Solubility product and supersaturation

A precipitation is a transformation that leads to a pure component S in a condensed phase (liquid or, more often, solid) starting from components belonging to the same solution (usually, condensed liquid or solid), which we will represent by the equation  

The Gibbs energy associated with this reaction is  

At equilibrium, this Gibbs energy is null and therefore  

The preceding constant, (T), is referred to as the solubility product of S in the initial solution. It depends on temperature. 

Remark- When the solvent, which is present in large amonnt, is one of the reactants of precipitation, its activity can be taken equal to 1 and thus omitted in the preceding product. 

---

Throughout this review of biomineralization, one outstanding phenomenon has been consistently evaded. This is the problem of apparent solubility products and supersaturation. It is obvious, however, that almost by definition this is the one phenomenon that directly relates to the whole problem, but it is consistently evaded because there is no simple theory to account for the observations. In order to highlight the importance of this phenomenon, therefore, an attempt will be made to relate extracellular theories to this concept. 

---