The Paragenetic Relations of Minerals. 105 



the green varieties called pistacite, are probably more fre- 

 quent in lodes than in rocks. It is likewise remarkable, that 

 some anhydrous silicates which occur in the form of lodes are 

 never met with as constituents of rocks. Among these are 

 axinite (strictly speaking, a silico-borate), the very rare mi- 

 neral zygadite. The former has been found forming a lode, 

 together with an arsenical pyrites, rich in cobalt, cobalt 

 glance, &c, in Chili, Saxony, and Sweden. 



The other anhydrous silicates occurring in lodes are, 



some garnets, pyroxenes, amphiboles, titanites, lievrite, epi- 

 dote, beryl, and topaz. 



Certain hydrated silicates are more frequent ; for instance, 

 phrenite, datolite (a silico-borate) ; most of the zeolites, many 

 of which occur likewise in vesicular cavities ; some micas, 

 and a few amorphous mineral substances. 



Silico-borates certainly never occur as constituents of rocks. 

 Datolite is the only one which occurs in vesicular cavities. 



The chief part of the mineral species which occur in lodes 

 comprises such as are unknown as constituents of rocks, and 

 they consist, moreover, of chemical elements which are not 

 present in rocks. These remarkable and important facts un- 

 questionably indicate: 1. That the minerals contained in 

 lodes have not been formed by the extraction of the adjoining 

 rock ; 2. That such substances are chiefly present in veins, 

 which, at the time of the formation of the rocks, were re- 

 tained in the interior of the earth. We are unacquainted 

 with any rocks from which it is probable that the sometimes 

 enormous lodes of lead, silver, copper, antimony, zinc, arse- 

 nic, bismuth, cobalt, and nickel minerals, or even those of 

 iron or barium, and the sulphur of the sulphurets, could have 

 been derived by such a process of extraction by water. In- 

 deed, heavy spar occurs in the Erzgebirge in such frequent 

 and large veins that it may constitute no inconsiderable part 

 I of the entire mountain range, while we are unacquainted 

 with any single mineral in these rocks, which are generallv 

 in an undecomposed state, containing baryta. Admitting the 

 hypothesis of an original chaotic admixture of the elements 

 it may be conjectured that the alkaline minerals were first 

 formed, on account of the more ready oxidation of their 



