Iron sulfide

Iron sulfide is the chemical compound FeS, a black solid. It is made of iron and sulfide ions. FeS has iron in its +2 oxidation state. It reacts with acids such as hydrochloric acid to make hydrogen sulfide gas.

In plural, "iron sulfides" may refer to a range of chemical compounds composed of iron and sulfur. For example to FeS₂ (iron disulfide) found in the ground as the mineral pyrite. FeS₂ is shiny like a metal and has a bright golden color. That's why it is sometimes called "fool's gold".

Natural minerals

By increasing order of stability:

• Iron(II) sulfide, FeS, the less stable amorphous form;
• Greigite, a form of iron(II,III) sulfide (Fe₃S₄), analog to magnetite, Fe₃O₄;
• Pyrrhotite, Fe_1−xS (where x = 0 to 0.2), or Fe₇S₈;
• Troilite, FeS, the endmember of pyrrhotite;
• Mackinawite, Fe_1+xS (where x = 0 to 0.1);
• Marcasite, or iron(II) disulfide, FeS₂ (orthorhombic);
• Pyrite, or iron(II) disulfide, FeS₂ (cubic), the more stable endmember, known as fool's gold.