In nature, living organisms use peptides and proteins to precisely control the nucleation and growth of inorganic minerals and sequester CO2 via mineralization of CaCO3. Here we report the exploitation of a novel class of sequence-specific non-natural polymers called peptoids as tunable agents that dramatically control CaCO3 mineralization. We show that amphiphilic peptoids composed of hydrophobic and anionic monomers exhibit both a high degree of control over calcite growth morphology and an unprecedented 23-fold acceleration of growth at a peptoid concentration of only 50 nM, while acidic peptides of similar molecular weight exhibited enhancement factors of only similar to 2 or less. We further show that both the morphology and rate controls depend on peptoid sequence, side-chain chemistry, chain length, and concentration. These findings provide guidelines for developing sequence-specific non-natural polymers that mimic the functions of natural peptides or proteins in their ability to direct mineralization of CaCO3, with an eye toward their application to sequestration of CO2 through mineral trapping.