Magnesium is a
chemical element with the
symbol Mg and
atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column (group 2, or
alkaline earth metals) of the
periodic table: all group 2 elements have the same
electron configuration in the outer electron shell and a similar crystal structure.
Magnesium is produced in large, aging
stars from the sequential addition of three
helium nuclei to a
carbon nucleus. When such stars explode as
supernovas, much of the magnesium is expelled into the
interstellar medium where it may recycle into new star systems. Magnesium is the eighth most abundant element in the
Earth's crust and the fourth most common element in the Earth (after
iron,
oxygen and
silicon), making up 13% of the planet's mass and a large fraction of the planet's
mantle. It is the third most abundant element dissolved in seawater, after
sodium and
chlorine.
