{HEAD ~ The iron sulfide} having {TAIL ~ 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 0.7≦z≦1.4, as an essential component 
having
{ HEAD ~ The iron sulfide } having { TAIL ~ 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 0.7≦z≦1.4 , as an essential component
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL 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