When magnesium burns in air, it reacts primarily with oxygen to form magnesium oxide (MgO).

Here's the chemical equation:

2 Mg + O₂ → 2 MgO

This reaction produces a bright white light and a lot of heat.

While magnesium oxide is the primary product, a small amount of magnesium nitride (Mg₃N₂) can also form due to the reaction with nitrogen in the air.