CHAPTER X. 



The Causes of Mineral Evolution. 



Section I. Substance: 



Minerals are composed chiefly of metallic elements, 

 gold, silver, iron, etc. ; hence they are but a visible 

 aggregation of the invisible atoms of the elements. In 

 crystalline substances like ice, salt or sugar, composed 

 of more than one element, a sexual combination of 

 the atoms into molecules of these substances must 

 occur before aggregation takes place. 



Section 2. Structure : 



From the fact that a crushed crystal only reveals 

 lesser crystals of the same design, we assume that the 

 atoms of each element possess a special shape. The 

 ultimate unit of a simple elementary substance is thus 

 a crystalline atom ; and of a compound elementary 

 substance a crystalline molecule. The basis of crystal- 

 line structure is thus a crystal of a special shape for 

 each and every mineral ; and, no matter how large the 

 crystals may be, they are all built up of innumerable 



