amiliar to the Romans until introduced from India, where it
was probably mined at a very early period. But one or other of the
remaining varieties mentioned by Pliny (the Macedonian, the Arabian, the
Cyprian, &c.) may be the true diamond, which was in great request for
the tool of the gem-engraver. Later Roman authors mentioned various
rivers in India as yielding the _Adamas_ among their sands. The name
_Adamas_ became corrupted into the forms _adamant_, _diamaunt_,
_diamant_, _diamond_; but the same word, owing to a medieval
misinterpretation which derived it from _adamare_ (compare the French
word _aimant_), was also applied to the lodestone.

Like all the precious stones, the diamond was credited with many
marvellous virtues; among others the power of averting insanity, and of
rendering poison harmless; and in the middle ages it was known as the
"pietra della reconciliazione," as the peacemaker between husband and
wife.

_Scientific Characters._--The majority of minerals are found most
commonly in masses which can with difficulty be recognized as aggregates
of crystalline grains, and occur comparatively seldom as distinct
crystals; but the diamond is almost always found in single crystals,
which show no signs of previous attachment to any matrix; the stones
were, until the discovery of the South African mines, almost entirely
derived from sands or gravels, but owing to the hardness of the mineral
it is rarely, if ever, water-worn, and the crystals are often very
perfect. The crystals belong to the cubic system, generally assuming the
form of the octahedron (fig. 1), but they may, in accordance with the
principles of crystallography, also occur in other forms symmetrically
derived from the octahedron,--for example, the cube, the 12-faced figure
known as the rhombic dodecahedron (fig. 2), or the 48-faced figure known
as the hexakis-octahedron (fig. 3), or in combinations of these. The
octahedron faces are usually smooth; most of the other faces are rounded
(fig. 4). The cube faces are rough with protruding points. The cube is
sometimes found in Brazil, but is very rare among the S. African stones;
and the dodecahedron is perhaps more common in Brazil than elsewhere.
There is often a furrow running along the edges of the octahedron, or
across the edges of the cube, and this indicates that the apparently
simple crystal may really consist of eight individuals meeting at the
centre; or, what comes to the same thing, of tw