Kimherley Diamonds : Especially Cleavage Diamonds. 85 
so small that specific gravity tests (the only tests that are available without 
breaking the diamond) are not delicate enough to determine which. 
Diamonds possibly tinted by dio2)side have turned up now and then ; but 
only one hitherto in our mines, containing a definite splotch of the material. 
But some years ago a beautiful specimen of a diamond was found in the 
Voerspoed Mine (O.F.S.), which contained a number of bright green 
splotches, doubtless diopside. This stone is now in the possession of Gr. F. 
Williams, and is probably peerless of its kind for beauty. A genuine 
crystal of chrome diopside has yet to be found in a Cape diamond ; although 
it has been met with in bort. 
Bauer (p. 192) states that " until recently no diamond had ever been 
observed attached to another mineral in such a way as to suggest that 
the two grew side by side at the same time. The discovery, however, 
of a diamond crystal attached in this way to a garnet shows that such a 
growth does take place, though rarely." This assertion besides being bad 
science is bad history. The phenomenon is neither rare nor new. Evelyn 
relates in his diary how on Michaelmas Day, September '29, 1645, he 
visited the collection of the noble Venetian Signor Rugini where he saw 
" above all a diamond which had a very fair ruby (? garnet) growing in 
it." 
In the majority of cases the garnet, or other inclusion, is not actually 
inside the diamond, but is set more or less deeply in a cleavage face. Also 
a very great number of cleavage fragments contain somewhere in their 
fractured surfaces small rounded holes or indentations such as could scarcely 
arise in breaking unless the holes or indentations had been there first, with 
something inside them. Tliis latter circumstance indicates that diamonds 
containing inclusions have been more frequent in nature than we should 
infer from even the considerable number found with the inclusion present 
Some of these holes may possibly have contained gas or liquid. 
In trying to interpret the facts we have to bear in mind that the thermal 
expansion of pretty well all crystals, saving those of the beryl family, at 
ordinary temperatures, is much greater than that of the diamond. Between 
0° and 100° C, for example, the coefiicients of cubical thermal expansion 
are for : 
Zircon 0-2835 
Garnet 0-2543 
Quartz 0-3530 
Diamond . 0-0354 
Whether these relative values would hold under plutonic conditions of 
heat and pressure is perhaps uncertain, though the coefficient of thermal 
expansion for diamond is said by Miers to increase rapidly at high tempera- 
tures and to diminish rapidly at low ones. For our present purposes very 
high temperatures need not concern us ; nothing higher in fact than the coin- 
