CHAPTER I 



THE ROCK-FORMING MINERALS 



Of the simple, undecomposable substances, which chemists call 

 elements, and of which somewhat more than seventy have been 

 identified on the earth, only about twenty enter at all largely into 

 the composition of the earth's crust, 1 so far as this is accessible to 

 examination. It is estimated that 9 7 per cent of the crust is made 

 up of ten elements. 



NONMETALLIC. 





Metallic. 



Oxygen 



. 0. 



Aluminium 



. . Al. 



Hydrogen .... 



. H. 



Potassium . 



. . K. 



Silicon 



. Si. 



Sodium . . 



. . Na. 



Carbon 



. c. 



Calcium . . 



. . Ca. 







Magnesium 



. . Mg. 







Iron . . . 



. . Fe. 



The remaining ten are far less abundant, but yet of considerable 

 importance. 



Chlorine CI. 



Fluorine F. 



Sulphur S. 



Phosphorus . . • . . P. 



Boron B. 



Lithium . . . 



. . Li. 



Barium . . . 



. . Ba. 



Manganese . . 



. . Mn 



Titanium . 



. . Ti. 



Zirconium . 



. . Zr. 



Only two of these elements, carbon and sulphur, are found in a 

 more or less impure state as minerals or rock masses ; the others 



1 By crust of the earth is meant its exterior portion or shell of indefinite thick- 

 ness. It does not necessarily imply any very radical difference from the interior, 

 though the term was first employed to denote the solid external layer which covered 

 a supposed liquid interior. 



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