Bricks made with Dead Burnt Magnesite or Magnesia (DBM) are an important category of basic refractories as it has the highest melting point i.e. 2800⁰C, among all basic refractories. Magnesite bricks are characterised by good resistance to basic slag as well as low vulnerability to attack by iron oxide and alkalies. They are widely used in applications such as glass tank checkers, as subhearth brick for electric arc furnaces and as back up lining in basic oxygen furnaces. Magnesite compositions are also widely used in ladle slide gate & gas purging refractories. Magnesite in combination with chrome, spinel and carbon is also used for various applications.

DBM of chinese origin is obtained from burning natural occuring magnesite (MgCO₃) at a temperature above 1400⁰C. At around 900⁰C, the CO₂ is released transforming magnesite to highly reactive caustic magnesia (MgO). At the temperature of 1400⁰C, magnesia starts crystallizing formic cubic crystal i.e. periclase, which reduces the reactivity of the magnesia. On further heating, the crystal combine, forming larger crystals, reducing drastically the reactivity of magnesia. With drastically reduced reactivity the magnesia is considered dead for practical purposes, hence termed as Dead Burnt.

The presence of silicate phases lower the melting point of magnesite. It is largely influenced by lime-to-silica ratio. When the lime-to-silica ratio is between 0 & 1, undesired low melting compound monticellite (CaO.MgO.SiO₂ MP 1500⁰C) coexist with forsterite (2MgO.SiO₂ MP 1850⁰C). In such a situation it is better to have no lime for refractory formulations.  At a lime-to-silica ratio of 1, undesired monticellite is the only silicate phase present in the composition. While at a lime-to-silica ratio of 1.5, the silicate phase would be merwinite (3CaO.MgO.2SiO₂ MP 1575⁰C), again low melting undesired compound for refractory formulations. As the lime-to-silica ration increases beyond 1.5, the temperature of initial liquid formation progressively increases. At a lime-to-silica ratio of 2, no merwinite remains and the highly refractory dicalcium silicate (2CaO.SiO₂ MP 1925⁰C) phase is formed. As the lime-to-silica ratio increases above 2, tricalcium silicate (3CaO.SiO₂ MP 1925⁰C) forms first, then free lime (CaO MP 2570⁰C). All the three phases exhibit high refractoriness.