MINERAL OF THE MONTH: September 2008 Mohawkite

Technically “Mohawkite” is not a mineral but is a combination of copper arsenates with nickel and cobalt. It is also considered a variety of Domeykite. It is named after the original locality: the Mohawk Mine located in the Keeweenaw Peninsula of Michigan’s Upper Peninsula. This is the only location in the world that Mohawkite is found. The cubic crystals are rare in that the mineral more typically forms in masses, especially filling veins in hydrothermal vents. On a freshly fractured or mined surface, it appears whitish, but quickly tarnishes to brown. Sometimes the oxidized surface appears to have iridescence as it tarnishes. It has a hardness of between 3 and 3.5 with a specific gravity of between 7.2 and 7.9. It has a metallic luster with a brownish streak. Because of its speckled formation and combination of minerals, it has an uneven fracture. It is believed that the nickel arsenides crystallized first at higher temperatures. Later, fracturing occurred and some of the nickel was replaced by the copper arsenides-bearing solutions.

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