四氧化三铁是铁的氧化物，化学式为Fe₃O₄，有时被写成FeO·Fe₂O₃。

• 自然界中存在于磁铁矿中，含有各种杂质。

• 在氧气中燃烧铁粉：

• 铁与水蒸汽高温反应：

• 铁与二氧化氮加热反应：

• 氧化铁与氢气反应：

Iron(II,III) oxide is the chemical compound with formula Fe₃O₄. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe₂O₃) also known as hematite. It contains both Fe and Fe ions and is sometimes formulated as FeO ∙ Fe₂O₃. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is ferrimagnetic, but is sometimes incorrectly described as ferromagnetic. Its most extensive use is as a black pigment which is synthesised rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.