Biomineralization, the capability exhibited by many living organisms to produce hard tissues (e.g., bones, teeth, shells) involves extraordinarily complex and regular biochemical processes whereby the organo-mineral components are controlled and organized with specific crystalline forms and textures [1,2]. Considering only calcium carbonate polymorphs in molluscs, corals or sponges, a variety of hierarchical sub-millimetric structures and shapes are observed [3]. Consequently, biominerals often present outstanding material properties, like increased damage resistance [4] or bone regeneration induction [5], motivating strong efforts for developing biomimetic materials. Furthermore, the incorporations of trace elements (e.g., Mg, Sr, Cd, Ba) during the shell formation of CaCO 3 marine species directly register the environmental parameters. Thus, these shells are used in paleoclimatology as proxies for ocean paleo-temperature, productivity and circulation [6]. To circumvent the lack of a general model for the trace element incorporation, extensive empirical laws are derived, for each species and environmental conditions [see e.g., 6]. The variations of trace element concentration, observed within the shells [7], further strengthen the need for a deep understanding of the processes underlying the formation of the biominerals. Finally, as CaCO 3 is one of the most prominent minerals in the Earth's crust, it plays a major role in the global Carbon cycle [8]. Understanding the physico-chemical pathways underlying the synthesis of biomineral CaCO 3 in marine species would pave the way for refined models of climate evolution