It is black, opaque, vitreous, of an irregular form, and of a specific weight of 3-782.
Its
most precious quality, and that which alone would distinguish it from
every other mineral at all resembling it, is its prodigious hardness,
which quite equals that of the diamond.
This
mineral, which is found in pieces varying from the weight of one to a
thousand carats, has, since its discovery, been constantly used, in the
same way as diamond dust, to cut and polish the diamond. It is also
used in making certain graving tools capable of cutting gems of any
degree of hardness.
Sometimes
pieces of this carbon are found which have an evident principle of
crystallization, and present a number of small, bright, white points,
which, however, are devoid of transparency.
It
appears that this is the raw material of the diamond before
crystallization ; in other words, carbon, in the last stage of density.
Nevertheless, we must acknowledge that this substance is different
from the diamond, inasmuch as it cannot be divided in plates, which
fact is explained by its non-crystalline composition.
Subjected
to a heat of 2765°, it burns with a smoky, phosphorescent flame, much
less clear than that of the diamond during combustion. After being a
long time subjected to a great degree of heat, it is found, on
withdrawal from it, to be of the same dimensions, of equal hardness,
and still without transparency, although having lost all its black
colour, and become greyish white.
