92 
Transactions of the Royal Society of South Africa. 
whether the red crystal of the Burma ruby mines was to be the regular 
spinel or the rhombohedral ruby — remote, because in this case the magnesia 
is an important constituent of the spinel. A closer analogy is the prevailing 
prismatic habit of the (red) ruby as compared with the pyramidal (blue) 
sapphire ; also aquamarine and emerald crystalline in somewhat different 
habits. On the other hand, variations in composition do not much affect 
the habits of garnet and tourmaline. Speaking at large, it may be said that 
among Kimberley diamonds form depends to a great extent upon colour. 
Thus, octahedra tend to be colourless; yellow diamonds are mostly rounded; 
bright yellow macles are decidedly uncommon, even in mines where yellow 
diamonds abound; ordinary grey bort, when it is symmetrical, is generally 
in cubes and spheres. 
16. Diamond Enclosures. 
Just as foreign crystal inclusions are found in diamonds, so diamonds are 
found embedded in foreign crystals. It is the garnet that is chiefly seen 
associated with the diamond in this wajj. All Kimberley garnets are rolled 
or broken pieces, scarcely ever, if at all, possessing natural crystal faces. 
Generally also, though not invariably, tlie embedded diamond shows signs 
of wear and tear, proving that it must have had a history before the garnet 
formed upon it. Since, then, garnets are found in diamonds and diamonds 
in garnets, it follows that both must have originated in the same era of 
geological time and have crystallised under similar conditions. 
Crystal diamond and bort are also found related to each other in a 
similar way. 
17. Yield. 
The following table, taken from the last Annual Report of the De Beers 
Company, is interesting. It shows the yield in carats per hundred loads of 
the VYesselton and Bultfontein blue : 
Table showing the Yield of Diamonds for Wesselton and Bidtfontein. 
For the 12 months 
Wesselton. 
Bultfontein 
ending June 30th. 
(Carats.) 
(Carats.) 
1898 
27 
1899 
30 
1900 
30 
1901 
30 
1902 
30 
21 
1903 
30 
24 
1904 
28 
29 
1905 
28 
41 
1906 
28 
36 
