Decomposition of Iron Pyrites, 191 



grain shows a portion of a brilliantly polished crystalline face, 

 rarely of two adjacent, the common form appearing to be a cube 

 more or less modified by or passing into the pyritohedron. In- 

 termixed in different specimens with calcite, garnet, chlorite, 

 chalcopyrite, quartz, limonite, etc. Decomposition : a yellow 

 tarnish sometimes occurs, abundant in some specimens, together 

 with particles of reddish iron-ochre. 



No. 61. Pyrite. Franconia, New Hampshire. Brilliant, 

 flattened, yellow and sharply defined cubes of scaley structure, 

 with angles modified by the octahedron and pyritohedron, and 

 sometimes striated, pale brass-yellow and splendent on fracture ; 

 imbedded in a pearly white, glistening, hydromica-schist. Also 

 a similar specimen from Warren, New Hampshire. Decomjjosi- 

 tio7i : commonly a beautiful iridescent tarnish. In some spec- 

 imens, orange-colored iron-oxi(ie surrounds many of the crystals 

 to the distance of 1 or 2 cm., or even stains the entire surface of 

 lamination-seams of the slate with a deep yellowish brown film. 



No. 62. Limonite after pyrite. New Hampshire. Sharply 

 defined, striated, unmodified cubes, pseudomorphous after py- 

 rite, sometimes with an unaltered core of pale brass-yellow and 

 splendent pyrite, and a crust of hard reddish black limonite, 

 with shining iridescent surface ; imbedded in a quartzose chlo- 

 ritic hydromica-schist. 



No. 63. Marcasitic pyrite. Eowe, Massachusetts. A coarse, 

 loosely granular, bright yellow mass, made up of grains which 

 are for the most part imperfect cubes, often highly modifie'd by 

 the pyritohedron, grayish white to yellowish and splendent on 

 fracture. Shining dark blue films, apparently pyrolusite, are 

 common in the interstices. Decomposition : spots of yellow and 

 orange tarnish on many grains. 



No. 64. Pyrite. Eadnor Township, Delaware County, Penn- 

 sylvania. Bright, elongated yellow cubes, highly striated and 

 flattened into very thin rectangular scales, with angles some- 

 times modified by octahedral faces ; pale brass-yellow and splen- 

 dent on fracture ; imbedded in a gray slaty limestone. Decom- 

 position : a rather dull yellowish tarnish and iridescence com- 

 mon. 



No. 65. Marcasitic pyrite. French Creek, Pennsylvania. 

 Bright yellow cubes, with abundant planes of the octahedron and 



