198 Decomposition of Iron Pyrites. 



cubes, with faces often very finely striated, and cracked up by 

 cubical aggregations, cellular and largely interpenetrated by 

 the matrix, pale yellowish white and bright on fracture ; in 

 blackish gray carbonaceous shale. Decomposition : rather dull 

 lustre and pale bronze-colored tarnish over most surfaces. 



No. 94. Marcasitic pyrite. Liskeard, Cornwall, England. 

 Thickly clustered groups of brilliant cubes of composite struc- 

 ture, forming crusts, pale yellowish white and splendent on 

 fracture ; upon gray copper and quartz. Decomposition : a beau- 

 tiful and lustrous orange-yellow tarnish. 



No. 95. Marcasitic pyrite. Waynesville, Ohio. Small 

 rounded nodules of irregular form : scattered through a crystal- 

 line fossiliferous schistose limestone. These are made up of 

 minute, glittering, rather dull, brownish yellow octahedra, or, in 

 a few nodules, of cubes with octahedral modifications ; on fresh 

 fracture, grayish white and splendent, with a slight yellowish 

 tinge, probably due to decomposition. Decomposition : irides- 

 cent yellow tarnish and dull reddish brown films of iron-oxide. 



No. 96. Marcasitic pyrite. Franklin, New Jersey. Sharp, 

 brilliant, brass-yellow, striated pyritohedra, yellowish white and 

 splendent on fracture, imbedded in white feldspar. In coarser 

 powder than that used for the determination in the table, 2.116 

 gms. of crystals yielded Sp. Gr. =4.642. Decomposition : 

 brilliant brass-yellow tarnish, a beautiful blue and red iri- 

 descence on some crystals. 



No. 97. Pyrite. Colorado. A cluster of dull, pale brass- 

 yellow, striated cubes, implanted and intergrown, Avith curved 

 faces by oscillation with the pyritohedron, grayish white and 

 splendent on perfectly fresh fracture ; sometimes with scattered 

 filmy yellowish spots, due to incipient decomposition ; mixed with 

 some blackish stony matter. Decomposition : rather dull brass- 

 yellow tarnish, partly iridescent on fracture-surfaces. 



No. 98. Marcasitic pyrite. Somerville, Massachusetts. 

 Very sharply defined, glittering yellowish cubes, sometimes dis- 

 torted or rectangular, rarely striated, occasionally with octahe- 

 dral planes upon their solid angles, yellowish white and brilliant 

 on fracture ; scattered through a gray argillaceous slate. De- 

 composition : a yellow tarnish common on fractured surfaces. 



