192 0. .1. Derby- Ifotabh Brazilian Diamond. 



one of the pieces in such a way as to produce an obtuse ridge 

 extending diagonally across the curved face from end to end, 

 hut without distorting, except in shape, the two plane faces. 

 The accompanying figures, all of natural size, represent very 

 accurately, in Nos. 1 and 2, the two plane faces; but, owing to 

 light effects, the curved faces shown in Nos. 3 and 4 present 

 an appearance of being made up of subordinate faces (sugges- 



FlG. l. 



Fig. 2. 



Fig. 3. 



Fig. 4. 



tive of distorted dodecahedral crystallographic planes) that do 

 not appear on the stone itself. 



Greatest length 38 mm 



" width 22 mm 



" height 23 mm 



As is well shown in these figures, all the faces, both plane 

 and curved, are covered by sharp-cut lines and depressions 

 similar to those produced by etching, though in this case it 

 seems much more probable that they are features of crystal- 

 line growth. The large semi-circular depression in the middle 

 of the base line of fig. 1 is, however, an artificial fracture due 

 to a blow that raised a thin scale along a plane of octahedral 

 cleavage characteristic of the mineral. The small cleavage 



