Magnesian limestone is a type of sedimentary rock that is composed mainly of Magnesium and Calcium carbonates. Other names for this rock include dolostone, magnesium-rich limestone, and dolomitic limestone. Dolostone is a common synonym for magnesian limestone used in North America. In the UK, people often refer to Magnesian Limestone as the 'Great Limestone', the 'Middle Limestone', and the 'Lower Limestone.' Meanwhile, other synonyms for Magnesian limestone include dolomite rock, Magnesian marble, and dolomitized limestone. The use of these synonyms gives geologists and researchers different options when discussing this type of rock and its characteristics.