0. A. Derby — Notable Brazilian Diamond. 193 



face thus produced is parallel to the main face and to several 

 subordinate platform-like faces that rise above its general sur- 

 face. The face shown in fig. 2 also shows, with still greater 

 distinctness, several parallel platforms as well as a sharply 

 defined pit with coarsely ridged walls, suggestive of an external 

 mould of the point of an octahedral diamond crystal of the size 

 of about a carat. 



According to the description and figures given by Dufrenoy* 

 the Star of the South was in the rough a semi-ellipse and 

 thus strikingly similar in general form to the present stone.f 

 It is also on record that the original form of the Dresden stone 

 was such that it suggested the hypothesis that it and the Star 

 of the South were cleavage fragments of an original elliptical 

 (distorted dodecahedral) unit. It is thus highly probable that 

 the three stones, representing a limited area of diamond-bear- 

 ing ground, were characterized by a quite similar original 

 shape, that is to say, a vaguely defined combination of curved 

 faces constituting a dome rising from a plane face. In the 

 case of the stone here noted a considerable portion of the 

 ideal dome is cut away by a second plane face, and judging 

 from No. 2 of Dufrenoy's figures, this was also the case with 

 the Star of the South. Without entering into crystallographic 

 considerations, a comparison may be suggested with fig. 7, pi. 1, 

 of Rose and Sadebeck's memoir on the crystallization of the 

 diamond,:}: which represents a dome-shaped diamond with 

 a flat base which is interpreted as a case of hemimorphism. 



An interesting question, which must, however, be left to 

 crystallographers, arises as to the significance to be given to the 

 plane faces and to the surface markings of this diamond. The 

 first and most natural impression is that the plane faces are 

 cleavage planes, and the fact that a small artificial fracture 

 shows that one of them is strictly parallel to an octahedral 

 cleavage seems to confirm this view. In this case, however, 

 they represent a superinduced feature, and the superficial 

 markings on them must also be posterior to the formation of 

 the crystal and thus can only be attributed to etching ; a 

 process which is difficultly conceivable in the case of the 

 diamond. If, on the other hand, the markings are an original 

 (growth) feature, the plane faces must also be original, since 

 the markings on them must have been produced at the same 

 time as on the curved faces. In the Star of the South, which 



* Traite de mineralogie, 2d ed., vol. 2, p. 95, pi. 225, figs. 1, 2 et 3. 



f It is to be strongly suspected that the sharply defined dodecahedral 

 faces shown in Dufrenoy's figures 1 and 2 are the crystallographer's inter- 

 pretation of such obscure indications of crystalline faces as are seen on our 

 figures 2 and 3, and thus might receive a materially different interpretation 

 from another observer. 



X Abh. d. K. Akad. d. Wissensch. in Berlin 1876. 



