Magnesium is relatively common. In addition, it represents about 2% of the Earth’s crust. Similarly, it can be found in the Earth’s mantle.
It can be found naturally occurring in minerals such as dolomite, magnesite, carnallite, serpentine & sea water (as magnesium chloride).
Globally, 1.1 million tonnes per year! (Magnesium Compounds Statistics and Information, 2020)