Decomposition of Iron Pyrites. 189/ 



nish, sometimes with slight iridescence on many faces. 



No. 51. Pyrite. Smithfield, Rhode Island. Sharply defined 

 glittering, finely striated cubes, with mirror-like polish, and 

 octahedral modifications upon their solid angles, pale brass-yel- 

 low, and splendent on fracture ; imbedded in greenish white 

 slate. Decomjjosition : iridescent tarnish on some crystals. 



No. 52. Pyrite. Colorado. Striated pyritohedra, with an- 

 gles occasionally modified by the octahedron, pale brass-yellow 

 and splendent on fracture ; in groups implanted upon finely 

 granular pyrite and reddish black hematite. Decomposition : no 

 trace visible in the specimen. 



No. 53. Pyrite. Cornwall, Lebanon County, Pennsylvania. 

 Striated and roughened cubes, highly modified and distorted by 

 planes of the octahedron and pyritohedron, pale brass-yellow 

 and splendent on fracture, imbedded in a black argillaceous 

 schist. Decomposition : rather dull tarnish on most faces, with 

 orange to reddish brown films of iron-oxide. 



No. 54. Marcasitic })yrite. Guanajuato, Mexico. Mammil- 

 lary and drusy, hollow, highly iridescent crusts, grayish white 

 and splendent on fracture ; implanted on white quartz. The 

 minute crystals are cubes with composite scaley structure, the 

 smaller unmodified, the larger with octahedral planes upon their 

 solid angles ; also many cubo-octahedrons. Decomposition : a 

 beautiful iridescent and highly brilliant tarnish upon all sur- 

 faces, resembling that upon specimens of marcasite from Ga- 

 lena, 111. (Marcasite, Nos. 16, 20, 25, etc.) 



No. 55. Pyrite. Harford County, Maryland. A crust of 

 pyrite on greenish marmolite. The surface exhibits a clustered 

 aggregate of more or less distorted cubes, some even with rhom- 

 bic faces, their solid angles being occasionally modified by min- 

 ute faces of the octahedron ; pale brass-yellow and splendent on 

 fresh fracture. Decomposition : dull yellow tarnish, sometimes 

 with brownish stains. 



No. 56. Pyrite. Santa Gertrude Mine, California. Rather 

 dull yellow pyritohedra and cubes, pale brass-yellow and splen- 

 dent on fracture ; mixed with black stony matter. Decom- 

 position : dull brownish tarnish common, and sometimes a dull 

 blackish gray film ; the fresh fracture soon assumes a bronze- 

 colored tarnish. 



