Decomposition of Iron Pyrites. 197 



pale brass-yellow and bright on fracture ; attached to black coal- 

 shale. A few are modified by three-faced pyramids of the tetra- 

 gonal trisoctahedron upon their solid angles. Decomposition: 

 slight dull tarnish, iridescent in places. 



No. 87. Marcasitic pyrite. Pennsylvania. Bright striated 

 cubes, with octahedral and pyritohedral modifications. Some 

 are imbedded in a blackish brown iron-carbonate. Decomposi- 

 tion : a yellow tarnish common. 



No. 88. Marcasitic pyrite. Long Creek Mine, Gaston Coun- 

 ty, North Carolina. Yellowish, coarsely granular and massive ; 

 on fresh fracture, grayish white to silvery white and splendent, 

 and sometimes with the slightest yellowish tinge, by incipient 

 decomposition. A few minute crystals were distinguished in cav- 

 ities, mostly flattened and distorted cubes, modified apparently 

 by the pyritohedron, and a few distorted pyritohedra. Decom- 

 position : a bright orange-yellow iridescence common, and some 

 brownish red limonite-ochre in the interstices, with many beau- 

 tiful films of a bright iridescent blue tarnish. 



No. 89. Marcasitic pyrite. Mooresville, Iredell County, 

 North Carolina. A coarse-grained mass of pyrite, on whose 

 borders unmodified cubes can be occasionally distinguished. 

 Decomposition : much bright red turgite-ochre, in interstices 

 and on seams. 



No. 90. Marcasitic pyrite. Simmond's Mine, Union County, 

 North Carolina. A coarse veinstone, in which unmodified 

 cubes of composite structure occur, pale yellowish white and 

 splendent on fracture. Decomposition : a brass-yellow tarnish. 



No. 91. Pyrite. Magruder Mine, Georgia. Glittering yel- 

 lowish scales and particles, scattered through a white porous 

 <luartz-rock. Some granules appear to be polished unmodified 

 cubes. Decomposition : some red turgite-ochre in the outer 

 surface. 



No. 92. Limonite after pyrite. Buncombe County, North 

 Carolina. Sharply defined unmodified cubes of reddish black 

 limonite, hard and shining on fracture, pseudomorphous after 

 pyrite ; imbedded in a grayish white actinolitic steatyte. A 

 reddish brown film covers the smooth faces of the cubes. 



No. 93. Mahanoy City, Pennsylvania. Large grains and 



