11.4 Alloys
People have been using metals for tools, weapons, currency, and decorations (particularly jewelry) for tens of thousands of years. For most of that time the available metals were only three group 11 element--Cu, Ag and Au. These were the only ones found as free metals in Earth's crust. Even so' most silver and copper occurs not as Ag and Cu but in ores such as argentite (Ag2S), chalcopyrite (CuFeS2), and chalcocite (Cu2s). Ores are naturally occurring compounds or mixtures of compounds from which elements can be extracted.