Orichalcum

Orichalcum (variously spelled orichalcon, orihalcon or orichalc): a metal first appearing in Plato's version of the Atlantis myth, where its main feature is being almost, but not quite, as valuable as gold. The name means "mountain copper" in Greek, and it, indeed, often appears the color of copper or bronze. Orichalcum's properties vary heavily from source to source: sometimes its schtick is strength, sometimes high value, sometimes magic resistance, sometimes room-temperature superconductivity. Sometimes it floats.