Breithauptite is a nickel antimonide mineral with the simple formula NiSb. Breithauptite is a metallic opaque copper-red mineral crystallizing in the hexagonal - dihexagonal dipyramidal crystal system. It is typically massive to reniform in habit, but is observed as tabular crystals. It has a Mohs hardness of 3.5 to 4 and a specific gravity of 8.23. It occurs in hydrothermal calcite veins associated with cobalt–nickel–silver ores. It was first described in 1840 from the Harz Mountains, Lower Saxony, Germany, and in 1845 for occurrences in the Cobalt and Thunder Bay districts of Ontario, Canada. It was named to honor Saxon mineralogist Johann Friedrich August Breithaupt (1791–1873).