175 



As further evidence of this st''iieture I And that in the case of a 

 cabochou cut (smooth, convex upper surface) I'uby which I myself cut 

 from a fragment of a boule, I can plainly see a six-pointed star when 

 viewed in direct sunlight or even when seen by tlie light of a single candle. 

 This star effect is due to the presence in the material of microscopic bub- 

 bles, which produce somewhat the same effect as is produced by dust 



Vi eujed. oo f^Lot side • 



particles in a beam of light crossing a darkened room. The six-pointed 

 character of the star plainly indicates that the material has the hexagonal 

 arrangement, as a tetragonal crystal under similar conditions would pro- 

 duce a cross rather than a six-pointed star. 



