It is just that if you look at metals such as gold and iron, the former is extremely rare and inert and cannot easily undergo chemical changes through combining with other materials, while the latter is used in huge quantities but is actually needed by the human body -- medics even recommend that we use iron cooking pots so as to provide us with supplementary iron.
只不過許多金屬如黃金與鐵，前者在地球上的量極少，又是惰性金屬，較不易與其他物質發生化學變化；鐵，雖然是人類使用量最大的金屬，由於人體所需鐵質含量頗高，還有醫生因此建議，人們可以多使用鐵鍋煮食，以補身體鐵的不足。