a light silver-white metallic element, malleable and ductile, quite permanent in dry air but tarnishing in moist air. it burns, forming (the oxide) magnesia, with the production of a blinding light (the so-called magnesium light) which is used in signaling, in pyrotechny, or in photography where a strong actinic illuminant is required. its compounds occur abundantly, as in dolomite, talc, meerschaum, etc. symbol mg. atomic weight, 24.4. specific gravity, 1.75.