60 NEW YORK STATE MUSEUM 



It resembles pyrite in crystallization and luster and is silver- 

 white to gray in color. 

 Like smaltite it is a source of cobalt compounds. 



Marcasite (white iron pyrites) FeS 2 



Marcasite is the orthorhombic iron disulfid, and has the same 

 composition as pyrite. 



The dimorphism ofi iron disulfid is all the more interesting 

 because pyrite represents an isomorphous group of sulfids and 

 arsenids which crystallize in similar forms of the isometric 

 system, and marcasite heads a similar isomorphous group 

 crystallizing in closely related forms of the orthorhombic 

 system. 



Twins and crystalline aggregates are common, resembling 

 spearheads, cockscombs, etc. often with radiated, stalactitic 

 structure as in pi. 16 2 . The color of marcasite is somewhat 

 whiter than that of pyrite, which it closely resembles. 



Marcasite occurs in Saxony, Bohemia and England, and in the 

 United States, associated with sphalerite, at the zinc mines of 

 Missouri, in Wisconsin and at Warwick, Orange co. N. Y. 



It is used in the manufacture of sulfuric acid. It is also 

 found in nodular concretions in the Tertiary and Cretaceous 

 clays of Long Island and Staten Island. 



Arsenopyrite (mispickel) FeAsS 



Arsenopyrite is the sulfarsenid of iron and contains 46$ 

 arsenic, 34.3$ iron and 19.7$ sulfur. 



Arsenopyrite crystallizes in the orthorhombic system in 

 forms resembling marcasite. A common 

 type of crystal is represented in fig. 173 

 and a characteristic grouping in pi. 17!. 

 Arsenopyrite commonly occurs in coarse 

 to fine granular masses or disseminated 

 grains. It is silver-white to gray, with a 

 metallic luster. 



Arsenopyrite is found principally in veins in crystalline rocks 

 associated with other metallic sulfids and arsenids. The 

 deposits of New South Wales, California and Alaska occasion- 

 ally carry some gold. It is found in many European localities, 



