192 Decomvosition of Iron Pyrites. 



pyritohedron, oscillation with the two producing a peculiar deep 

 striation and a roughening of the faces by somewhat rounded 

 projections ; grayish white and glistening on perfectly fresh 

 fracture ; in a greenish gray magnetitic schist. Decomposition : 

 blue iridescent tarnish on some crystals ; the fracture soon as- 

 sumes a yellowish tinge. 



No. 66 Limonite after pyrite. Texas, Lancaster County, 

 Pennsylvania. Sharply defined, striated cubes of reddish black 

 to reddish brown limonite, often with curved faces, flattened 

 and distorted, sometimes shining with high lustre. Some cubes 

 show hemihedral combinations with the pyritohedron and octa- 

 hedral modifications of the solid angles ; a few perfect octa- 

 hedra and modified pyritohedra also occur, rarely showing on 

 fracture minute remnants of unaltered pyrite, pale brass-yellow 

 and splendent ; on some crystals turgite forms a thin hard ex- 

 terior coat, with bright reddish streak and reddish brown pow- 

 der, surrounding and slightly adhering to the internal kernel of 

 limonite. 



No. 67. Pyrite. Joplin, Missouri. Brilliant, light yellow 

 cubes, with faces deeply striated and curved by oscillation with 

 the pyritohedron ; fracture, very pale brass-yellow, splendent 

 and conchoidal, and streak brownish black ; associated with 

 sphalerite, chalcopyrite, and dolomite. Also glittering, pale 

 brass-yellow pyritohedra with smooth faces, intimately mixed 

 with quartz ; fracture, very pale yellowish white, splendent and 

 uneven : scattered through a white schist. Decomposition : an 

 orange-yellow and blue tarnish. 



No. 68. Marcasitic pyrite. King Mountain Mine, G-aston 

 County, North Carolina. Bright yellowish cubes, with very 

 thinly foliated structure, well striated, with faces often a little 

 curved, and occasionally with angles modified by the octahedron 

 and faces further roughened thereby ; grayish white, very 

 slightly yellowish, and splendent on fracture ; imbedded in a 

 light gray argillaceous schist. Decomposition : sometimes iri- 

 descence, or a film of orange-colored iron-ochre. 



No. 69. Marcasitic pyrite. Schoharie, New York. Rusty 

 spherical nodules, consisting mainly of fibrous and radiating py- 

 rite, very pale yellowish white and sometimes grayish white, 

 with abundant yellow spots and films, on fracture, with an outer 



