150 On the Paragenetlc Relations of Minerals. 



VIII. Iron spar formation. — There are a great number of 

 lodes whicl i consist solely of iron spar and products of its 

 decomposition. When other minerals occur, it is only in a 

 subordinate manner. The most usual associates of iron 

 spar are quartz and felspar, always older ; heavy spar always 

 more recent. Examples of the paragenetic relation of these 

 minerals are, however, by no means frequent. 



IX. Copper formation. — This includes those associations 

 of the more usual sulphurets, without galena and blende, but 

 generally with iron pyrites. There may be several other 

 groups w T hose relative age is to be determined by future ob- 

 servation. The group here understood is such a one as oc- 

 curs under circumstances similar to those of the clinoedritic 

 lead and zinc formations. The chief representatives of such 

 a group are — copper pyrites predominating, then sulphuret of 

 copper, variegated pyrites, and clinoedrites. Metallic copper 

 is rare, except in lodes, almost always accompanied by red 

 copper, malachite, and other products of decomposition. It is 

 highly probable that such lodes have been formed by the al- 

 teration of sulphurets ; and however much the physiognomy 

 of the individual lodes may vary in respect to the cupreous 

 minerals, they were perhaps originally but little or not at all 

 different. The fine modifications of red copper, malachite, 

 and copper lazure at Chessy, near Lyons, have been proved 

 by Fournet to result from the washings of copper pyrites 

 lodes. The same is probably the case with the immense 

 masses of malachite at Nischne Tagilsk and other parts of 

 Siberia. 



It has been very generally observed, that cupreous mi- 

 nerals containing oxygen occur at the surface or in the up- 

 per parts of the lodes, while at greater depths they consist 

 almost entirely of glance and pyritic minerals. At Bakura- 

 nao, in Cuba, malachite and copper lazure have been found, 

 which, when worked to some depth, were found to cover 

 copper pyrites, cuban and magnetic pyrites. Enormous 

 quantities of malachite, tile ore, copper lazure, and metallic 

 copper are obtained from the mines of Burra Burra, which, 

 when further worked, will most probably be found to yield 

 sulphuretted minerals. The metallic copper may very pro- 



