Empirical formula - Chemical formula that has been reduced by means of division. For example, (Si₃O₁₂) can be reduced to (SiO₄) by using the lowest common divisor, which is three. Three divided by three is one {so the second formula contains one silicon (Si) molecule}, and twelve divided by three is four {so the second formula contains four oxygen (O) molecules}. See The Chemical Properties of Minerals for more information.