What is the difference between iron sulfide and a mixture of iron and sulfur?

I believe the question you are asking is "What is the difference between iron sulfide and a mixture of iron and sulfur?" Iron sulfide (FeS2) is a chemical compound comprised of iron and sulfur. Iron sulfide is chemically bonded through an exothermic reaction and the two elements no longer retain their separate, individual properties. The chemical compound is often a black color and is not attracted to a magnet. Iron sulfide is found naturally in the ground as the mineral pyrite.
A mixture of iron and sulfur, however, is just that: a mixture. It doesn't have to be comprised of a certain ratio of iron to sulfur, and the elements retain their unique properties. In a mixture of iron and sulfur, iron is still a silvery color and is attracted to a magnet, whereas sulfur maintains its yellow color and is not attracted to a magnet.