Decomposition of Iron Pyrites. 199 



No. 99. Pyrite. Albertville, South Carolina. Bright yel- 

 lowish flattened cubes, finely striated, pale brass-yellow and 

 brilliant on fracture ; closely associated with quartz in adhering 

 encrusted films and imbedded particles, to which the low den- 

 sity, obtained for this pyrite, may be partly due. Deco7nposi- 

 tion : a slight dull tarnish. 



No. 100. Marcasitic pyrite. Koxbury, Massachusetts. Like 

 No. 46, with occasional better development of pyritohedral 

 faces ; associated with sphalerite and siderite. In another spec- 

 imen, the cubes are strongly striated and pass into distorted 

 forms, closely approaching the pyritohedron ; on some faces 

 there are implanted fine-grained mammillary crusts of glittering 

 drusy marcasite. Decompositioii : films of yellow to red tarnish 

 on the faces of the pyrite-crystals : a bronze-colored to brownish 

 black tarnish on the marcasite. 



No. 101. Pyrite. Monroe, Connecticut. Deeply striated, 

 distorted brilliant cubes of very pale brass-yellow color, with 

 modifications by the pyritohedron ; yellowish white, finely gran- 

 ular, and splendent on fractui-e, and sometimes enclosing grains 

 of white quartz. The specimen, as received, was mislabelled 

 '^ pyrrhotine." Under the microscope, the grains are seen to 

 enclose numerous particles of quartz and some reddish prisms 

 looking like topaz. Decomposition : a mere film of yellowish 

 tarnish common, iridescent under the loup. 



No. 102. Marcasitic pyrite. Pittston, Pennsylvania. Bright, 

 light brass-yellow, striated grains and scales, often with high 

 polish ; fresh fracture uneven, yellowish white, and splendent; 

 as thin coatings and scattered particles in a black carbonaceous 

 iron-stone, Octahedra with brilliantly polished faces and scaley 

 structure, and a few cubes, sometimes striated, with octahedral 

 modifications of their solid angles. Decomposition : a slightly 

 iridescent coppery tarnish on some plates. 



No. 103. Marcasitic pyrite. Jones' Mine, Pennsylvania. 

 Imperfect octahedra, with brilliantly polished faces, light brass- 

 yellow ; associated with magnetite, calcite, chalcopyrite, etc., 

 from the Coal. Decom,position : yellow tarnish common. 



No. 104. Marcasitic pyrite. Cumberland, England. Bril- 

 liant brass-yellow cubes, with slightly curved faces, and composite 

 and scaley in structure, pale yellowish white and splendent on 



