Here's a comparison of different forms of magnesium: Magnesium oxide is one of the most common forms of magnesium laxative and among the most studied. Like other forms of magnesium laxatives ...

and there is some evidence that 400–600 mg of magnesium oxide may help prevent migraines, especially in those who experience aura, or who have migraines related to their menstrual period.

Elemental magnesium is a fairly strong, silvery white, light-weight metal. It tarnishes slightly in air, and is thus protected against further oxidation by a thin impermeable layer of oxide.