Project M: investigating the effect of additives on calcium carbonate crystallisation through a school citizen science program

Calcite and vaterite crystallisation is strongly influenced by the presence of additives during the reaction process, as demonstrated by organic molecules in biogenic calcium carbonate formation. The effect of additives on the lattice parameters of calcite and vaterite in syntheses are frequently reported, but only as discrete studies discussing a single polymorph. The intertwined nature of these polymorphs, due to their shared reaction pathway, is rarely discussed. In this work we report the results of a large scale citizen science project to explore the influence of amino acids and related additives on both polymorphs, highlighting their differences and commonalities in terms of the effect on the lattice parameters and polymorph selectivity. Crystallisation pathways of calcium carbonate are strongly influenced by the presence of additives. Through X-ray diffraction, samples made by the Project M Scientists reveal the effect of amino acid and related additives on the crystal structures of calcite and vaterite.