INTERNAL STRUCTURE OF SOME GOLD CRYSTALS. 145 



These sections show that these simple crystals are by no 

 means equally simple internally, as seen by the light and 

 dark portions of the photograph. The right hand and lower 

 rhombic faces of figure 3 are apparently cut across by the 

 line a, b. This same single face is shown enlarged to 18 

 diameters in Plate XII, figure 1, where it looks almost 

 like two faces of an octahedron; a secondary crystal has 

 been brought out in the etching at A. The dark appear- 

 ance of the right hand half of the rhombic face is due 

 to the way the light is reflected, for both halves presented 

 the same brilliant lustre and colour. The dark lines 1, 2, 4, 

 which look as if made with ink probably indicates a change 

 in the process of growth of the crystal and perhaps of 

 •composition also. The cloudy appearance on the edges is 

 due to the portions of the crystal being necessarily out of 

 focus. 



Figure 1, Plate XII, is a section through a part of the 

 nugget from Tetulpa, South Australia ; externally this 

 appeared to be made up of two conjoined octahedral crystals, 

 but the internal structure is seen to be much more complex. 

 The more or less curved and irregular lines are due to 

 the action of the file, for although they were rubbed out 

 during the process of polishing they reappeared in part on 

 etching: the strain or drag from the action of the file 

 seems to penetrate into the soft gold to some depth, this 

 was also found to occur in other cases, and notably in the 

 section of the ingot of pure gold figured and described in 

 the Journ. Chem. Soc, 1896, and the Journ. Roy. Soc, New 

 South Wales, 1894. 



J— Oct. 2, 1907. 



