LITHOLOGY. 95 



Scratch with ease and effervesce slowly, it consists of 

 Magnesite or Dolomite. 



Scratch with ease and effervesce not at all, it consists 

 of Sulphates or Silicates. 



Scratch with difficulty and effervesce not at all f it 

 consists of Silicates. 



Scratch not at all and effervesce not at all, it is a 

 pure Silicate when crystalline, and Siliceous when 

 compact. 



Scratch not at all and effervesce slowly, it is calca- 

 reous Sandstone when granular. 



Actual determination at home of the hardness of a 

 mineral is made by comparison of the specimen with 

 others of which it is known, the scale arranged by Moll 

 being the one generally adopted. 



HARDNESS. 



( 1. Talc. 

 Scratched by the nail. rt _. , ,. 



I 2. Eock-Salt. 



, ( 3. Gale-Spar. 



Scratched by the knife with 1 A ^ 



J < 4. Fluor-Spar. 



ease. i K . ... 



V. 5. Apatite. 



Scratched by the knife with ) , 



difficulty. | 6 ' Felspar ( rthoclase )- 



/ 7. Quartz. 

 Cannot be scratched byj 8. Topaz. 



knife or file. "1 9. Sapphire. d^^^Ju^ 



\ 10. Diamond. 



The test is made by " rubbing the specimen over a 

 tolerably fine-cut file, and noting the amount of powder, 

 and the degree of noise produced by so doing. The less 

 the powder and the greater the noise the harder will 

 be the mineral. On the other hand, a soft mineral will 



