Morphology Of Calcite Crystals Research Articles

Geothermometry of calcite spar at 10–50 °C

Carbonate geothermometry is a fundamental tool for quantitative assessment of the geothermal and geochemical evolution of diagenetic and hydrothermal systems, but it remains difficult to obtain accurate and precise formation temperatures of low-temperature calcite samples (below ~ 40 to 60 °C). Here, we apply three geothermometry methods (∆47-thermometry, nucleation-assisted fluid inclusion microthermometry—hereafter NA-FIM—and oxygen isotope thermometry) to slow-growing subaqueous calcite spar samples to cross-validate these methods down to 10 °C. Temperatures derived by NA-FIM and Δ47-thermometry agree within the 95% confidence interval, except for one sample. Regression analyses suggest that the real uncertainty of ∆47-thermometry exceeds the 1 SE analytical uncertainty and is around ± 6.6 °C for calcite spar that formed at 10–50 °C. The application of δ18O thermometry was limited to a few samples that contained sufficient primary fluid inclusions. It yielded broadly consistent results for two samples with two other geothermometers, and showed higher temperature for the third spar. We also found that calcite with steep rhombohedral morphologies is characteristic of low temperatures (11–13 °C), whereas blunt rhombohedra prevail in the 10–29 °C domain, and the scalenohedral habit dominates > 30 °C. This suggests that the calcite crystal morphology can be used to qualitatively distinguish between low- and higher-temperature calcite.

Self-repairing of shrinkage crack in mortar containing microencapsulated bacterial spores

The purpose of this research work was to evaluate the efficacy of microbially induced calcite precipitation (MICP) method in shrinkage crack repairing. Portland cement was combined with sand, bacterial spores, water, and nutrients to prepare self-healing composites. The microencapsulated bacterial spores were employed as an additive substance at ratios of 0%, 0.5%, and 1% by weight of cement. Specimens were kept in a climate-controlled room after casting to induce shrinkage crack. Crystalline phases formed in the specimen were identified using the X-ray diffraction (XRD) technique. The scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) method was used to investigate the morphology of precipitated calcite (CaCO3) crystals. Additionally, the specimen's permeability and compressive strength were also determined. When the bacterial spores were added to produce MICP procedure, the results demonstrated that it was successful in healing the shrinkage cracking. Within three days, the specimen with 1% spores could completely seal the shrinkage crack. According to the XRD patterns, the CaCO3 crystals appeared to promote the production of the calcite phase. Based on SEM/EDS investigation, the MICP process leads to concentrations of calcite crystal in certain regions, especially at the top surface of the crack. The 28-day compressive strength, on the other hand, decreased, owing to the addition of nutrients.

Entrapment of a Cytotoxic Drug into the Crystal Structure of Calcite for Targeted Drug Delivery.

Controlled drug release and targeted drug delivery can reduce systemic toxicity of chemotherapeutics by restricting drugs to the target organ and increasing the local concentration. As tumors and inflamed tissue are often surrounded by an acidic microenvironment, pH-responsive calcium carbonates (CaCO3) are promising vehicles for controlled drug delivery applications. The aim of this study was to evaluate the loading efficacy and release of a chemotherapeutic drug, Hydroxyurea (HU), into the crystal structure of calcite. Incorporation of HU did not alter the crystallinity, crystal size, or morphology of precipitated calcite crystals, as assessed by XRD and SEM. The amount of HU was quantified by High-Pressure Liquid Chromatography (HPLC) and showed that 6.7 ± 0.7 µg of HU could be for each milligram of calcite (0.016 mol% ± 0.002). In cell media, the optimal pH for controlled release was 5 (0.1 mg/mL released after 1 h). However, in vitro, pH below 6.5 was cytotoxic to human breast cancer cells (MCF-7). Direct contact studies, where particles were incubated with MCF-7 cells, showed that the amount of HU release from calcite was not high enough to kill the cell or arrest growth at pH 6.5. Pre-dissolved release studies, where the particles were pre-dissolved in acidic media to simulate complete drug release in vivo, pH neutralized, and exposed to the cells, showed that the amount of loaded HU reduced the survival/proliferation of MCF7. In conclusion, it is possible to integrate HU into the crystal structure of a calcite crystal and release the drug in vitro at concentrations that can slow the growth of cancer cells, without affecting calcite morphology and crystallinity. Further research is needed to investigate the in vivo behavior of the particles and whether the actual tumor pH is low enough to achieve complete drug release in vivo.

PU14, a Novel Matrix Protein, Participates in Pearl Oyster, Pinctada Fucata, Shell Formation

Biomineralization is a widespread biological process, involved in the formation of shells, teeth, and bones. Shell matrix proteins have been widely studied for their importance during shell formation. In 2015, our group identified 72 unique shell matrix proteins in Pinctada fucata, among which PU14 is a matrix protein detected in the soluble fraction that solely exists in the prismatic layer. However, the function of PU14 is still unclear. In this study, the full-length cDNA sequence of PU14 was obtained and functional analyses of PU14 protein during shell formation were performed. The deduced protein has a molecular mass of 77.8 kDa and an isoelectric point of 11.34. The primary protein structure contains Gln-rich and random repeat units, which are typical characteristics of matrix protein and indicate its potential function during shell formation. In vivo and in vitro experiments indicated PU14 has prismatic layer functions during shell formation. The tissue expression patterns showed that PU14 was mainly expressed in the mantle tissue, which is consistent with prismatic layer formation. Notching experiments suggested that PU14 responded to repair and regenerate the injured shell. After inhibiting gene expression by injecting PU14-specific double-stranded RNA, the inner surface of the prismatic layer changed significantly and became rougher. Further, in vitro experiments showed that recombinant protein rPU14 impacted calcite crystal morphology. Taken together, characterization and functional analyses of a novel matrix protein, PU14, provide new insights about basic matrix proteins and their functions during shell formation.

