Dolomite is an anhydrous carbonate mineral composed of calcium magnesium carbonate, Used in horticulture, dolomite and dolomitic limestone are added to soils and soilless potting mixes as a pH buffer and as a magnesium source. Dolomite is also used as the substrate in marine (saltwater) aquariums to help buffer changes in pH of the water. Calcined dolomite is also used as a catalyst for destruction of tar in the gasification of biomass at high temperature. Water filtrations and Agriculture.