Overgrowths on Diamond. 
103 
It is curious that their drawings of crystals 32 and 33 show the protuding 
edges of the lamellae as running nearly parallel with the edges of the rhombs, 
a feature not actually possible in nature. Indeed in this respect their 
version of the aspect of 33 differs absolutely from that of Rose and 
Sadebeck made some forty years earlier, and which they reproduce for 
comparison with their own. 
Boutan also regards these laminated diamonds as macles by hemitrophy. 
He further regards Brewster's celebrated lens of diamond as having been cut 
from a multiple twin of this kind — a remote possibility, maybe, though not 
quite a probability, if only for the reason that a laminated stone is not 
likely to be transparent enough to serve as a good lens. 
One reason against hemitrophy is that one sometimes comes across 
laminated stones which could just as well be called in the French way 
*' macles by penetration," i. e., tending to conform geometrically to the 
interpenetrating twins of the plus and minus tetrahedra ; the lamination 
giving a terraced aspect to the blunt protruding pyramidal bosses very like 
the terraced diamonds from Jagersfontein in miniature. Another reason is 
that lamination is limited to four definite directions each of which is parallel 
to an octahedron face, so that in any laminated stone each multiple-twin set 
intersects another at a constant angle ; and this is the case even when the 
specimen is a made. But macles when they intersect one another are not 
limited to definite directions at all : their seams crossing almost at random 
much as irregularly twinned simple crystals interpenetrate. 
Lamination has an intimate correlation with colour. With very few 
exceptions, all laminated diamonds, no matter where they come from, are 
coloured — brown, mauve, green, or blue-white. Slight lamination may also 
be seen once in a way on poor cape- white diamonds, and on poor yellow 
ones. Eefiexively, nearly every brown, and nearly every mauve, dodeca- 
hedral diamond, either made or simple crystal, whether the tint be light or 
dark, is plainly laminated.* So are most blue-whites when they are of a 
milky transparency or when their tint inclines to mauve. Lamination also 
occurs among the green diamonds from the Eand banket. 
Hitherto I have only succeeded once in seeing signs of lamination in the 
interior of a diamond. This was in an ugly dark-brown brilliant in which 
the lamellae were marked out in alternating lighter and darker brown 
streaks. A fair inference seems to be that a diamond going in general through 
stages of growth and quiescence may, during the latter, become covered with 
colouring matter which is enclosed in a later growth. The apparent uniform 
tint of the final whole stone will be largely a refraction effect (like the grey 
* The featureless brown diamonds of resinous lustre from South-West Africa do 
not show lamination so often as brown diamonds from other sources. For that matter 
South-West African diamonds seldom show any surface detail at all to speak of, 
saving either an exceedingly high polish or a roughening due perhaps to wind erosion. 
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