different crystalline substances, a thorough knowledge of 

 this being an essential part of the mental equipment of 

 the expert. The mere matter of color, which is of such 

 importance in determining the market value of a gem, 

 is hardly considered at all in determining its identity, 

 at least until several other tests have been made. 



Another important means of identification is the 

 test for hardness. The diamond, of course, heads 

 the list for resisting attrition, while the sphene is at the 

 very bottom, with the other gems ranging in between 

 at definitely determined intervals. The mineralogist 

 Mohs drew up a scale of hardness many years ago, of 

 which the following is a universally accepted modi- 

 fication : 



Diamond 10. o Alamandine Garnet 7.3 



Sapphire 9.0 Essonite 7.0 



Ruby 8.5 Amethyst 7.0 



Chrysoberyl 8.5 Kunzite 6.5 



Spinel 8.0 Peridot 6.4 



Beryl 8.0 Adularia 6.3 



Topaz 8.0 Green Garnet 6.0 



Jargoon 7 . 5 to 8 . o Opal 6.0 



Emerald 7.5 Turquoise 6.0 



Tourmaline 7.5 Sphene 5.0 



Phenakite 7.5 



Mohs' original scale was : 



Diamond 10 Apatite 5 



Sapphire 9 Fluorspar 4 



Topaz 8 Calcite 3 



Rock Crystal 7 Rock Salt 2 



Felspar 6 Talc i 



The test for hardness is made by endeavoring to 

 scratch the doubtful gem with each substance of the 

 scale, until one is found that will neither scratch nor 

 be scratched by it. The stone will then be proved to 

 be of the same hardness as the test-stone, and a defi- 

 nite step in the identification is accomplished. 



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