It is the easy and widely used way to make light calcium carbonate and magnesium carbonate from dolomite by carbonizing process. During this process, the dolomite is calcined at different temperature, from 700°C to 950°C to get the mixture including either calcium carbonate and magnesia or calcia and magnesia. Then the mixture is blended with water in different temperature from room temperature to 80°C. As a result, it is supposed to get calcium hydroxide and magnesium hydroxide, but XRD analysis reveals that it is not accord with the theory. Magnesium hydroxide can not be obtained during this reaction. After the carbonization process, the calcium carbonate and a kind of mixture which is composed with different crystal phase of Mg5(CO3)4(OH)2[H2O]4 have been produced, instead of magnesium carbonate. The magnesia is gotten when the mixture is calcined at 450~750°C.