{TAIL ~ The iron sulfide} having a mackinawite structure which contains {HEAD ~ 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 0.7≦z≦1.4, as an essential component 
{ TAIL ~ The iron sulfide } having a mackinawite structure which contains { HEAD ~ 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 0.7≦z≦1.4 , as an essential component
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD 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