Millerite is a mineral composed primarily of nickel sulfide, with the chemical formula NiS. It typically forms in a yellow to golden color and has a fibrous or acicular crystal structure, resembling fine needles. This mineral is often found in hydrothermal veins and can be associated with other minerals like pentlandite and chalcopyrite. Millerite is named after the American geologist William Miller, who studied the mineral in the 19th century. It is not commonly used in industrial applications but can be of interest to collectors and researchers studying nickel deposits and sulfide mineralogy.