It seems copper is often found with admixtures of arsenic, nickel, mercury, antimony, bismuth, cadmium, zinc, gold, silver, ... I was wondering if some natural

It seems copper is often found with admixtures of arsenic, nickel, mercury, antimony, bismuth, cadmium, zinc, gold, silver, ... I was wondering if some naturally occurring copper ores could give a hardness advantage over pure copper, before the true copper-tin Bronze Age kicked off.