Hydromagnesite is a mineral with the chemical formula Mg5(CO3)4(OH)2·4H2O. This mineral is a hydrated carbonate mineral containing magnesium carbonate and hydroxide. Hydromagnesite typically forms as an oxidation product of magnesium deposits and can be found as a byproduct of magnesium mining.

In industrial applications, hydromagnesite is commonly used in the production of glass, ceramics, refractory materials, and chemical products. Additionally, in environmental applications, it can be utilized as a substitute for limestone to reduce water pollution caused by acid rain, as hydromagnesite has the ability to neutralize acids.

Also as a major application can be used as Flame retardent additive for Plastic (Polymer) compounds