Heterogeneous Nucleation and Growth of CaCO3 on Calcite (104) and Aragonite (110) Surfaces: Implications for the Formation of Abiogenic Carbonate Cements in the Ocean

Although near-surface seawater is supersaturated with CaCO3, only a minor part of it is abiogenic (e.g., carbonate cements). The possible reason for such a phenomenon has attracted much attention in the past decades. Substrate effects on the heterogeneous nucleation and growth of CaCO3 at various Mg2+/Ca2+ ratios may contribute to the understanding of the origin of abiogenic CaCO3 cements. Here, we used in situ atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy to study the heterogeneous nucleation and growth of CaCO3 on both calcite (104) and aragonite (110) surfaces. The results show that (1) calcite spiral growth occurs on calcite (104) surfaces by monomer-by-monomer addition; (2) the aggregative growth of aragonite appears on aragonite (110) surfaces through a substrate-controlled oriented attachment (OA) along the 001 direction, followed by the formation of elongated columnar aragonite; and (3) Mg2+ inhibits the crystallization of both calcite and aragonite without impacting on crystallization pathways. These findings disclose that calcite and aragonite substrates determine the crystallization pathways, while the Mg2+/Ca2+ ratios control the growth rate of CaCO3, indicating that both types of CaCO3 substrate in shallow sediments and aqueous Mg2+/Ca2+ ratios constrain the deposition of abiogenic CaCO3 cements in the ocean.