Chemically, the distinction between limestone and dolostone is that the first one is chiefly composed of calcite, CaCO3, whereas the second is rich in MgCO3-Dolomite-. Therefo … re, the difference is limestone has Ca and Dolostone has Mg.   Mg is replacing Ca in the dolostone, in other words.   It is very difficult to make the distinction in a macro-scale samples. You will need optical or chemical procedures to differentiate each one.