60 TERMINOLOGY. 



All crystals which have hitherto been discovered, are capable of be- 

 ing referred to some one of the primary forms which have been de- 

 scribed. Should a crystal be hereafter discovered, which agreea- 

 ble to the symmetrical laws of derivation could not be referred to 

 one of these, a new primary form would be necessary, and it would 

 constitute a member of a new system of crystallization. In each of 

 these systems it is customary to consider all those forms as belong- 

 ing to it, which are geometrically derivable from it, although they 

 should not as yet have been observed among minerals. 



In the system of crystallization, the dimensions are not fixed, ex- 

 cept indeed where it is so from the nature of the fundamental form as 

 in the regular Octahedron, the Cube, the Tetrahedron and the rhom- 

 bic Dodecahedron. Any number of prisms, whatever may be their 

 height, will belong to the same system of crystallization ; any num- 

 ber of Rhomboids, whether acute or obtuse, will be included under 

 the same system, &c. 



The system of crystallization derived from the different primary 

 forms are termed the systems of those forms respectively : thus the 

 system of crystallization belonging to the Cube, &c. 



. 56. SERIES OF CRYSTALLIZATION. 



The primary form being supposed to possess determined 

 dimensions, the assemblage of derived forms becomes a 

 series of crystallization. 



Among the primary forms the Tetrahedron, the Cube, the regular 

 Octahedron and the rhombic Dodecahedron possess invariable dimen- 

 sions ; accordingly they will each possess but one series of crystalli- 

 zation, while the other systems of crystallization as they possess va- 

 riable dimensions will comprehend an unlimited number of such 

 series, or as many as there may be differences in the dimensions of 

 their primary forms. Thus in the system of crystallization belong- 

 ing to the right square Prism, there may be any number of series of 

 crystallization according as these prisms may be conceived to differ 

 from each other in the relation of their respective heights to the 

 length of the edge of their square base. The system of rectangu- 

 lar Prisms may contain many series according to the particular prisms 

 which vary from each other in the relative dimensions of their 

 planes. The individuals of the system belonging to right rhombic 



