Gubelin, E.. <br/><br/>
Internal World of Gemstones: Documents from Space and Time /  

 - Second Ed. /  
 - London WC2B 6AB :   Butterworth & Co. Ltd. ,   1979 
 - p.234 :  
<br/><br/><label>ISBN: </label>0-408-00436-3 
<br/><br/><label>Dewey Class. No.: </label>H19  / L9