Millerite is a mineral composed of nickel sulfide, with the chemical formula Ni3S2. It typically forms in a yellow to golden color and has a fibrous or acicular crystal structure. This mineral is often found in hydrothermal veins and can be associated with other minerals such as chalcopyrite and pyrite. Millerite was first described in 1851 and is named after the American mineralogist William H. Miller. It is primarily used as a source of nickel, which is an important metal in various industrial applications, including the production of stainless steel and batteries.