|
cut with its own powder, and that the removal of the skin in a natural stone made a great change in the stone.
In
the fifteenth century, it became very popular and during the next two
centuries, India had a flourishing diamond trade. Alas! the discovery
of the rich Brazilian fields in 1725 dealt a death blow to the diamond
fields of India. In the latter half of the nineteenth century, the
discovery of the rich African fields proved also a disaster to the
Brazilian fields. Nevertheless, India still holds the reputation for
having produced some of the finest and largest diamonds. South Africa
now produces 95% of the world's diamonds, whereas the Indian production
is almost negligible. The world's aggregate diamond production till
about 1937 has been estimated at about 279 million carats or roughly
about 61-5 tons. Now the world's average annual production has
exceeded 10 million carats. The production was first from gravels, then
from pipe mines, which have been in turn superseded by the alluvial
deposits as the chief producers.
II. Physical properties, etc.
Diamond
crystallizes in the cubic system, the common forms being octahedron,
rhombic dodecahedron, tetra-kis-hexahedron and spinel twins. The
crystals are usually small, but larger crystals may also occasionally
be found. The Indian stones are usually octahedrons, whereas the
Brazilian stones are dodecahedrons. The Panna stones are
hexakis-octahedron, tetrakis-hexahedron and hexakis-tetrahedron. The
most common form is the octahedron, but the edges are not sharp and
tend to curvatures near the corners, giving a rounded outline to the
whole. Corners may not be present in some. In dodecahedrons the edges
and corners are much sharper than in octahedron. The cube faces may be
present as replacement forms in better diamonds. Irregular crystals are
more numerous than those of good shape.
67
|
||
|
|
||