436 ATOMIC CONSTITUTION AND CRYSTALLINE FORM 



individualize these — so long must the physical nature of the mineral 

 embodiment claim to be considered, and to be considered prominently, 

 in the classification. The time is now altogether departed when cal- 

 cite and iron-spar, for example, were held to be less nearly related 

 than calcite and arragonite. 



But if this truth be now almost universally admitted, there seems 

 to be a strong tendency in its application to make all characters sub- 

 servient to two : atomic constitution on the one hand, and crystalline 

 form on the other ; and to force these into corelation, by the assump- 

 tion of various arbitrary and scarcely consistent principles. I do not, 

 of course, intend to deny the high value of these characters, considered 

 generally ; but I feel warranted in asserting that, by their arbitrary 

 employment, to the exclusion of other considerations, many really 

 unphilosophical groupings are so concealed under an apparently philo- 

 sophical garb, as seriously to retard the proper progress of tbc science. 



That mere agreement of crystalline form — even in minute angular 

 measurements, planes of composition, &c. — is really in mpny instances 

 of no greater value as a classification-character than similarity of hard- 

 ness or lustre, is necessarily forced upon us, to cite but a single case, 

 by the crystalline identity of borax with augite. That the identity in 

 question may be explained, perhaps, not only here but in other cases, 

 by reference to atomic volume, does not in any way invalidate our 

 argument. Borax and augite, alike in crystalline form, are, when 

 viewed as minerals, when considered in their entire relations, altogether 

 dissimilar. Hence, if two minerals happen to exhibit the same forms 

 and combinations, with corresponding angles, &c, they are not solely 

 on that account to be placed in the same classification group, because, 

 as shewn in the example just referred to, in all their other relations — 

 their essential mineral relations — they may stand most widely apart. 



Atomic constitution, on the other hand — even if we shut our eyes to 

 the fact of its arbitrary and unsettled character — is of no greater 

 value. Minerals may be assumed to possess, wholly or in part, the 

 same atomic constitution, and yet be utterly opposed in habitus, in 

 conditions of occurrence, in all in fact that constitutes their mineral 

 embodiment. Subdivisions, consequently, founded on this principle, 

 become most artificial. Iron pyrites, for example, is commonly con- 

 sidered to be represented by the formula FeS 2 , whilst in magnetic 

 pyrites and in copper pyrites we have, as one of the constituents, the 

 compound Fe 2 S 3 . A sesqrd-sulphide (Sb 2 S 3 or As 2 S 3 ) is also pre- 

 sent (according to the received opinion) in the red silvers, zinkenite, 

 &c. ; but who will for a moment maintain that copper pyrites (to say 

 nothing of magnetic pyrites) is not more closely related, in every 



