple, blue, emerald
green, and golden yellow. The rays of light
and colour shoot forth from a, fine opal (noble
opal, in technical language) with the most vivid
effulgence, and the more flaws it contains the
more does it reflect, and the greater value is
attached to it. In some rare cases, opals have
been found nearly black, but glowing like a fine
ruby. Other opals are spangled, and sometimes
not more than one colour is seen. In all cases,
however, the foundation of the stone independent
of the colour, which is entirely an optical
effect, consists of a peculiar milky translucent
mass, which at once marks the gem.

Opals are very rarely found of large size, the
dimensions of a hazel-nut or walnut being
seldom exceeded. They are never cut in facets,
and are generally set surrounded by brilliants,
whose bright dazzling reflections contrast well
with the calm moon-like beauty and rich soft