Many mineralization processes occur in convection-free conditions. Understanding these processes requires knowledge of crystal nucleation and growth processes in gels or high viscous sol systems. In this work, the crystallization parameters of calcium carbonate in an agarose viscous sol using counterdiffusion crystallization were monitored as a function of time. Additionally, by comparing the precipitation parameters in the high viscous sol entrapping charged polypeptides, namely, poly-L-lysine (pLys), poly-Laspartate (pAsp), and poly-L-glutamate (pGlu), it was possible to establish the polypeptide capability to inhibit, or eventually promote, the calcium carbonate nucleation and/or crystal growth processes. The polymorphism and morphology of the precipitates indicate that pLys only influences the growth mechanism of calcium carbonate without affecting the nucleation process. On the contrary, pAsp and, to a minor extent, pGlu affect both nucleation and growth. The application of this analysis can be extended to other additives and macromolecules able to affect crystallization processes.

Coral biomineralization is explored through calcium carbonate precipitation experiments, by counter-diffusion, using highly viscous agarose sol or gel entrapping soluble organic matrices extracted from Balanophyllia europaea and Leptopsammia pruvoti species, as well as diffusing Mg2+.

The molecular structure of the units that get incorporated into the nuclei of the crystalline phase and sustain their growth is a fundamental issue in the pathway from a supersaturated solution to the formation of crystals. Using a fluorescent dye we have recorded the variation of the pH value in time along a gel where CaCl2 and NaHCO3 counter-diffuse to crystallize CaCO3. The same pH–space–time distribution maps were also computationally obtained using a chemical speciation code (phreeqc). Using data arising from this model we investigated the space-time evolution of the activity of the single species (ions and ion pairs) involved in the crystallization process. Our combined results suggest that, whatever the pathway from solution to crystals, the neutral pair CaCO3° is a key species in the CaCO3 precipitation system.

The earliest evidence of life captured in lithified microbial mats (microbialites) predates the onset of oxygen production and yet, modern oxygenic mats are often studied as analogs based on their morphological similarity and their sedimentological and biogeochemical context. Despite their structural similarity to fossil microbialites, the presence of oxygen in most modern microbial mats disqualifies them as appropriate models for understanding early Earth conditions. Here we describe the geochemistry, element cycling and lithification potential of microbial mats that thrive under permanently anoxic conditions in arsenic laden, sulfidic waters feeding Laguna La Brava, a hypersaline lake in the Salar de Atacama of northern Chile. We propose that these anoxygenic, arsenosulfidic, phototrophic mats are a link to the Archean because of their distinctive metabolic adaptations to a reducing environment with extreme conditions of high UV, vast temperature fluctuations, and alkaline water inputs from combined meteoric and volcanic origin, reminiscent of early Earth.