Nickeline, or niccolite, is a nickel arsenide (NiAs) made up of approximately 44 % nickel and 56 % arsenic, with small, variable quantities of sulphur, iron and cobalt admixed. It is formed by hydrothermal modification of ultramafic rocks and associated ore deposits. Nickeline crystallizes in the hexagonal system. It usually occurs amorphous aggregates, with of a copper-red, metallic lustre. It has minor importance as an ore of nickel. This sample is from the Ernstschacht near Eisleben in Thuringen, Germany and it measures some 140 mm across.