Pi'of. Naumann on Mineralogical Classification. 31 



start with the question, Wliat idea is to be regarded as the 

 actual guiding principle of that intellectual operation, whose 

 result we term a mineralogical system 1 Now, as the idea 

 of identity is exhausted in the determination of species, it is 

 only the idea of resemblance which can form our proper guide 

 in all operations of classification. 



The resemblance, however, of two things, is their gi^eater 

 or less agreement in certain prominent characters ; and it 

 can neither be founded on all their characters, nor on their 

 complete agi'eement, because, otherwise, it would coincide 

 with the idea of identity. It must rather be regarded as, in 

 its very nature, somewhat fluctuating, and susceptible of 

 various gradations ; it is recognizable sometimes in one, and 

 sometimes in another character, sometimes in a higher, and 

 sometimes in a lower degree. 



Hence it results that, in every classification founded on 

 the idea of resemblance, we must commence with the inves- 

 tigation, — What are the essential characters in which resem- 

 blance is especially to be sought for and regarded ? Or, in other 

 woi'ds, and with particular reference to the question now be- 

 fore us, What value is to be assigned to the various proper- 

 ties of minerals, as regards the requirements of a systematic 

 arrangement \ In answering this question, we arrive at the 

 result, that it is the resemblance of inorganic masses, without 

 reference to their form, which must especially be kept in 

 view in mineralogical classification. 



Morphological properties. — In establishing species, mor- 

 phological properties occupy the first rank ; for amorphous 

 and crystalline minerals can never be united in one and the 

 game species, and in crystalline minerals, relative identity 

 of crystallogi-aphic form, that is to say, the belonging to the 

 forms of one and the same crystallographic series, with a 

 similar character in the combinations, is to be considered as 

 the first requisite of specific identity. It is entirely difi'erent, 

 however, with the systematic arrangement of species. Calca- 

 reous spar and arragonite, a rhombohedral and a rhombic 

 species, approach each other so nearly, that, in a mineralo- 

 gical system, they must follow each other as closely as pos- 

 sible. The same is the case with the three species of ii'on 



