金 Jīn is 'gold':


It's supposed to be a picture of nuggets in the ground.

On the left and a little simplified (except in Traditional Characters), it indicates that the character is something to do with metal:

钱 Qián is 'money':

铁 Tiě is 'iron':


Common word: 地铁 dìtiě 'underground, subway, metro, MRT'