Substitution metasomatic

In actuality, the substitution mechanism is quite complex and diverse. Among forms of its manifestation is possible to identify two basic groups metasomatic substitution and hydrolytic leaching. 

Three media as a minimum participate in metasomatic processes two different minerals and ground water. If we assume activities of the participating minerals and H O dipole equal to 1, equilibrium and direction of the substitution reaction are defined by activities of components only in water composition. Equilibrium in the substitution process is reached when the activity product of acting components is equal to the value of the equilibrium constant of the general reaction, which is constant at given... 

In the absence of such equilibrium, one mineral is unavoidably substituted for the other. However, equilibrium among them and the direction of their mass transfer defines the ground water composition. For this reason metasomatic substitution depends not only on the nature of the minerals but also on the composition of ground water. As an example, let us review several of the most common substitution processes. 

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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