Gems and Precious Stones [pp. 393-401]

GEMS AND PRECIOUS STONES.
origin, and suggest what it might have
been. The theorist who claims a celes tial origin for them deserves praise for
his boldness at all events, and his deserts
for the validity of his suggestion are per hlaps as great as those of the many who
have sought to explain their formation
by suppositional terrestrial actions. The
sky-birth of the diamond is suggested by
a Continental experimentalist, who, upon
the strength of some preliminary researches, declares that intense cold dissociates chemical elements in combinationI. The "pure carbon" of the diamond he holds to have once been mingled with other matters, in masses of
meteoric nature, coursing through space;
and he argues that the intense cold
which reigns in stellar space (something
like two hundred degrees below zero)
has been the means of isolating and
crystallizing the carbon, and that diamonds have fallen firom the sky like the
aerolites, whose celestial source is well
known. Those Cape specimens which
attract so much attention are found on
the surface of the ground only,-it is of
no use to dig for them. This looks as
though they came down rather than up.
Be that as it may, this stone is singular
in many respects. It is the only cornmbustible and the only elementary substance which is used as a gem. It is the
hardest material known, and its refractive and dispersive powers on light are
higher tlhan those of any other precious
stone. It is also one of the miost unalterable. It is not affected by chemicals,
is infusible, only to be consumed by exposure to a long-continued or very high
temperature, and these qualities, combined with its rare brilliancy, make it the
most valuable of precious stones. It is
also likely to become as useful as it is
ornamental. The diamond drill is the
only drill that can bore its way through
certain rocks whose hardness soon dulls
the best steel drills. And now a diamond
saw has been invented, which promises
to do with stone what the finest steel saw
does with wvood. It consists of a thin
metal disk, the teeth of which are nothing
more than minute black diamonds, embedded in the metallic edge of the sheet.
When revolving at a high speed, this
disk cuts into the sides of a stone slab
as though it were a piece of timber; and
not only can straight cuttings be made,
but, by an ingenious mechanical device,
bevels and rounded edges are cut. As
a labor-saving machine, the inventor
judges that one of them will do the work
of fourteen stone-cutters.
The diamondlis pure carbon, chemically almost the same as graphite, or
plumbago, and charcoal, but very different from them in its transparency and
luster. It is generally found in octahedral crystals, having highly polished faces,
and although possessing some beauty in
this natural state,-owinig to the high luster of the faces,-yet it has not a tithe
of the splendor exhibited by a well-cutt
brilliant. The ancients did not know
how to cut the extremely hard diamond,
and were content to wear it in its natural
state, but even thus they prized it highly.
In I456, Louis Berquen, a Belgian,
brought the art of diamond-cutting to a
high state of perfection, and it is now
carried on chiefly in Amsterdam by the
Jews. Nothing but diamond will cut diamond, and therefore the stones are first
roughly shaped. by cleaving off slices of
the gems and rubbing twvo stones together. Afterward they are brought to
the exact shape required, and finely polished by grinding against a very swiftly
revolving disk of soft steel, smeared with
oil and diamond-dust. On this operation of cutting depends thte brilliancy and
consequent value of the gem; and as
diamonds are sold by weight, there is a
great tendency so to cut the stone that it
may weigh as much as possible. This,
however, is regarded by eminent technologists as a great error. Says Professor Cornwvall: "As a stone miust be cut
in a certain way in order to develop the
most perfect luster, any additional weight
inevitably injures the effect of the cutting."
The most common form of cut diamonds is the well-known brilliant, famil
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