Brazil;
the rhombic dodecahedron is also seen in Brazilian specimens; crystals
from the Urals usually show the four-faced cube according to Parrot;
Indian and South African crystals are more frequently octahedral in
habit, though not necessarily having the octahedral face itself largely
developed.
The
variety of Diamond known as Bort (also spelled Boort and Boart) occurs
in rounded forms, having a confused crystalline structure, and hence
no definite external crystallised form, and no definite cleavage. In
colour it is usually grey or black, the lustre is greasy, the specific
gravity less than of the crystallised variety and the hardness
slightly greater. There seems to be a regular gradation from one of
these varieties to the other, and also from Bort to Carbonado. Although
useless as a gem, Bort is very valuable for many technical purposes
which will be mentioned later. In the Diamond trade not only is the
term used as here, but any specimen of the crystallised variety which
by reason of bad colour, flaws, deficient size, or other cause, is
unfit to cut, is included under the term Bort. Carbonado is the same
mineral in a still more confused state of aggregation; frequently it is
called Black Diamond, but as under that term it might be confused with
the black varieties of the true Diamond, it is better to adhere to the
mineralogical term. Carbonado may be granular, or quite compact; it
shows no cleavage. Its hardness may be greater than Diamond in
crystals, but it is less brittle, and thus is also largely used in
technical processes. Its specific gravity is less than Diamond proper,
possibly due to some degree of porosity. It chiefly comes from the
Serra da Cincora, in the state of Bahia in Brazil, where it is found in
