Magnesia can be divided into two categories: natural magnesia seawater magnesia synthetic magnesia. Mid-range magnesia natural magnesite is mainly derived natural magnesite, but due to the quality of raw ore, it is difficult to obtain high-purity high-quality products. So far, seawater magnesia has become the main source of magnesia used in industrialized countries. The theoretical content of MgO in magnesite is 47.3%, the remaining impurities include CaO, SiO2, iron, etc. Magnesite is heated to 700℃~800℃ in the air to decompose, which is called "light burned magnesium oxide", further heating Above 1530℃, it becomes inactive periclase becomes hard burned magnesia, which is called "dead burnt magnesia". The synthetic seawater magnesia used in industrial production is made seawater digested dolomite. The precipitated Mg(OH)2 is calcined to obtain MgO. The calcium to silicon ratio of the synthetic magnesia used for non-fired bricks is 0.3~0.5, the calcium to silicon ratio of high-purity seawater magnesia is above 1.7, its high temperature strength is high .