Quicklime Lime, sometimes referred to as quicklime, is a term commonly applied to a number of related materials. Pure lime is calcium oxide (CaO) formed by “burning” a form of calcium carbonate such as limestone or marble (CaCO3). Dolomite, a calcium magnesium carbonate (CaMg(CO3)2) can also be calcined to form dolomitic lime, which has different reactivity due to the presence of MgO. Lime can be mixed with water to form hydrated lime (Ca(OH)2), which some also refer to as lime. To further muddy the waters, in agriculture adding “lime” to the soil is not done with true lime but with limestone.