12mm x 19mm Copper - Silver "Half-breed" free form pendant in a Sterling Silver bezel setting. Pendant comes with a 18" silver chain as well.  

A rarer piece from the Keweenaw indeed. 

A physical mixture of native silver and native copper ). The insolubility of copper and silver produces specimens containing good crystallized examples of both minerals, often in epitaxy. Copper on silver is more rare than silver on copper.