Concentric zoning patterns in crystallizing (Cd,Ca)CO₃ solid solutions from aqueous solutions

Authors: Fernndez-Gonzlez ?; Prieto M.; Putnis A.; Lpez-Andrs S.

Source: Mineralogical Magazine, Volume 63, Number 3, 1 June 1999 , pp. 331-331(1)

Buy & download fulltext article:

Price: $14.18 plus tax (Refund Policy)

Abstract:

Otavite-calcite solid solutions have been synthesized to investigate the factors which control the patterns of compositional zoning. The equilibrium partitioning of otavite between the aqueous and the solid phase can be described by means of a function X_CdCO₃(X_Cd,aq)_eq, which relates the solid mole fraction and the aqueous activity fraction of Cd. According to this function, there is a strong preferential partitioning of Cd towards the solid. A set of experiments starting with parent solutions with different Cd²⁺/Ca²⁺ ratios was carried out. In these experiments nucleation takes place at high supersaturations and the Cd²⁺ and Ca²⁺ ions tend to be laid down in a ratio which deviates from the equilibrium distribution. Experimental nucleation data can be fitted to a curve X_CdCO₃(X_Cd,aq)_ef of the same functionality as that for equilibrium. After nucleation, supersaturation decreases as the crystals grow. During this process, substituting ions are not incorporated into the solid in the same stoichiometric proportion as in the aqueous solution. Therefore, crystal and fluid compositions tend to vary as growth proceeds and this evolution is registered as a compositional zoning. The curves X_CdCO₃(X_Cd,aq)_eq and X_CdCO₃(X_Cd,aq)_ef confine the reaction path corresponding to the growth process. Here, these curves are used to account for the observed zoning patterns.

Language: English

Document Type: Research article

Publication date: 1999-06-01

More about this publication?