148 THE DIAMOND MINES OF SOUTH AFRICA
mond,
in the centre of which is a little gold leaf. He had the information
from Dr. Mills Franco, who maintained that there was no deception in
its being gold.1 Occurrences of this nature tend to veil the genesis of the diamond in still further mystery.
Professor
T. G. Bonney lately obtained specimens from the Newlands mines, some
forty miles northwest of Kimberley, of a coarsely crystalline rock
studded with garnets, technically " noncrystalline allied to
eclogites," which were embedded, as he says, in typical blue ground. In
this eclogitic rock he found a number of small but perfectly formed
diamonds. At a meeting of the Royal Society in July, 1899, he presented
his conclusions: "The blue ground is not the birthplace, either of the
diamond or of the garnets, pyroxenes, olivine, and other minerals, more
or less fragmental, which it incorporates. The diamond is a constituent
of the eclogite, just as much as a zircon may be a constituent of a
granite or a syenite.
"
Though the occurrence of diamonds in rocks with a high percentage of
silica (itacolumite, granite, etc.) has been asserted, the statement
needs corroboration. This form of crystallized carbon hitherto has been
found only in meteoric iron (Canon Diablo), and has been produced
artificially by Moissan and others with the same metal as matrix. But
in eclogite the silica percentage is at least as high as in dolerite;
hence it is difficult to understand how so small an amount of carbon
escaped oxidation.
"
I had always expected that a peridotite (as supposed by Professor
Lewis), if not a material yet more basic, would prove to be the
birthplace of the diamond. Can it possibly be a derivative mineral,
even in the eclogite ? Had it already crystallized out of a more basic
magma, which, however, was still molten when one more acid was injected
and the mixture became such as to form eclogite ? But I content myself
with indicating a difficulty and suggesting a possibility; the fact
itself is indisputable : that the diamond occurs, though rather
sporadically, as a constituent of an eclogite, which rock, according to
the ordinary rules of inference, would be regarded as its birthplace.
