84 
Transactions of the Boyal Society of South Africa. 
probably not touching 40° C. A large flow of water met with in the main 
rock tunnel at a depth of 1625 ft. in the Kimberley Mine had a temperature 
of about 30° C. (84° F.). 
The theory that diamonds were broken by violent movements of the 
kimberlite does not explain the cause of the breakages among diamonds 
found in gravels, unless we may conclude that these diamonds were brought 
to the surface in outbursts of plutonic energy. Perhaps they were not so 
brought. 
Again, a yellow diamond recently examined, having a very striated 
surface which prevented its interior from being properly seen, showed a 
crack running half the way round the outside of the stone. The polariscope 
indicated a great state of strain somewhere near the centre of the stone at a 
place Avhere the crack seemed to extend inwards to. Now, if the expansion 
of contained gas had caused the stone to split, the gas must have escaped 
through the crack. Why, then, the continued strain? Again, where could 
the internal strain have come from if the stone had been broken by concus- 
sion in machinery or pipe ? The De Beers Company has a diamond with a 
percussion figure like a clock-face under its surface, and in this case the 
shock which made the figure has set up no internal strain. We shall see in 
the following section how the strain and crack in the above yellow diamond 
have probably arisen. 
12. Suggested Eeasons for Breaking ; Mineral Inclusions, etc. 
The suggestion now to be put forward, with all deference to better 
authorities, is that the circumstance of broken diamonds on a large scale 
is not alone due to : 
(1) Either the spontaneous breaking up of those that are smoky or 
brown, or any other colour ; 
(2) Or to breaking in the process of mining and winning ; 
(3) Or to violent movements of the kimberlite in past time ; 
(4) Or to the expansion of contained gases within the diamonds whether 
by heating or relief of pressure outside, 
though each or any of these actions may have been of some effect ; but 
principally to the energy exerted by the mineral inclusions so often con- 
tained in diamonds. These inclusions are most frequently garnet, and there 
are, besides, zircon, ilmenite, iron pyrites, and (possibly) chrysolite.* There 
are also inclusions of what may loosely be called splotches of graphite (very 
numerous), oxide of iron, and chrome diopside (rare). Some of the black 
inclusions may be either ilmenite or haematite, or graphite, but they are 
* Or enstatite : " A bright green variety occurs in large cleavable fragments in 
the diamond-bearing detritus of Colesberg Koppje in the Transvaal " ! — H. Bauerman^ 
Text book of Descriptive Mineralogy/ 1897. Some of this material is harder than 
windo^v glass. 
