one
inquiring whether diamonds grow again after three or four years in the
same places where they have been dug out. The answer sent back was,
"Never, or at least as the memory of man can remember."
The
most generally accepted theory is that diamonds are a form of carbon
produced by heat and pressure, but how Nature obtained the carbon, held
it inert from its affinities, and subjected it to the necessary forces,
still keeps scientists guessing. The fact that some diamonds taken
from the African mines burst as artificial ones do is accepted as
evidence that they were formed under great pressure. Diamonds in
different mines have different forms of crystals, and properties,
therefore, must have been formed under different conditions.
Liebig,
Dana and others concluded that diamond is the product of the gradual
decay of organic matter under influences at present unknown. The
theory advanced by Professor Carvill Lewis, that the carbon was
derived from carbonaceous shales decomposed by the action of an
igneous magma forced through them by volcanic action, is considered
disproved by the fact that there are no carbonaceous shales in the
pipes near Pretoria though they contain many diamonds. Such shales do
overlay the lower strata surrounding most diamond pipes and, as the
volcanic filling of the Pretoria pipes may have come from foreign
sources, the theory is tenable.
Some
have thought that diamonds may have been formed from anthracite coal,
possibly without passing from a solid state. Several eminent men
advocated the theory that pure
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