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Transactions of the Boyal Society of South Africa. 
market sense, are the occasional irregular crystals upon whose surfaces 
thick coatings of a kind of grey bort have been deposited. This bort might 
to all appearance have been put on in the form of a wet paste, with a 
spatula, and then dried hard. Such specimens as have come to light have 
never been completely covered by the bort, although there are pieces of the 
bort which look as if they may have diamond within. This kind of bort 
overgrowth is not commonly found on a natural crystal face, but rather 
on what appear to be faces of arrested growth, say on surfaces of attach- 
ment, and may be material which has flowed into and filled the interstices 
between the diamonds of a cluster, at any rate it simulates that effect. A 
Dutoitspan flat diamond which was found recently had such a surface of 
attachment covered with bort, and on the surface of the bort, which was 
much pitted, there were numerous tiny black particles — whether of graphite 
or of amorphous black diamond could not be determined — filling the pits. 
The bort overgrowth here spoken of forms a link between common grey bort 
and the cement-like stuff of the next section, merging by insensible grada- 
tions from the one into the other. 
Fig. 2. — Hailstone structure of diamond. Surface of fracture showing 
alternate shells of diamond and grey cement. 
The Hailstone Structure. 
[Jnequivocal proof that the crystallisation of diamond is by no means 
necessarily a rapid and continuous process is supplied by the diamonds 
which in a previous paper have been likened to hailstones.* Such 
diamonds are common enough, although they do not seem to have attracted 
much attention. Typically they consist of what looks like a kind of 
hardened and more or less porous paste, superficially not unlike Portland 
cement, alternating with layers or shells generally of curvilinear section (as 
sketched in Fig. 2) of clouded crystal diamond. Sometimes the core is 
diamond ; now and then it is diamond with a small central spot of some 
cognate material ; often it is an irregular lump of the cement alone so far 
as one can judge of its interior without breaking it open. When the outer- 
most layer is cement the specimen is shapeless ; when it is diamond it tends 
to a diamond contour — cube, octahedron, or dodecahedron — and it is usually 
* " Some Controversial Notes on the Diamond," ' Trans. E.S.S.A./ 1920, viii, p. 129. 
