The Paragenetic Relations of Minerals. 325 



the still more recent iron pyrites. These facts shew that 

 there are uniformities in the association of minerals worthy 

 of being investigated. 



The paragenetic phenomena met with in druses, further 

 indicate that the deposition of some more recent minerals 

 has taken place more readily upon certain of the pre-exist- 

 ing minerals than upon others, as if there had been an un- 

 equal attraction. For instance, in the druses in greisen at 

 the Zinnwald, the tungsten is more frequently implanted 

 upon the smoke quartz than upon the mica. In the lode 

 druses of the Friedrich August mine at Freiberg, the calc 

 spar deposited upon surfaces consisting of iron pyrites and 

 heavy spar, seems to have been attracted more by the latter 

 than the former mineral. In the mine Beschert Gluck 

 pyrargyrite, occurring in druses of galena and polytelite, is 

 found almost only upon the latter. 



The association of minerals likewise seems to determine 

 the form in which one of them appears. The galena occur- 

 ring in druses near Freiberg is, when accompanied by 

 diallogite, always in irregular rounded crystals, calc spar 

 accompanying copper pyrites, probably always presents the 

 most ordinary scalenohedron as the predominating form, and 

 the calc spar upon iron pyrites is invariably in flat rhombo- 

 hedric crystals. 



Another striking circumstance is, that the minerals occur- 

 ring together in a particular district or formation, possess 

 a certain marked physiognomy, so easily recognisable that 

 the localities of hand specimens may be determined by it. 

 The amphiboles, pyroxenes, epidotes, &c. of Arendal, and 

 the same minerals from New York and New Jersey, the 

 older galena and zinc blende formations of Freiberg and 

 those of Cumberland, as well as the minerals occurring in 

 the lodes of Andreasberg (Harz) are sufficient illustrations 

 of these peculiarities. 



Certain associations of minerals belonging to the same 

 genus, sometimes admit of the establishment of specific dif- 

 ferences between them. In a trachytic rock at Laach in 

 Rhenish Prussia, there occur nosean, sodalite, and leucite, 

 imbedded in a porphyritic manner. These three minerals 



