Uptake of fluoride by aragonite

The uptake of F by aragonite is attributed to the ion-exchange process, in which one CO₃^2? ion in the structure is replaced by two F^? ions. Under the equilibrium condition at 15° C and 1 atm., the partition of F between aragonite and aqueous solution is described by:

$\text{log}\text{(}\text{F}\text{]}\text{a}{}_{\mathrm{<mtext>F</mtext>}}\text{)=1.95 + 0.54}\text{log}\text{a}{}_{\mathrm{<mtext>Ca</mtext>}}$

were F] denotes the F content of aragonite in mol/g, and a_F and a_Ca are the aqueous activities of F^? and Ca²⁺, respectively. The equation was successfully applied to estimating the F content of marine aragonite.