high temperature, and the whole substance then
disappears in carbonic acid gas. Unlike coal,
however, diamonds are usually transparent,
possessing a peculiar lustre, hence called adamantine,
and reflecting light from their inner surface.
The light entering a diamond is bent
more than in passing into any other substance
in nature. Diamond is electric, even when
rough, and possesses phosphoric and luminous
properties after being exposed to the sun for
some time. It is generally of crystalline form,
but coated over in the mine by a thick crust,
exceedingly hard. Still, even the children in
countries where they abound, can generally
detect the valuable gems in their concealment.

Diamonds require very careful cutting, so as
to diminish their weight as little as possible
consistently with ensuring the greatest amount
of internal reflecting surface belonging to their
form. Their value as gems depends greatly on
the cutting, and this, of course, to some extent,
on the original shape. What are technically
called "brilliants" are those stones that can be
cut without serious loss into the form of two
pyramids placed base to base. Of these pyramids
a slice of the one intended to be presented
to the eye is cut off, while the other, serving to
reflect light from its internal surface, although
also flattened slightly, is much the more nearly
pointed of the two. In fine brilliants the upper
pyramid has thirty-two facets, or sides, and the
lower twenty-four. Nearly half the diamond is
often wasted in cutting a brilliant, but without
it a fine stone can hardly be considered as
presenting the real beauty that belongs to it.
When, however, the form of the stone is such
as not readily to admit of this treatment, only
one pyramid is cut, and the base is embedded in
the setting, making what is called a rose diamond.
When there is a double pyramid the
setting simply clasps the girdle, or junction of
the bases of the two pyramids, and the two sets
of faces are both exposed to the action of light.
Besides these two kinds, some diamonds are cut
flat, with irregular facets; these are called table
diamonds, and their value, weight for weight, is
very inferior to that of roses and brilliants.

Diamond-cuttiug is a business in the hands
of Jews, and is chiefly carried on in Amsterdam,
where, it is said, ten thousand persons are more
or less dependent on it as an occupation. Owing
to the extreme hardness of the stone the only
means of acting on it are by rubbing two faces
of different diamonds together, or cutting the
stone by a circular steel saw covered with diamond
dust.

Diamonds are not always colourless, though
those most highly valued generally are so. The
few that are known of fair size and clear distinct
tints are even more costly than those
of purest white. There is a difference, however,
in the estimate of colour, the celebrated
blue diamond of Mr. Hope, weighing one hundred
and seventy-seven grains, and the green
diamond of the crown of Saxony, the finest
known coloured specimens, being more valuable
than if they were white. The yellow varieties,
on the other hand, generally sell at lower prices
than stones of equal weight without colour.

The largest diamond known is one, uncut,
belonging to the Rajah of Mattan, in Borneo. It
weighs more than two ounces and a quarter
troy, but would probably be very greatly reduced
if properly cut. It is egg-shaped, and
indented at the smaller end. The largest regularly
cut diamond is a rose, and of yellowish
tint; it weighs one hundred and thirty-nine
and a half carats,* or nearly an ounce. The
finest brilliant is the Pitt, or Regent, diamond,
now in the French crown. It originally weighed
four hundred and ten carats, but has been reduced
to one hundred and thirty-seven by
cutting, and was sold to the Regent of France
for about one hundred thousand pounds. Our
Koh-i-noor, now only one hundred and two
carats, is believed to have been part of the
largest real diamond recorded; the unbroken
stone having weighed nine hundred carats. It
is supposed that the great Russian diamond,
called the Orloff, now weighing one hundred and
ninety-three carats, was originally another part
of the same stone.
* The carat is the weight used all over the world
to estimate the diamond. It originated in India,
and is equal to about three and one-sixth grains troy,
six carats being nineteen grains troy.

Diamonds are not always transparent, nor are
they only valuable for ornamentation. A vast
number are used for watches, and others for
cutting glass. There is a ready demand for
them to almost any extent, and, in spite of the
large supply, the price is by no means falling.

Next to the diamond in value, in beauty, and
in hardness, and in some cases rivalling, or even
excelling it in the two former properties, are
the gems obtained from crystallised clay. Strange
that coal and clay, the two least likely substances
to possess any intimate relations with
beauty and hardness, should, in their crystalline
forms, excel all others in both these respects!
Not more strange, however, than true.

Under the name of RUBY and SAPPHIRE the
red and blue varieties of crystallised clay are
well known to the world. They are almost all
obtained from Pegu, Ava, and the island of
Ceylon: a singularly limited region for what
one might expect would be much more widely
distributed. Like the diamond, they are obtained
by washing gravel, and all the varieties
occur in the same district. These varieties
include the Oriental sapphire, the Oriental ruby,
the opalescent ruby, the star ruby, the green,
yellow, and white sapphires, and the Oriental
amethyst. Most of these are extremely rare,
and all the finest specimens are believed to be
still retained in the East. As, however, these
stones of Eastern princes are rarely cut, and no
doubt many of them would be found affected
with flaws, their real money value if in the
market would be very inferior to their
estimated value.

There is a useful mineral of extreme hardness
—the corundum of commerce, from which the
hardest and finest emery is obtained— which is an