92 
Transactions of the Royal Society of South Africa. 
end at the grease tables. Moreover, should it be a thick coating and com- 
pletely enclose a diamond, and survive intact, the diamond would certainly 
be rejected by the grease tables like the superfluous concentrates ; or, in case 
of dry sorting, probably rejected as a valueless piece of white mineral. The 
chances are therefore not altogether favourable for the detection of a diamond 
with a thick coating. Nevertheless diamonds heavily coated with a more or 
less complete shell are occasionally found. They come mostly from the 
interesting Bultfontein Mine, doubtless partly because the prevailing 
striated surface of Bultfontein diamond holds the coating best, and partly 
because of the abundance of calcite there ; but they are found occasionally 
at Wesselton and Dutoitspan. 
A significant fact about these particular lime-coated diamonds from blue 
ground is that the coating is not aragonite. For when it is boiled with 
cobalt ^nitrate it remains uncoloured. It is evident, therefore, that the 
coating was acquired at a late stage in the history of the matrix, and at a 
low temperature. 
Equally significant is the fact that calcite is not found inside cracked 
diamonds from the Kimberley area. The filling material has been taken 
from the cracks of many diamonds on the De Beers sorting tables and in 
no case has it been calcite. Usually it appears to be apophyllite,* and 
pectolite has been found. Hence it may reasonably be inferred that the 
cracking of the diamonds took place at a relatively early period, and that 
the cracks became filled with a zeolite, or something of that sort, before the 
calcite was introduced, or separated out, into the matrix. t Which is yet 
another argument against the popular delusion that cleavages among 
diamonds are due to explosion after the diamonds are taken from their matrix. 
Occasional Dutoitspan rounded yellow diamonds are reported which 
have failed to adhere to the grease tables. They carry no obvious foreign 
coating any more than the Wesselton yellow-ground diamonds did, but 
presumably they carry a coating even though it be indefinitely thin. And it 
may be surmised that they come from the vicinity of local accumulations of 
calcite in the pipe rock. One typical specimen that had been rejected by all 
three tables adhered to the grease quite normally after immersion in a 
weak acid. 
It may be of interest to quote here some remarks made by Boutan in 
his great work ' Le Diamant,' 1886, p. 171. Speaking from actual expe- 
rience of Kimberley as it was somewhere about 1884 — i. e. at a time when 
the blue ground had been reached and was being worked, he says of the 
diamond : 
" II se presente sous bien des etats divers de cristallisation, de couleur 
* Cf. ' The Diamond Mines of South Africa/ p. 507. 
t Cf. F. P. Mennell, 'The Miner's Guide,' 1909, p. 147; also P. A. Wagner, 
' The Diamond Fields of Southern Africa,' 1914, p. 75. 
