Assessing the feasibility of electrophoretic separation of CaCO₃ polymorphs for archaeological applications

We demonstrate a proof-of-principle method to separate particles of two CaCO₃ polymorphs, calcite and aragonite, based on surface charge density differences that affect electrophoretic mobility values. Calcite and aragonite standards show significant differences in their electrophoretic mobility distributions in polyphosphate-containing suspensions. Phosphate additives, which are commonly used to reduce particle aggregation, have a serendipitous added benefit of stabilizing CaCO₃ against dissolution. However, the mobility differences among archaeologically relevant samples, such as lime plasters and chalk, are not consistently different enough to make this a reliable separation strategy. Nevertheless, this study is important because it takes a new and fundamentally different approach to non-destructive separation of archaeological materials.