This is Mohawkite – and it can kill you.

Mohawkite is a very rare mineral discovered in 1899 at the Mohawk mines in Michigan’s Upper Peninsula, and is the only location on Earth where it can be found currently. It was first thought to be silver but proved to be an arsenide of copper and nickel. It’s composition is 63 to 69% copper, 3 to 7% nickel, 1 to 2% cobalt, and up to 28% arsenic.