Dcco}npositioii of Iron Pyrites. 185 



licdron. A little soft reddish tui-gite-oclire lies in the inter- 

 stices of the crystals. Locality, 120th street and 10th avenue. 



No. 25. Pyrite. Hazelgreen, Wisconsin. Glittering drosy 

 crusts and films, pale yellowish and brilliant on fracture, lining 

 seams and cavities in a gray limestone. The crystals over these 

 surfaces are all octahedra, in part composite and made np of tri- 

 angular scales. Decomposition : a bright brass-yellow tarnish, 

 partly bronze-colored and iridescent. 



No. 20. Pyrite. French Ci-eek, near Pottstown, Cliester 

 County, Pennsyl' ;inia. Liglit brass-yellow and splendent cubes, 

 smooth or wit traces of striation ])i-oduced by oscillation with 

 1 lie octahedron : zonal lines of striae around some faces. The 

 cubes a]-e mostly intergrown with each other, and with smaller 

 cubes implanted. From a calcite-vein. Decomposition : slight 

 iridescent stains on some crystals. 



Xo. 2v. Pyrite. Falls of French Cri^ek, Pennsylvania. 

 IJrilliant, pale, brass-yellow octahedra, with composite faces, 

 mostly unmodified, but in some crystals with the solid angles 

 bevelled or rounded oil by planes of the pyritohedron. Associ- 

 ated with byssolite, in calcite. Decomposition : brilliant irides- 

 cent tarnish and crusts common, colored deep yellow, blue and 

 red. 



No. 28. Pyrite. Negaunee, Mich. A brilliant group of 

 cubes highly modified by the hemi-teti-ahexahedron, etc., joale 

 brass-yellow and splendent on fracture, occupying a geode in a 

 quartzose reddish brown hematite. Decomposition : a slightly 

 iridescent, blue tarnish. 



No. 29. Pyrite. Tuckalioe, Westchester County, New York. 

 Brilliant yellow irregular granules, looking like chalcopyrite but 

 hard ; in white dolomyte-marble. Some grains show the form 

 of cubes, with solid angles modified by the octahedron. Decom- 

 position: no trace except a brilliant blue and red iridescent tar- 

 nish. 



No. 30. Pyrite. Rio Marina, Elba. Bright, pale brass-yel- 

 low grains and cubes, striated and ^vith solid angles occasionally 

 modified by the octahedron ; scattered through cellular black 

 hematite. Decomposition : no trace visible in the specimen ; 

 but the surfaces of fracture become bronze-colored, on exposure 

 to dry air for several weeks. 



