largest specimen found (1895) weighed 3078 carats. Both bort and
carbonado seem to be really aggregates of crystallized diamond, but the
carbonado is so nearly structureless that it was till recently regarded
as an amorphous modification of carbon.

_Uses of the Diamond._--The use of the diamond for other purposes than
jewelry depends upon its extreme hardness: it has always been the only
material used for cutting or engraving the diamond itself. The
employment of powdered bort and the lapidary's wheel for faceting
diamonds was introduced by L. von Berquen of Bruges in 1476. Diamonds
are now employed not only for faceting precious stones, but also for
cutting and drilling glass, porcelain, &c,; for fine engraving such as
scales; in dentistry for drilling; as a turning tool for electric-light
carbons, hard rubber, &c.; and occasionally for finishing accurate
turning work such as the axle of a transit instrument. For these tools
the stone is actually shaped to the best form: it is now electroplated
before being set in its metal mount in order to secure a firm fastening.
It is also used for bearings in watches and electric meters. The best
glaziers' diamonds are chosen from crystals such that a natural curved
edge can be used. For rock drills, and revolving saws for stone cutting,
either diamond, bort or carbonado is employed, set in steel tubes, disks
or bands. Rock drilling is the most important industrial application;
and for this, owing to its freedom from cleavage, the carbonado is more
highly prized than diamond; it is broken into fragments about 3 carats
in weight; and in 1905 the value of carbonado was no less than from L10
to L14 a carat. It has been found that the "carbons" in drills can
safely be subjected to a pressure of over 60 kilograms per square
millimetre, and a speed of 25 metres per second. A recent application of
the diamond is for wire drawing; a hole tapering towards the centre is
drilled through a diamond, and the metal is drawn through this. No other
tool is so endurable, or gives such uniform thickness of wire.

_Distribution and Mining._--The most important localities for diamonds
have been: (1) India, where they were mined from the earliest times till
the close of the 19th century; (2) South America, where they have been
mined since the middle of the 18th century; and (3) South Africa, to
which almost the whole of the diamond-mining industry has been
transferred since 1870.

_India._--The d