Decow position of Iron Pyrites. 403 



of emu were implanted or encrusted upon the other. Wohler 

 came to the same conclusion of the simultaneous formation of 

 the two minerals. 



Zippe 89 has discovered pseudomorphs of mixed pyrite and mar- 

 casite, after red and black silver ore, at Joachimsthal, in Bohe- 

 mia, in which " sometimes the same pseudomorphs consist partly 

 of iron pyrites and partly of radiated pyrites ;" the same associ- 

 ation was observed by A. Stelzner in pseudomorphs after silver- 

 glance, near Brand, in Saxony. 83 



Displacement pseudomorphs also occur among these three 

 forms of iron pyrites : 



Marcasite after py rite, in cubes which are paramorphs, in plas- 

 tic clays of Liebnitz, Bohemia, 84 and near Freiberg. 85 



Marcasite after pyrrhotite, in hexagonal prisms, near Freiberg, 

 Stranitza, Dognatzka, etc., 86 and at Loben near St. Leonhard in 

 Carinthia. 87 



Pyrite after marcasite, as a paramorph, at Rodna, 88 Transyl- 

 vania, in the form of the well known double twin crystal of the 

 latter mineral, but made up of an aggregate of minute cubes and 

 pentagonal dodecahedra of the former. 



Pyrite after pyrrhotite,, near Freiberg, 89 Himmelsfiirst, Wun- 

 siedel, etc. 



It is significant that in no case has pyrrhotite ever been found 

 as a pseudomorph after either of the other two pyrites. 



Our view of the part constantly played by the iron pyrites, in 

 isomorphous replacement, yet needs a brief reference to their ar- 

 rangement in the complex constitution of many other metallic 

 sulphides, as shown by Rammelsberg and Dana. In the table 

 below, some of the more simple and prominent are gathered to- 

 gether ; but the intermediate proportions, either of mere mechan- 



83 Blum, op. cit. (1843), 300-304. 



83 Berg. u. Hiitt. Zeit., XXVIII, No. 10, 83. 



84 Blum, op. cit., Nachtrag (1847), 149-151. 

 s5 Roth, op. cit., I, 110. 



86 Tdem, 242. 



S7 J. Rumpf, Verk. d. K. K. geol. Reichs. (1870), No. 1, 2-3. 



88 Sillem, Jahrb. f. Min. (1851), 399. 



s9 Paragenesis, Breilhaupt, 130. 



