THE BOOK OF DIAMONDS
diamond
mines there is a gradual decrease in the yield of diamonds as the mines
become deeper. There is no exception to this rule, and it can only be
accounted for by the carbon supply in the original magma giving out, or
by the conditions in the magma under which the carbon could crystallize
into diamond becoming such that crystallization does not take place.
The yield per load of sixteen cubic feet of blue ground from the
surface workings of Kimberley mine was 1.33 carats, while that of the
blue ground on the 3,520 foot level was .30 of a carat. What is true of
the Kimberley mine is true of all other mines.
For
years there has been a feeling among river diggers and expert diamond
sorters that there is a difference between diamonds produced from
mines and diamonds recovered from the alluvial diggers. With the
exception of the worn surface of some alluvial diamonds Alpheus F.
Williams has never been able to see this difference.
The
geological studies made on the different rocks in which crystalline
carbon is found establish indisputably that the diamond is not a vein
mineral. No crystal has been found on a rock which serves as its
support. Sometimes diamonds are found in alluvial sands, sometimes in
soft conglomerates or in a serpentine breccia.
Lewis and Randall1
assume that if diamonds were formed in nature under conditions in which
they represent the stable form of carbon they must have been produced
at least fifteen miles below the surface of the earth.
The theory that the diamonds must have crystallized in
1 Lewis and Randall, Theim. Dyn., p. 571.
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