GEMS AND PRECIOUS STONES. 11
Green diamonds of good colour are also rare and valuable, a specimen at
Dresden weighing 48-1/2 carats being valued at £30,000.
In the celebrated Townshend collection are included diamonds having
black, yellow, green, grey, indigo, cinnamon, and other colours. This collec-
tion was presented by the Rev. Chauncy Hare Townshend, in 1869, to the
South Kensington Museum, and contains 154 specimens.
"Bort,"
or "Boort," is a name given to an uncrystallized form of diamond. It is
crushed to form " diamond dust" for polishing purposes. It may be as
well to mention here that those diamonds that are too bad for cutting
as gems are known as " bort," and are crushed for polishing and cutting
purposes. It has been stated that a specimen of "bort" was obtained
near Bathurst. It would certainly be advisable to keep this substance
in mind when seeking for gems.
"Carbonado"
is an opaque, very hard form of carbon—as hard as the diamond. It is
only found in Brazil at present. It is used for polishing, and for the
manufacture of "diamond drills" for deep borings. The demand for it for
these purposes has increased its value, it being worth at one time 30s.
per carat.
Geological Formation.
In
New South "Wales, diamonds are principally obtained from the tertiary
gravels and recent drifts; but it is hardly to be supposed that they
were formed in these tertiary deposits. They, no doubt, originally had
a home in some older formation, and it certainly is desirable that this
secret dwelling-place should be discovered. This may probably be
metamorphosed rocks.
Under
what conditions diamonds have been formed is at present unknown, so
that we cannot presume to suggest the kind of formation most likely to
contain them. The operation of excessive heat in their formation seems
hardly probable, on account of the combustible nature of the diamond.
Whether the carbon was derived from animal, vegetable, or other
sources, is also unknown, but the presence of the diamond in mica-slate
does not favour the idea of vegetable origin.
There
is not the smallest doubt that the enormous yield of diamonds from the
" Kimberley diggings" of South Africa, is dne to the fact that there
the diamond is taken from its actual matrix, where it is found in an
intrusive rock. In this rock the diamonds are found crystallized, often
in octahedrons and allied forms. The formation in which these diamonds
are found is a very peculiar one, consisting, as it does, of material
filling a natural " pipe," with hard rock around it. The generally
accepted theory is that the " pipe" is the funnel of an extinct
volcano, and that the diamond-bearing rock which now fills it, and
forms the mine, has been upheaved from a yast depth, the diamonds being
probably of earlier date than the upheaval.
By
referring to the accompanying diagram, a good idea will be obtained of
this peculiar occurrence. It is from an official publication issued by
the Government of Cape Colony (Beport of the Inspector of Diamond
Mines, Kimberley, for 1892). Although indicating the Kimberley Mine,
the general idea will serve for the other principal mines also.
The
inevitable rush to this district set in during 1870, and it is computed
that in a short time no less than 10,000 persons were searching for
diamonds there. Since that time the diamond-fields of South Africa have
become noted for their marvellous richness, diamonds by the ton weight
having been found there. For a little over three years—18S3, 1884,
1885. and part of 1882—diamonds to the value of over £8,250,000
sterling were obtained. The value of the rough stones ranged during
that time between 20s. and 29s. per carat.
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