The iron sulfide having a mackinawite structure which contains FeMxNySz wherein M represents an alkaline earth metal, N represents an alkali metal, and x, y and z, indicating the molar proportions of the respective elements, represent numbers satisfying 0.01<x≦0.5, y≦0.2 and {HEAD ~ 0.7≦z≦1.4}, as {TAIL ~ an essential component} 
as
The iron sulfide having a mackinawite structure which contains FeMxNySz wherein M represents an alkaline earth metal , N represents an alkali metal , and x , y and z , indicating the molar proportions of the respective elements , represent numbers satisfying 0.01 < x≦0.5 , y≦0.2 and { HEAD ~ 0.7≦z≦1.4 } , as { TAIL ~ an essential component }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL