. 177. OF SURFACE. 



tially differ from those of crystallisation and of cleavage, 

 consists in the circumstance, that generally they preserve no 

 determined direction, and do not produce any regular forms. 

 Here we must except those faces, in which parallel indi- 

 viduals touch one another, or those which depend upon re- 

 gular composition, and which will afterwards be considered 

 more at large (. 179.)- These faces, indeed, preserve a con- 

 stant and determined direction, and are occasionally of a 

 peculiar degree of evenness, although, in other respects, 

 they possess all the properties peculiar to faces of composi- 

 tion. 



Very often the individuals cohere so very strongly in 

 their faces of composition, that they will rather separate 

 in faces of cleavage or of fracture, than in those of compo- 

 sition. If the individuals, on account of their minuteness, 

 withdraw themselves from observation, or become im- 

 palpable, the faces of composition likewise disappear. It is 

 evident, from the preceding observations, that by this pro- 

 cess a compound mineral can never be transformed into a 

 simple one. At all events, we must carefully distinguish 

 between the faces of composition and those of crystallisa- 

 tion and cleavage, the first of which are present in every 

 compound mineral. 



VOL. I. 



