On the Paragenetic Relations of Minerals. 147 



sufficiently indicated by the above-mentioned occurrence of 

 cobalt and nickel in magnetic pyrites. 



However, this formation occurs in true clay-slate, and 

 likewise in mica-slate, gneiss, and granite, although only 

 sporadically. Its occurrence in zechstein and cupreous slate 

 is altogether distinct from its appearance in lodes in the 

 above-mentioned rocks. 



Older Cobalt formation in Chili. — This formation is stated 

 to have been discovered near Huasco in chlorite slate. The 

 Schneeberg cobalt nickel lodes likewise bear axinite, and 

 these two instances of association induced Breithaupt to ex- 

 mine the arsenical pyrites of Thun, sitting upon axinite, 

 for cobalt, which it was found to contain. It would there- 

 fore be advisable to examine pyritic minerals associated 

 with axinite, in order to ascertain whether they contain an 

 available quantity of cobalt and nickel. 



Glaucodot likewise occurs porphyritically in chlorite slate, 

 with precisely the same characters as the mispickel in Frei- 

 berg mines, except that here the adjoining rock is disinte- 

 grated, which is not the case with Chili chlorite slate. 



VI. Tin formation. — The principal representatives of this 

 formation are tin ore (cassiterite) and the two wolframites, 

 ferro- wolframite and mangano-wolframite. These minerals 

 are associated wherever tin ore is worked, and the isolated 

 occurrence of one or other is a great rarity. The scheel- 

 spar is without doubt to be regarded as a product of the de- 

 Composition of wolframite. Beryl and topaz occur together 

 and separately, the former as a very old member of the 

 group. Quartz is never absent. The formation likewise in- 

 cludes such pyritic minerals as contain an essential admix- 

 ture of arsenic, rarely such as are free from that element. 

 Molybdenum glance is a frequent mineral. Calcite and most 

 carbonates, so frequent in other formations, are here very 

 scanty. 



One especial characteristic of this formation is the very 

 limited number of rocks in which its lodes occur. These 

 are — granite, gneiss, mica-slate, and a few clay-slates. Tin 

 and wolfram lodes have never been observed in diorite, dia- 



