Iron
In the Name of God, the Compassionate, the Merciful: [57:25]
We have verily sent Our messengers with clear signs, and We revealed with them the Scripture and the Balance, so that mankind may uphold justice. And We sent down iron, wherein is great might, and [many] uses for mankind, and so that God may know those who help Him and His messengers through the Unseen. Assuredly God is Strong, Mighty.