Gold
Gold can be alloyed with various metals to give unique properties such as red gold (Cu), green gold (Cu and Ag) and white gold (Ni, Zn or Pt metal). The most common naturally occurring alloy is electrum, which is pale yellow and contains >20% Ag. The gold content (by weight) of an alloy is described in carats; pure gold (24 carat) is used in the Australian Nugget coins; 18 carat gold is 18/24 ...