158 Transactions of the Royal Society of South Africa. 
Among diamonds the macle-forming tendency does not appear to be 
strong, though some mines have it more than others. Some test-countings 
gave the following proportions by weight which macles bear to the total 
yield : 
Bultfontein . . about 1 per cent. 
Wesselton . . ,,1^ „ 
Dutoitspan . . at least 3 ,, 
De Beers and Kimberley 5 
The low percentage shown by Bultfontein is remarkable, that being the 
mine above all others where groups and clusters of diamonds abound, and 
where irregular twinning is so prominent a feature as to be almost a 
nuisance to the diamond merchant. The above percentages suggest, though 
they may not prove, that where regular twinning is most in evidence there 
irregular twinning will be least. 
The most striking peculiarity of the diamond made is of course its 
prevailing tabular habit. Un twinned crystals are pretty often flattish, and 
now and then, particularly at Bultfontein, tabular octahedra — the " portrait 
stones "* of the diamond market — are met with. These, saving that they 
-are nearly always elongated, are equivalent to octahedra from which opposite 
facial blocks have been cleaved off, so that they have hexagonal faces. 
Measurements of four of these Bultfontein portrait stones gave the following 
"dimensions : 
Length. 
Breadth. Thickness. 
1. 110 
6-0 
2*5 mm. 
2. 6-9 
40 
1-8 „ 
3. 97 
? 
2-3 „ 
4. 77 
? 
2-2 „ 
As articles of merchandise they are 
m.uch to be preferred to macles, but 
iheir philosophical interest is incomparably less. Superficially the chief 
differences between tabular crystals and macles are : 
(1) The triangular indentations of the two opposite faces of a tabular 
crystal are oriented in opposition from any one point of view, whereas 
those of the made are oriented the same way. This difference is very 
pleasingly shown if the crystal and the made are held up to the light, side 
by side. 
(2) The crystal breaks normally, the made symmetrically. 
(3) The crystal is glassy with a shining lustre, the made not charac- 
teristically so. 
(4) The made is peculiarly tabular, the tabular crystal is rare. 
The last clause is perhaps the most important. The ordinary crystal is 
by preference a regular solid whose axes are equal in length. And it seemed 
worth while to attempt to determine whether there is a standard of dimen- 
* So called because they serve as glazing for small miniatures. 
