INDUSTRIAL DIAMONDS: IN WAR AND PEACE
arranged,
however, that it is practically impossible to saw this form of boart
with the ordinary diamond saw. A piece of framesite boart (which, if it
had been an ordinary diamond, would have taken six or seven hours to
cut) was placed under the diamond saw for a continuous running time of
three days without the slightest cut being noticeable.
Finally,
there is shot boart, the aristocrat of the boarts, deriving its name
from its peculiar spherical form. It is supposed to be at the top of
the scale of hardness for the different varieties of diamond. For this
reason it is much used in diamond-boring machinery. It is opaque and
ranges in color from a milky-white to a steely gray. It is never found
showing any crystalline faces or edges, nor does it show any definite
line of cleavage. It does not have inclusions of diamond of
crystalline form, as in the case of common boart, nor inclusions of
garnet, ilmenite, or chrome-diopside, as have some diamonds.
The
next type of industrial is carbon. It is more popularly known in the
trade, I believe, as carbonado, singular; carbonadoes, plural. When
first discovered in Brazil, carbonadoes were considered of little
value because experts could not accept them as gem diamonds. Today they
are used industrially with frequency, even though they are not as good
a quality as the South African industrials. They are found of
considerable size, one of the stones weighing 3078 carats, in the
province of Bahia. As used industrially, they consist either of
complete unbroken stones or of pieces of large carbonadoes.
Ballas
is another type of industrial. It possesses many of the characteristics
of carbonadoes and also is found in Brazil, although it is obtainable
from the Jagersfontein mine
(247)
