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Transactions of the Boyal Society of South Africa. 
ture to wliicli tliey are exposed in the ordinary way of mining* ; or (3) are 
in the condition of Eupert's drops.f 
In other words, diamonds have not been known to burst, and, besides? 
there is no certain reason why they should do so. This was a principal 
argument in " Kimberley Diamonds : Especially Cleavage Diamonds " 
(' Trans. E.S.S.A.,' 1918), and it is proposed to amplify it here, to answer 
some of the criticisms which have been launched against it, as well as to try 
to explain how the idea of bursting arose. Here the verb " to burst " is 
used in the ordinary sense as defined by the ' Oxford Dictionary ' : "To 
break suddenly, snap, crack, under violent pressure, strain or concussion. 
Chiefly said of things possessing considerable capacity for resistance, and 
breaking with a loud noise." That the verb has been understood in this 
sense, and not merely in that of a gentle breaking, disintegrating, pulveris- 
ing, is evident since "to explode" is used as its equivalent,^ and the 
behaviour of Rupert's drops has been invoked by way of illustration. 
A friend writes me the following interesting remarks : 
" I can form but little notion as to the extent to which your paper 
on Kimberley Diamonds may have reached the eyes of early diggers, 
of whom I was one as you know; but I am very sure that each one of 
such has been surprised at what you have written under the heading 
of ' Spontaneous Breaking.' To each this phenomenon is an esta- 
blished fact, and as such offering no possible ground for argument. 
The stones most liable to break up were sharp-edged octahedrons such 
as are most plentiful amongst the finds in the western portion of 
Kimberley Mine and (so far as I can recall) in Kimberley Mine only. 
In very many cases these stones had a more or less perceptible smoky 
cloud in one corner, and it became quickly known that such stones 
generally broke up spontaneously sooner or later. Various treatment 
was resorted to in the hope of saving, e. q. embedding in potato, 
wrapping in oil-rag or cotton-wool, and no doubt others of which I 
* Cf. Sorby and Butler, " On the Structure of Rubies, Sapphires, Diamonds, 
etc. " : — Brewster " thought that the black specks, which were surrounded by a black 
cross when examined with polarised light, were minute cavities; but at the same 
time he admitted that they were so small that it was not possible to say whether 
they contained a fluid or were empty. Judging from what we have seen of such small 
examples, we consider it impossible to say whether they are cavities or enclosed 
crystals/' ' Proc. E.S.,^ 1869. 
t Some artificial diamonds may be likened to Kupert's drops — perhaps because 
they have been cooled too quickly. Crookes, in his magnificent Kimberley lecture, 
mentioned one which biu-st and covered with fragments the slide upon which it was 
mounted. 
X E.g. — " It is notorious that the strain is occasionally so great that a diamond 
explodes into powder shortly after removal from its enveloping matrix of blue clay." 
A. E. H. Tutton, 'Crystals,' 1911, p. 207. 
