The transformation of limestone to dolomite (1), by the conversion of CaCO3 to CaMg(CO3)2. This occurs by the addition of magnesium to the sediment or rock and may take place soon after deposition or at various stages during diagenesis. Dolomitization is thought to occur in supratidal areas where sea water is drawn into the sediment and evaporation results in a high ratio of magnesium to calcium in the pore waters. Deeply buried limestone may become dolomitized if a mixture of fresh water and sea water passes through the rock. Dolomitization results in a 13% increase in porosity, making dolomites important reservoir rocks.