Decoupling local disorder and optical effects in infrared spectra: differentiating between calcites with different origins.

Perfect crystallinity is defi ned as three-dimensional, atomiclevel periodic order in a material. [ 1 ] The degree of crystallinity can be strongly affected by the specimen’s formation process and often plays an important role in its resulting chemical and mechanical properties. Calcium carbonate (CaCO 3 ), for example, exhibits a wide range of gradually changing crystallinity. The two extremes of this range are single-crystalline calcite, which exhibits a single periodic order across macroscopic distances, and amorphous calcium carbonate (ACC), [ 2 ] which exhibits a degree of short-range order but a lack of registry between adjacent local units that destroys all long-range periodic order. In biogenic, geogenic, and anthropogenic materials, variations in crystallinity and local atomic order have each provided valuable insights into material formation pathways. [ 3 ]