The Great Diamond from the Transvaal. ' 171 



projection depicted in the Text-figure, whicli has been drawn in the 

 Mineralogical Laboratory of the Oxford University Museum, by the 

 kind permission of Prof. Miers, F.R.S. The drawing is to half scale. 



Description of the Surfaces. 



A is an original octahedral face showing typical striations, the 

 bands varying from 0"1 to 0'4: centimetre, and running parallel to 

 the edge A-E. 



B is a large surface slightly curved showing partial striations, 

 which, however, are interrupted by the slightly mammillary character 

 of the surface. 



C is also a natural surface showing a few striations parallel to 

 the edge C-E. 



D. Between B and F, C, G, there is an irregular octahedral 

 face D, showing distinct equilateral triangular indentations which 

 resemble etched figures, except in regard to their comparatively large 

 size, the largest having a side measuring 0*7 centimetre. D is 

 parallel to E. 



E, F, G, H, are cleavage planes. 



E is the largest of these, and is a very perfect cleavage plane. 

 Parallel to it within the crystal there is a small air layer between 

 two internal cleavages, producing a ' rainbow ' or Newton's rings. 



F is the second largest of the cleavage planes and shows a small 

 spot within the crystal. 



G is an irregularly shaped cleavage plane. 



H is another cleavage face showing series of cleavages in the 

 corner bounded by E and G. Two spots are visible, one actually on 

 the surface, the other about 1 cm. within the crystal. 



Of the faces given, A and G, H and B, and E and D are parallel. 

 In the case of B and H the parallelism is imperfect owing to the 

 curvature of B. 



The purity of the crystal is best seen on looking into face E, and 

 the lustre is well seen on the irregular natural face B, the broken 

 cleavage on H causing a good deal of refraction which affects B to 

 some extent as the facets of a cut gem would. For a large stone 

 the crystal is of remarkable purity, and the colour approximates to 

 that of a blue- white. 



The large size of the cleavage planes E and F indicates that 

 a very considerable portion of the crystal is wanting. From the 

 shape of B, D, and G, one can say that the entire crystal was 

 irregular in shape, but A and D being octahedral faces, the pre- 

 sumption is that the complete crystal was a distorted octahedron, 

 probably with dodecahedral faces developed on the edges. The 

 portions missing probably amount to more than half of the original 

 crystal. 



The Cullinan diamond, as it has been named, after the Chairman 

 of the Premier Company, is more than three times the weight of 

 the largest diamond previously known — the famous stone found in 

 1893 at Jagersfontein in the Orange River Colony, which weighed 

 972 carats. 



