PASSAGE OF ONE FORM INTO ANOTHER. 



55 



That of its lateral edges, or superior edges, (Fig. 110,) by two 

 planes, results in a Dodecahedron with scalene triangular faces, 

 Fig. 131. 



Fig. 130. 



Fig. 131. 



The second Rhomboid of a mineral, or the first new one, may 

 itself suffer the same modification as the primary, and thus produce 

 another, still more obtuse. Carbonate of Lime presents us, in this 

 way, with four distinct Rhomboids. 



Though it may appear to the student hardly possible that the 

 changes to which the primary forms are subject, are as numerous 

 as would appear from the instances enumerated, yet he will find 

 them in reality to be much more so, as his knowledge of crystals 

 becomes extended. Still, those which have just been pointed out, 

 are among those most frequently met with, and the most easily un- 

 derstood by the young student. 



It will now be seen, that it is natural that most crystallized miner- 

 als should present themselves under several distinct forms, (. 30,) 

 since this variation of form is a necessary result of the symmetry of 

 structure in one primitive form, and of the laws no less symmetrical 

 to which these modifications are subject. At the same time, it must 

 be recollected, that the number and the nature of these various forms 

 of the same substance are necessarily limited, and dependant upon 

 the structure of one fundamental form. (. 31.) 



