thought
he had found microscopic diamonds in xanthophyl-lite from the Urals,
the diamonds, in the form of hexa-kistetrahedrons, being held to be
very abundant; but Professor Knop,1 after a very painstaking
and convincing examination, proved the supposed diamonds to be merely
holes in the xanthophyllite, the holes being probably negative crystals
due to corrosion. By rubbing copper oxide on a dry slide he filled
these holes with the black powder.
Another supposed discovery of diamonds in the matrix was announced by Fouque and Levy,2
in 1879. They thought that they had observed numerous small diamonds in
a thin section of the diabase, the so-called ' ophite andesitique,'
which forms overflow sheets in the Karoo shales, and they published
photographs of these supposed diamonds in sections. But, as they
afterwards found,3 these also were only holes.
The
very minute, isotropic, highly refracting crystals occasionally seen in
a thin section of the Kirnberley peridotite are certainly not holes,
for they are sometimes of a faint yellowish, or, more frequently,
bluish colour, and are often entirely embedded in the ground-mass. They
never occur as enclosures in other minerals, but, like the perovskite,
lie scattered in the ground-mass only; belonging, therefore, to a later
generation of minerals than the olivine and bronzite. They are always
in the form of entire crystals, even in
the thinnest slide, as if they were too hard to be cut. The shape is that of an octahedron with rounded faces ; tri-
