Kimherley Diamonds: Especially Cleavage Diamonds. 87 
Another guess that might be made is that the diamond crystallised 
about the garnet at some pretty high temperature, and that the relative 
expansion of garnet as compared with diamond was less than it might have 
been at some later lower temperature. In this case it would be the cooling 
as plutonic activity died away that would set up the fracturing. 
Whether we accept either alternative or neither, it is certain that dia- 
monds do cleave freely across foreign crystal inclusions. Here is a case in 
point : A very fine diamond, weighing 42 carats and valued at over .£600, 
was recently found in the Wesselton wash. It is a fair- shaped octahedron, 
as Cape octahedra go, and is much indented with the shallow triangular 
depressions characteristic of its mine. It contains the most lovely inclusions 
one can imagine — one apparently a small garnet, another a honey-coloured 
zircon, just deep enough in colour to show, very faintly, two colours in the 
dichroscope, of fair size. Through, and surrounding the position of, the 
supposed garnet is an extensive crack, while both above and below the zircon, 
and tangential to it, are similar cracks. These cracks are parallel to con- 
tiguous faces of the diamond, and neither reaches the surface of the latter.* 
The zircon with the two parallel cracks touching it exhibits an odd resem- 
blance to an airplane in flight. Under the polariscope a state of great 
internal strain is manifested over a large area in the region of the zircon by 
a most magnificent coloration, while the zircon itself is equally splendid. 
Words indeed are insufiicient to describe the chromatic beauty of the polari- 
scopic view. Curiously, there appears to be no strain to speak of in the 
vicinity of the crack through the garnet, as though the strain which once 
must have existed there and caused the crack had been relieved. 
Of course, one would expect more strain in general about a zircon inclu- 
sion than about a garnet one because of the somewhat greater coefficient of 
thermal expansion of the latter, especially along one of its crystal axes. 
This outstanding specimen illustrates very well the force of the two alterna- 
tives mooted above. For as internal strain still persists in spite of the 
present moderate temperature of the stone, it would appear that either the 
diamond must have crystallised at a surprisingly low temperature or at some 
high one at which its coefficient of thermal expansion must have been rela- 
tively greater, compared with that of the zircon, than it is now. 
Arising out of the condition of the specimen in question an interesting 
point emerges : 
Some broken diamonds, as we have said, show rounded holes in their 
cleavage faces, but others do not. Now we cannot conclude that those which 
do not show the holes were not broken by the expansion of a foreign mineral 
inclusion ; for if the cracks bounding the zircon in our specimen were to 
spread outwards all round to the diamond faces, it looks as though, from 
their position, neither of the two outer fragments, of the three into which 
* In another, similar, case the cracks did reach the surface. 
