196 Decomposition of Iron Pyrites. 



thick reddish broTvn crust of turgifce, with red streak, covering 

 the core of pyrite. 



No. 82. Pjrite. Schemnitz, Hungary. Somewhat flattened 

 cubo-octahedra, pale brass-yellow and splendent, forming a drusy 

 surface upon a very fine-grained, laminated, yellow layer of mar- 

 casitic pyrite, made up of alternately granular and fibrous lami- 

 nae, sometimes enclosing grains of radial structure ; with white 

 quartz and sphalerite. The specimen, as received, was mis-label- 

 led ''marcasite." The specific gravity determination was made 

 on fragments of the entire crust, including about one-fifth vol- 

 ume of crystals and also a very little adhering sphalerite. De- 

 composition : almost no tarnish on the crystals; in the layer be- 

 neath, films of white vitriol, mostly ferrous sulphate, occupy the 

 interstices between the fibres. 



No. 83. Pyrite. Colorado. Small cryptocrystalline grains, 

 pale brass-yellow and brilliant, made up of scaley aggregations 

 of minute octahedra and cubes with octahedral faces upon their 

 solid angles ; imbedded in radiating white barite. Decomposi- 

 tion: a slight brownish yelloAv tarnish on the exterior of the 

 grains. 



No. 84. Marcasitic pyrite. Nova Scotia. Small spherical 

 nodules in clay, made up of clustered aggregates of bright stri- 

 ated cubes, modified by minute planes of the octahedron and 

 pyritohedron, and also a few flattened pyritohedra: pale yellow- 

 ish white and brilliant on fracture. The surface has often been 

 rendered cellular, by the penetration of clay from the matrix. 

 Decomposition: minute traces of tarnish on a few faces ; the 

 powder becomes bronze-colored, on keeping a few months in a 

 dry atmosphere. 



No. 85. Marcasitic pyrite. Silver Valley Mine, Cabarrus 

 County, North Carolina. Brightly yellowish irregular grains, 

 sometimes showing the form of distorted cubes, modified by the 

 pyritohedron, grayish white, nearly silvery white, and splendent 

 on fresh fracture ; imbedded in white quartz, with galenite, 

 chalcopyrite and sphalerite. Decomposition: a dull yellow 

 tarnish common on many grains, with a few particles of yellow 

 iron-ochre in the interstices. 



No. 86. Marcasitic pyrite. Hazelton, Pennsylvania. Yel- 

 lowish cubes with rather dull lustre, scattered and in groups, 



