A mineral having composition NiS and crystallising in the hexagonal system. Millerite usually occurs in hairlike tufts and radiating groups of slender to capillary crystals (see illus.). There is rhombohedral cleavage, but it is difficult to observe on the hairlike crystals. The hardness is 3–3.5 (Mohs scale) and the specific gravity is 5.5. The lustre is metallic and the colour pale brass yellow. Millerite forms at low temperatures, often in cavities and as an alteration of other nickel minerals. It is found in many localities in Europe, notably in Germany and the Czech Republic. In the United States it is found with pyrrhotite at the Gap Mine, Lancaster County, Pennsylvania; with hematite at Antwerp, New York; and in geodes in limestone at Keokuk, Iowa. In Canada large cleavable masses are mined as a nickel ore in Lamotte Township, Quebec.