'Iron' in the Bible

“I will go before youand level the uneven places;I will shatter the bronze doorsand cut the iron bars in two.

Because I know that you are stubborn,and your neck is ironand your forehead bronze,

I will bring gold instead of bronze;I will bring silver instead of iron,bronze instead of wood,and iron instead of stones.I will appoint peace as your guardand righteousness as your ruler.