The carbonatites are essentially carbonate-silicate rock with a great variety of other minerals. In this review the writer stresses the field and geochemical relationships of the carbonatites and alkalic igneous rocks and concludes that carbonatites were deposited by carbonatic solutions having a wide range of temperature, pressure, and concentration and derived from alkalic magmas during the process of silicate crystallization. Brogger's concept of carbonate magma is evaluated in the light of more recent field and laboratory investigations, and the conclusion is reached that a carbonate magma in the normal sense is less likely to exist than carbonate-rich solutions which at elevated temperature and pressure can have a higher concentration of dissolved ingredients than normally believed for hydrothermal solutions.
At many localities the carbonatites occur as veinlike or dikelike bodies or as cores in volcanic plugs of alkalic rocks. Recent investigations indicate that the carbonatites and related alkalic rocks represent a relatively unevaluated category of ore deposits that contain an impressive reserve of such rare commodities as niobium (columbium), titanium, zirconium, rare earths, barium, strontium, uranium, magnetite, phosphate, vermiculite, and agricultural lime.