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FIRE IN THE EARTH
these
zircon also crystallized. All were present in magma before its eruption
and eventual solidification into the rock we now call blue ground (or
kimberlite). It is therefore reasonable to assume that only solid
inclusions possible in the diamond would be those minerals already
referred to above as having crystallized out of the magma. Besides the
minerals, the diamond itself forms a very important "inclusion." There
are many cases of a diamond's crystallizing around another diamond, the
inner diamond often differing in crystal form and color from the
outside crystal.
This
"inner diamond" is important. You will rarely hear about it because it
is partly surrounded by some dark material, and in cutting the two may
be separated. For instance, a sharp-edged greenish diamond of
octahedral form has been found enclosed in a yellow rhombic
dodecahedron, with no impurities between the two diamonds. But the most
common "inclusion" in diamonds, is a black mineral, which may be
graphite, magnetite, or solidified particles of the original magma.
Black
specks or flaws, as they are called in the diamond trade, are so
numerous that I decided to make a very careful study of these
inclusions [says Mr. Williams], with the result that I found most of
them to be particles of the original magma. It is not contended that
the plutonic magma, from which the kimberlite (or blue ground) magma is
supposed to have been derived, solidified on the first diamond crystal
and at a latter date this material, together with the first diamond,
became an inclusion in the second diamond. What appears to have taken
place is that a cluster of what has been referred to as the transported
minerals became attached to the first diamond, and that these minerals,
together with the original diamond, became an inclusion in the second
diamond.
He
adds that from examinations carried out from time to time by himself he
is convinced that, during the growth of the diamond crystal, many of
the primary minerals that had
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