Magnesium oxide has the chemical formula MgO. It is a white or colorless, odorless compound. It is extracted from seawater or underground brine. It is also formed by the calcination of magnesium minerals such as magnesium carbonate and magnesium hydroxide. Magnesium oxide is present in the mineral periclase. Periclase is multihued, which makes it a substitute for gemstones. Periclase is also the substance responsible for providing streaks to white marble.

Medicinally, magnesium oxide is used as a short-term laxative for rapid elimination of the bowels, especially before surgery. It is also used as a dietary supplement when the amount of magnesium in the diet is not sufficient. Magnesium oxide use is not recommended for persons with heart and kidney problems. It is also not advisable for pregnant and lactating women. Magnesium oxide can interfere with other drugs like warfarin, aspirin, ranitidine, etc.

Apart from medicine, magnesium oxide also boasts several industrial uses. Magnesium oxide lined with carbon forms a tough refractory brick for metallurgical furnaces. Such magnesia bricks are resistant to corrosion and high temperature.

Magnesium oxide cement is also a good industrial binder. Magnesium oxide is high temperature resistant and so it is used to sheath thermocouples and also as filler in high temperature appliances such as rings of electric cookers.

Magnesium oxide is a highly versatile compound. Due to its refractive electro-optic properties, it is used as a protective layer in plasma screens. It is currently finding a use in semiconductor devices, though this property of magnesium oxide is yet to be fully explored.

Magnesium oxide is generally considered to be a harmless compound. There exist no special safety measures employed for people handling it. However, its fumes and dust may cause toxicity and allergies in certain individuals. Hence, workers in industries which involve grinding or crushing of magnesium oxide may be susceptible to airborne magnesium oxide related ailments.