Tuning calcite magnesium content by soluble shell matrices: Insights into biomineral impurity control

In this study, the prismatic EDTA-soluble matrix (ESM) of Pinctada fucata was found to significantly reduce calcite Mg content when presented as an additive. Together with the Mg exclusion effect identified in the prismatic layer of P. fucata, a novel mechanism was proposed that organisms might use the additive effect to control the crystal impurity content in a solution of defined element composition. The precipitation inhibition assay and the direct ion-binding assay demonstrated that the ESM effect is realized neither by altering the precipitation rate nor by regulating the relative ion activity in the crystallizing solution. A plausible correlation between crystal impurity control and polymorphism determination was also discussed.