Iron

Iron is a resource.

Source
Iron is mined by placing a Metal Mine on tiles with Iron Deposits or by placing a Basalt Platform on a basalt lake tile.
 * Trace Deposit: +0.25/Iron a second
 * Low Deposit: +1.0/Iron a second
 * Medium Deposit: +1.5/Iron a second
 * High Deposit: +2.0/Iron a second
 * Very-High Deposit: +2.5/Iron a second. Only on Io

Uses
Iron has several uses:
 * Used by Steel Mills to produce Steel.
 * A building material for Steel Mills.