GEMS, NATURAL AND ARTIFICIAL 



great brilliancy. As the other portions of the stone 

 remain lusterless and dull the contrast is very marked 

 and the effect very beautiful. 



These star-stones vary in color, although the rays 

 from the star are always the same. When red they are 

 called "star rubies," and when blue, "star-sapphires." 

 Very few, if any, good specimens of these stones are 

 found in the American sapphire regions, Ceylon, 

 Burma, and Kashmir supplying the market. 



The explanation of the appearance of the star in 

 the star-stone lies, of course, in the structure of the 

 crystal. When cut at right angles to the principal 

 axis, peculiar striations and markings parallel to the 

 face of the prism are found. These consist of innu- 

 merable minute cavities, forming three lines which cross 

 one another in the center at an angle of sixty degrees, 

 producing the six-pointed star. 



Only second in importance to the corundum stones 

 if, indeed, they are not quite as important as gems 

 are the beryls, which include the emerald and the 

 aquamarine. Chemically all these stones are prac- 

 tically identical; but here, as in the case of the corun- 

 dum gems, the infinitesimal difference in the color- 

 ing matter makes such an enormous difference in the 

 commercial value of the individual stones. The com- 

 bination of elements that enter into the formation of 

 beryl is: 



Silica 68 . o 



Alumina 18.3 



Glucina 12.2 



Magnesia 0.8 



Soda 0.7 



The color of the emerald is due to the presence of a 



[3 2 3] 



