Mohawkite is a rare rock consisting of mixtures of the elements arsenic, silver, nickel and copper, and the mineral skutterudite, with the chemical formula Cu3As up to Cu6As, and the most desirable material was usually found in white quartz matrix. Named after the Mohawk Mine in the Keweenaw Peninsula of the U.S. state of Michigan, where it was originally found, mohawkite has a hardness on the Mohs scale of 3.0 to 3.5 and a metallic luster. The rock's color ranges from brassy yellow to metallic gray, with some specimens having a blue or greenish surface tarnish. This nugget of mohawkite measures about 50 mm × 40 mm × 28 mm (2.0 in × 1.6 in × 1.1 in).Photograph credit: Heinrich Pniok