Magnesian calcites cement composition

It is known that calcites formed 1n the presence of Mg + ions turn out to be magnesian calcites with 0.70 < x < 1 (1, 6 ). The calcites may be bulk precipitates as, for example, in marine cements or, in the case of seeded runs, may form coatings of a different composition from that of the bulk phase. Under special circumstances dolomite may result [ ). 

Metasomatic dolomitization is a common process, which actively affects the composition of both rocks and ground water. Three major types of dolomite are distinguished primary, precipitated together with the rock, secondary in the form of cement and the third one at dolomitization of limestones. In the latter case it forms due to the substitution of Mg instead of Ca. Because of this the very substitution process is considered as a number of sequential reactions of dissolution and precipitation. However, total substitution of dolomite instead of calcite is rare. Usually form limestones at various dolomitization stages (magnesian calcite, protodolomite). In its substance this is isomorphism of cations with the same valence, which may be presented by equation... 

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