Magnesium oxide, or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium. Formula: MgOMolar mass: 40.3044 g/molIUPAC ID: Magnesium oxideMelting point: 2,852 °CDensity: 3.58 g/cm³Boiling point: 3,600 °C Magnesia or magnesium oxide is an alkaline earth metal oxide.