Magnesium is a chemical element with symbol Mg and Atomic number 12. Its common oxidation number is +2. It is an Alkaline earth metal and the sixth-most-abundant element by both mass and moles in the Earth's crust(1). If H, He, Ne, and N are excluded, solar system abundance of magnesium is third, behind only oxygen and carbon and just slightly ahead of silicon(2). In the earth as a whole, it probably ranks fourth or fifth, behind iron, oxygen and silicon, and maybe calcium. Magnesium-rich silicate minerals make up a large fraction of the planet's mantle.
Magnesium is a very common element in the universe as a whole, because it is produced during what is called the "carbon burning" process which takes place in stars having over 8 solar masses at zero age (when hydrogen burning ignites)(3). While some of these stars become supernovae, some of the smaller ones end up as white dwarfs after blowing off an atmosphere rich in Mg.
REFERENCES:
- "Earth's Crust" table in "Abundances of the Elements (Data Page)"; Wikipedia. Note: source abundances are kg(X)/kg(tot)
- "Solar System Abundances" table in "Abundances of the Elements (Data Page)"; Wikipedia. Note: source abundances are mol(X)/mol(tot).
- "Carbon Burning Process"; Wikipedia.