Decom-position of Iron Pyrites. 183 



fractured surface of the fibrous material remains splendent and 

 untarnished in a cabinet. 



No. 13. Pyrite. AValdenstein, Carinthia. Cubes, slightly 

 striated, pale brass-yellow and splendent ; imbedded in brown- 

 ish black specular hematite. Decomposition : no trace visible in 

 the specimen. 



No. 14. Pyrite. Waldenstein, Carinthia. A specimen like 

 the preceding, covered with pyritoliedra with angles truncated 

 by faces of tlie octahedron. Decomposition : no trace on the 

 outer surfaces, but yellow ochreous films on surfaces of fracture. 



No. 15. Pyrite. Chili, South America. Modified cubes and 

 pyritobedra, pale brass-yellow and splendent; associated with 

 silver ores. Decomposition : traces of blue and yellowish tarnish 

 seen on the faces of some crystals. 



No. 16. Pyrite. Gilpin County, Colorado. Splendent py- 

 ritoliedra, with traces of striation, very pale brass yellow on 

 fracture; implanted on nearly pure massive pyrite. Decompo- 

 sition: a beautiful iridescence and slightly reddish films on 

 some ciystal^ and on fissures. 



No. 17. Pyrite. Pinal County, Arizona Territory. Elon- 

 gated cubes, slightly striated, pale brass-yellow and splendent. 

 Decomposition : no trace visible. 



No. 18. Pyrite. Dognatschka, Hungary. Large cubes, oc- 

 casionally with octahedral modifications upon their solid angles, 

 })a1e brass yellow, with splendent lustre and mirror-like polish, 

 nnd sometimes with slight striation ; dispersed through a gran- 

 ular veinstone of quartz, pyrite, and hematite. Decomposition : 

 a slight iridescence on some ])lanes, or a film of yellow or brown 

 iron oxide, perhaps a mere deposit by vein-waters. 



Concretionary nodule. Linden Mine, Wis. A large concre- 

 tionary nodule, consisting of three materials ; a finely fibrous 

 centre, a cellular crust made up of radial grains, and an outer 

 layer of cubes ; associated with sphalerite. 



No. 19. (Fibrous core). Pyrite. Finely fibrous and radi- 

 ating from the centre of the nodule, pale brass j^ellow and splen- 

 dent, identical in appearance with No. 1. Decomposition: a 

 bronze-colored tarnish on ordinary exposure. 



No. 20. (Cellular layer), marcasitic pyrite and marcasite. 



