CATALOGUE OF GEMS. 



537 



III. COMPARATIVE TABLES OF THE COLORS AND DISTINGUISHING 

 CHARACTERS OF THE BETTER-KNOWN GEMS. 



I.— LIMPID OR COLORLESS STONES. 



Zircon (jar- 

 goon). 



Specific 

 gravity. 



Sapphire 



Spinel 



Topaz 



Diamond 3. 48 -3. .52 



3. 916-4. 27 



3.5 -3.8 



Tourmaline 



Bervl . 



Quartz (r o c k 2.5.5 -2. 

 cry.-ital). , 



7.5. Will just 

 scratch quartz. 



Refraction and 



refractive 



index. 



Disper- 

 sion. 



9. Scratched by 

 diamond; will 

 .scratch all oth- 

 ers of the class. 



8. Scratched by 

 sapphire; will 

 scratch (luartz 

 easily. 



. Scratched by 

 .siipphire: will 

 scratch quartz 

 easily. 



10. Scratches all 

 other stones. 



7-7.5. Willbarely 

 scratch quartz. 



Double. 1.990. 



Double, but 

 not strong. 

 1.76.5. 



Single. 1.755 

 to 1.810. 



Double. 1.635. .025 



Single. 2.4.55.. 

 Double. 1.625. 



7.5-8. Specimens Double; weak. 



vary. Scratch- | 1.585. 



cd by .spinel; ] 



scratches 



quartz. 

 7. Scratches glass. Double. 1.519. 



.38 



. 028 



Distinguished from dia- 

 mond, which it resem- 

 bles, by its hardness and 

 specific gravity and by 

 the fact that strong hy- 

 drochloric acid dropped 

 upon a polished face 

 will, upon removal, 

 ' liavedestroyedordulled 

 its brilliancy. The acid 

 is without effect on the 

 diamond. The zircon 

 acquires -|- electricity 

 by friction. 



Distinguished by its hard- 

 ncssand specificgravity. 

 Becomes electrified by 

 friction. 



Distinguished from other 

 members of the group, 

 except topaz, by its spe- 

 cific gravity and hard- 

 ness, and from topaz by 

 not possessing pyro- 

 electricity. 



Becomes electrified by 

 friction and heat. Dis- 

 tinguished from all 

 stones in the group, ex- 

 cept spinel, by its spe- 

 cific gravity and hard- 

 ness, and from spinei 

 by its electrical prop- 

 erties. 



Readily distinguished by 

 its hardness. 



Becomes + and — electri- 

 fied by heat or friction; 

 one portion of a crystal 

 attracts and another 

 repels light bodies. 



Specimens may become 

 electrified bv friction. 



