Iron + Oxygen

Iron + Oxygen ➜ Iron Oxide (Ferric Oxide)

4Fe + 3O₂ ➜ 2Fe₂O₃
Fe = 55.85
O = 15.99

Iron + Oxygen ➜ Iron Oxide (II,III) magnetite

3Fe + 2O₂ ➜ Fe₃O₄
Fe = 55.85
O = 15.99
167.7 g of Fe + 64 g of O₂ ➜ 231.7 g of Fe₃O₄


Note:
Iron II is ferrous (forms +2 ions)
Iron III is ferric (forms +3 ions)
Iron VIII is ferrate (rare)