iron sulfide can be formed by heating a mixture of powdered iron and sulfur & iron sulfide is made of iron and sulfur ->  iron sulfide is made of a mixture of iron and sulfur being heated  iron is a kind of element & sulfur is a kind of element ->  iron and sulfur are two elements  iron sulfide is made of a mixture of iron and sulfur being heated & iron and sulfur are two elements ->  iron sulfide is made of two elements  iron sulfide is made of two elements & a compound is made of two or more elements chemically combined -> iron sulfide is a compound