156 Transactions of the Royal Society of South Africa. 
Ex. 2. — A made with one half dodecahedral, the other half inclining to 
octahedral. 
Length of edge, 6*5 mm. 
Thickness, 3'8 mm. 
Ex. 3. — In tli3 case of many Dutoitspan macles the combination plane is 
almost circular in plan even when the faces are flat. 
Ex. 4. — In the case of many Koffyfontein specimens, especially those of 
dodecahedral affinities, the combination plane is isosceles. Others are^ 
scalene. The spread dodecahedral macles from Jagersfontein often show 
the same irregularity. 
The diamonds found in the principal mines of Griqualand West and the 
Orange Free State may be classified for convenience into two holohedral 
groups, namely octahedral and dodecahedral, albeit there is no hard and 
fast demarcation between them. Practically every octahedron carries 
Fig. 4. — A typical large yellow diamond from Dutoitspan. 
dodecahedral striations more or less developed, and nearly all dodecahedra 
show traces of an octahedral lineage ; and this is so even when the 
dodecahedron declines into the tetrahexahedron, as in Fig. 4. From the 
infrequent octahedron on the one hand almost to the cube on the other there 
is an unbroken gradation. There are curious intermediate combinations, in 
which the edges of the rhombic dodecahedron, or tetrahexahedron, invade 
the faces of the octahedron, the said edges existing in embryo side by side 
with the (evanescent) triangular indentations belonging to the octahedron. 
These combinations have been mistaken for triakis- and hexakis-octahedra. 
Of the made the same may be said : There is the same unbroken pro- 
gression from the one group to the other, including the illusory triakis- and 
hexakis-octahedra. 
Generally speaking, swallow-tail corners on macles are a function of 
thickness. The thicker a made relatively to the length of its edges, the 
greater the chance that the twinning plane is truly hexagonal. Otherwise 
the swallow-tails are only seen on macles whose octahedral characteristics 
are the most pronounced. Such macles will then have fourteen more or less- 
