Magnesium has the atomic number 12 and is an alkaline earth metal with the symbol Mg. It is a common element, the eighth-most-abundant element in the Earth’s crust and ninth in the known universe as a whole. Magnesium is the fourth-most-common element in the Earth as a whole (behind iron, oxygen and silicon), making up 13% of the planet’s mass and a large fraction of the planet’s mantle.
The free element (metal) is not found naturally on Earth, as it is highly reactive (though once produced, it is coated in a thin layer of oxide (see passivation), which partly masks this reactivity). The free metal burns with a characteristic brilliant-white light, making it a useful ingredient in flares. You probably remember burning Magnesium Ribbon in school. Some of the light that burning magnesium produces is in the ultraviolet range. Just as ultraviolet light will burn your skin, it will also burn the retinas of your eyes if they are not protected, hence not looking directly at the light or using suitable safety eyewear.
Since magnesium is less dense than aluminium, these alloys are prized for their relative lightness and strength.
Magnesium has many uses, but most of us are familiar with aluminium-magnesium alloys, which are often found in cell phones and other electronic gadgets that must be strong yet light weight. Gardeners and tropical fish hobbyists are also very familiar with magnesium, since plants need it to grow (a magnesium deficiency is indicated by yellow leaves). Animals need small amounts of magnesium to support proper bodily functions too.
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