CHAPTER IX. 



The Evolution of Minerals. 



Our chief object in this chapter is to show that a 

 mineral, as composed of magnetic atoms, is itself a 

 magnet, and evolved in all its diverse forms through 

 the agency chiefly of magnetism. 



A mineral is defined as " an organic body possessed 

 of a definite chemical composition, and usually of a 

 regular geometric form." 



All minerals are crystalline, for even amorphous 

 bodies are found to be crystalline under the micro- 

 scope. Hence, as a marked grade of complexity 

 differentiates these crystalline forms, it shall be ad- 

 vantageous for our system to examine them according 

 to the order of their complexity. 



Section I . Simple Geometrical Minerals : 



The forms of crystals, though almost infinite, are 



reducible to thirteen primitive or parent types, of 



which nine are prisms, three octahedra, and one 



dodecahedron. Each mineral usually possesses a 



