This work investigates the origin of the superior hardness of biogenic calcite by creating “model biominerals” from calcite single crystals containing glycine (0-7 mol%) or aspartic acid (0-4 mol%). Lattice distortions in these crystals were analyzed using x-ray diffraction and molecular dynamics simulations, while SS-NMR showed that the amino acids are incorporated as individual molecules. Nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. Finally, a dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules
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