The
diamond is generally conceded to be the most beautiful as it is the
most important of precious stones. A few other stones exceed it in
value, weight for weight; but in total importance as an article of
commerce other gems are hardly to be compared with it. Out of thirteen
and one-half millions of dollars' worth of precious stones imported
into the United States in 1900, twelve million dollars' worth were
diamonds. Not all this amount was employed for jewelry, since there is
a large utilization of the stone for industrial purposes; but even for
jewelry the diamond has a largely preponderating use. Its points of
superiority are its hardness, its high refractive powers, and its
adamantine luster. In all these qualities it excels any other known
mineral. When in addition to these it exhibits different body colors,
as is sometimes the case, the most highly prized of gems are produced.
In
composition the diamond is pure carbon, thus not differing chemically
from graphite, or such forms of carbon as lamp-black, bone-black, etc.
It is crystallized, but this can be said of graphite as well. Why
carbon should assume the form of diamond in one case and graphite in
another, as well as being amorphous in other occurrences, is not known.
Such behavior of a substance is known as dimorphism, and numerous
illustrations of it are to be found in nature.
Being
pure carbon, diamond can be burned in the air. The finely divided dust
can be burned in the ordinary blow-pipe flame, and for stones of
ordinary size a temperature of about 900° C. is sufficient. The
possibility of consuming the diamond by heat is said first to have been
suggested by Sir Isaac Newton, who reasoned from the high refractive
index of the stone that it was " an unctuous substance coagulated," and
hence probably combustible. Following this suggestion two Italians,
Averani and Targioni, succeeded, in 1695, in burning some diamonds in a
furnace, and since then the experiment has been repeated many times.
The diamond does not fuse in burning, but after becoming heated to
redness gradually grows smaller, emitting sparks, till it entirely
disappears. It leaves no ash, except in the case of the impure form
known as carbonado. The gas given off has
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