Experimental Studies in the System CaO-MgO-SiO_2-H_2O

The field evidence that many carbonatites are intrusive and possibly magmatic was incompatible with available experimental data until Wyllie and Tuttle (1960) demonstrated that liquids in the system CaO-CO_2-H2_O precipitate calcite at temperatures down to 640°C through a wide pressure range. The problem of the origin of carbonatites has since been examined by studying the phase relationships in systems containing the "synthetic carbonatite magma" and silicate minerals occurring in rocks associated with carbonatites. The increasing awareness in recent years of possible genetic connections between carbonatites and kimberlites (von Eckermann, 1948, 1958; Saether, 1957; Dawson, 1964; Garson, 1962; Davidson, 1964; Wyllie, 1967) led to the selection of forsterite as a suitable additional mineral component, giving the five-component system CaO-MgO- SiO_2-CO_2-H_2O. Sections through this system have been investigated by Franz (1965).