High Quality Content by WIKIPEDIA articles! Magnesium silicide, Mg2Si, is an inorganic compound consisting of magnesium and silicon. As a powder magnesium silicide is dark blue or slightly purple in color. Silicon dioxide, SiO2, found in sand and glass, when heated with magnesium forms magnesium oxide, and, if an excess of magnesium is used, magnesium silicide is formed. The first product in this reaction is silicon, which then reacts further with magnesium to produce Mg2Si. The stoichiometry of these reactions are such that with a 2:1 Mg:SiO2 molar ratio, MgO is formed: