32 Pi'of. Xaumann on Mineralugical Classification. 



pyi'ites. with vesuviaii and garnet, and with rutile and Brookite. 

 although these substances are separated from each other by 

 their entirely different crystallographic systems. "We thus 

 arrive at the conclusion, that great difference in morphologi- 

 cal properties may be united with great resemblance of the 

 mass; a result which is strikingly evident in most dimorphous 

 substances. 



On the other hand, a glance at mineralogical arrange- 

 ments formed according to crystallogi-aphic systems, teaches 

 us, that great resemblance, and even identity, in morpholo- 

 gical properties, may exist along with the most remarkable 

 difference in the mass. Hence it evidently results, that mor- 

 phological properties can only receive a subordinate degi'ee 

 of attention in a mineralogical systematic arrangement ; and 

 that although the distinction of the amorphous and crystal- 

 line nature of the substance be attended to, yet that scarcely 

 any importance is to be assigned to the distinction of crystal- 

 lographic systems. Mineral systems, founded on crystallo- 

 graphic forms, have, in fact, only a crystallographic but no 

 physiographical interest ; because such systems sometimes 

 brino; together the most dissimilar substances, and at other 

 times place the most similar minerals far apart. When 

 similar masses also exhibit similar forms, the matter is much 

 facilitated, and the gi*oups to which they belong are rendered 

 much more distinct by such an agreement. This is the case, 

 for example, with the felspar group, and with the hornblende 

 and augite group. 



As, therefore, in a classification of mineral species, the mor- 

 phological properties perform only a very subordinate part, it 

 is self-evident that those physical properties which are direct- 

 ly connected with, and dependent on, the crystallographic 

 form, must receive just as little consideration ; this is espe- 

 cially the case in regard to cleavage, the refraction and po- 

 larization of light, &c. ; and thus, while cleavage is a cha- 

 racter of first-rate importance for specification, it is of but 

 small moment for classification. If, for example, we attempt 

 to unite all the mineral species having a very perfect monoto- 

 mus cleavage, as, indeed, has been partly done, we shall find 

 the most dissimilar minerals placed together in one order, 



