Abstract Proteins have found their way into many of Nature’s structures due to their structural stability, diversity in function and composition, and ability to be regulated as well as be regulators themselves. In this study, we investigate the constitutive amino acids that make up some of these proteins which are involved in CaCO₃ mineralization – either in nucleation, crystal growth, or inhibition processes. By assaying all 20 amino acids with vapor diffusion and in situ potentiometric titration, we have found specific amino acids having multiple effects on the early stages of CaCO₃ crystallization. These same amino acids have been independently implicated as constituents in liquid-like precursors that form mineralized tissues, processes believed to be key effects of biomineralization proteins in several biological model systems.