Magnesium is everywhere it does not occur free in nature, but in combination with other elements it is the eighth-most abundant chemical element in the Earth’s crust and the third-most abundant element in seawater; it is even the ninth-most abundant in the Milky Way! In the human body, magnesium is the fourth most abundant ion and the eleventh most abundant element by mass, being stored in bones, muscles, and soft tissues.
https://talkutalku.com.ng/nurturing-the-brain-part-1-magnesium/