Decomposition of Iron Pyrites. 187 



No. 38. Pyrite. Bell Mine, Yavapai County, Arizona. Pale 

 brass-yellow bright grains and tiny crystals, in cavities of a dark 

 mixture of quartz and sphalerite, reported to contain $60 of sil- 

 ver and gold per ton. Polished cubes, sometimes striated or 

 much modified upon the edges by the pyritohedron. Decom- 

 position : a bright orange to deep yellow tarnish on some crys- 

 tals. 



No. 39, Pyrite. Bristol, Connecticut. Sharply defined 

 cubes, pale brass-yellow and brigjit, rarely with octahedral 

 planes or with striation by the pyritohedron upon the solid 

 angles of the hii'gest, and sometimes distorted ; in light gray ar- 

 gillyte. Decomposition : a dull yellowish tarnish. 



No. 40. Linionite, after pyrite. Bristol, Connecticut. Sharp 

 pseudomorphous hepatic cubes in limonite, reddish brown, 

 shining and striated, largely interpenetrated by grains of a soft, 

 brownish yellow, ochreous gangue. 



No. 41. Pyrite. Great Barrington, Massachusetts. Some- 

 what striated cubes, with curved faces by oscillation with the 

 l)yric()hedron, and with sulid angles slightly modified by the 

 octahedroi], and occasional pyritohedra, pale brass-yellow and 

 splendent ; associated with quartz and phlogopite in a blue-gray 

 crystalline dolomyte. Decomposition : after long weathering, a 

 bright blue and yellow iridescence to coppery tarnish ; some- 

 times still bright, when the rock itself is disintegrated, and in 

 part converted to reddish iron-ochre. 



No. 42. Pyi'ite. East Whiteland, Pennsylvania. Sharply de- 

 fined, flattened cubes"like those of No. 8, unmodified, and with 

 traces of striation upon their faces. Decompositio7i : in some 

 cubes, a deep cmst of hepatic alteration into compact limonite 

 of blackish brown color. 



No. 43. Pyrite. Traversella, Piedmont, Italy. Large stri- 

 ated pyi'itobedra, and also cubes with modified angles, pale 

 brass-yellow and splendent, both on the surface and on fracture. 

 Decomposition : in some crystals, films of brownish yellow iron- 

 oxide on inner surfaces of old fracture. 



No. 44. Pyrite. Brockville, Ontario, Canada West. Large 

 unmodified octahedra, and masses with adhering octahedra, pale 

 brass-yellow aiid splendent on fracture. This material has been 

 found to contnin cobalt. Decomposition : dull yellow tarnish on 



