And this is the offering you are to take from them: gold and silver and brass;
Referenced Verses
Deut 8:9 : 9 Where there will be bread for you in full measure and you will be in need of nothing; a land where the very stones are iron and from whose hills you may get copper.
Job 28:2 : 2 Iron is taken out of the earth, and stone is changed into brass by the fire.