Tetra-auricupride is a very rare, natural alloy of gold and copper. The mineral's formula is AuCu and it crystallizes in the tetragonal system, thus the "tetra" prefix. There are lots of blebs and showings of gold, more likely electrum, by the colour of it. The Tetra-auricupride looks just like native copper and the areas of it are easy to see. Don't see this very often!