Acidic Monosaccharides become Incorporated into Calcite Single Crystals*.

Carbohydrates, along with proteins and peptides, are known to represent a major class of biomacromolecules involved in calcium carbonate biomineralization. However, in spite of multiple physical and biochemical characterizations, the explicit role of saccharide macromolecules (long chains of carbohydrate molecules) in mineral deposition is not yet understood. In this study, we investigated the influence of two common acidic monosaccharides (MSs), the two simplest forms of acidic carbohydrates, namely glucuronic and galacturonic acids, on the formation of calcite crystals in vitro. We show here that the size, morphology, and microstructure of calcite crystals are altered when they are grown in the presence of these MSs. More importantly, these MSs were found to become incorporated into the calcite crystalline lattice and induce anisotropic lattice distortions, a phenomenon widely studied for other biomolecules related to CaCO3 biomineralization, but never before reported in the case of single MSs. Changes in the calcite lattice induced by MSs incorporation were precisely determined by high-resolution synchrotron powder X-ray diffraction. We believe that the results of this research may deepen our understanding of the interaction of saccharide polymers with an inorganic host and shed light on the implications of carbohydrates for biomineralization processes.

Molecular Characterization of a Novel Shell Matrix Protein With PDZ Domain From Mytilus coruscus.

Mollusk shells are products of biomineralization and possess excellent mechanical properties, and shell matrix proteins (SMPs) have important functions in shell formation. A novel SMP with a PDZ domain (PDZ-domain-containing-protein-1, PDCP-1) was identified from the shell matrices of Mytilus coruscus. In this study, the gene expression, function, and location of PDCP-1 were analyzed. PDCP-1 was characterized as an ∼70 kDa protein with a PDZ (postsynaptic density/discs large/zonula occludes) domain and a ZM (ZASP-like motif) domain. The PDCP-1 gene has a high expression level and specific location in the foot, mantle and adductor muscle. Recombinantly expressed PDCP-1 (rPDCP-1) altered the morphology of calcite crystals, the polymorph of calcite crystals, binding with both calcite and aragonite crystals, and inhibition of the crystallization rate of calcite crystals. In addition, anti-rPDCP-1 antibody was prepared, and immunohistochemistry and immunofluorescence analyses revealed the specific location of PDCP-1 in the mantle, the adductor muscle, and the aragonite (nacre and myostracum) layer of the shell, suggesting multiple functions of PDCP-1 in biomineralization, muscle-shell attachment, and muscle attraction. Furthermore, pull-down analysis revealed 19 protein partners of PDCP-1 from the shell matrices, which accordingly provided a possible interaction network of PDCP-1 in the shell. These results expand the understanding of the functions of PDZ-domain-containing proteins (PDCPs) in biomineralization and the supramolecular chemistry that contributes to shell formation.

Significance of Fracture-Filling Rose-Like Calcite Crystal Clusters in the SE Pyrenees

Fracture-filling rose-like clusters of bladed calcite crystals are found in the northern sector of the Cadí thrust sheet (SE Pyrenees). This unusual calcite crystal morphology has been characterized by using optical and electron microscope, X-ray diffraction, Raman spectroscopy, δ18O, δ13C, 87Sr/86Sr, clumped isotopes, and major and rare earth elements + yttrium (REEs + Y) analysis. Petrographic observations and powder X-ray diffraction measurements indicate that these bladed crystals are mainly made of massive rhombic crystals with the conventional (104) faces, as well as of possibly younger, less abundant, and smaller laminar crystals displaying (108) and/or ( 1 ¯ 08) rhombic faces. Raman analysis of liquid fluid inclusions indicates the presence of aromatic hydrocarbons and occasionally alkanes. Clumped isotopes thermometry reflects that bladed calcite precipitated from meteoric fluids at ~60–65 °C. The 87Sr/86Sr ratios and major elements and REEs content of calcite indicate that these fluids interacted with Eocene marine carbonates. The presence of younger ‘nailhead’ calcite indicates later migration of shallow fresh groundwater. The results reveal that rose-like calcite clusters precipitated, at least in the studied area, due to a CO2 release by boiling of meteoric waters that mixed with benzene and aromatic hydrocarbons. This mixing decreased the boiling temperature at ~60–65 °C. The results also suggest that the high Sr content in calcite, and probably the presence of proteins within hydrocarbons trapped in fluid inclusions, controlled the precipitation of bladed crystals with (104) rhombohedral faces.

Benefits and drawbacks of applied direct currents for soil improvement via carbonate mineralization

The study presented herein adopts a new vision of the processes involved in carbonate mineralization induced by MICP from an electrochemical and crystal growth perspective. More precisely a specific line of focus refers to the species involved in the bio-chemical reactions and especially their net particle charge. By altering electro-chemical conditions via the application of direct electric currents, we observe distinctive trends related to: (i) overall reaction efficiency; (ii) carbonate mineralization/dissolution and (iii) spatial distribution of precipitates. The study introduces the concept of EA-MICP which stands for Electrically Assisted MICP as a means of improving the efficiency of soil bio-consolidation and overcoming various challenges which were previously reported in conventional MICP-based works. Results reveal both the detrimental and highly beneficial role that electric currents can hold in the complex, reactive and transport processes involved. An interesting finding is the “doped” morphology of calcite crystals, precipitated under electric fields, validated by microstructural observations.

Bacterial self-healing of concrete and durability assessment

Bacterial self-healing is an innovative technology allowing repairing open micro-cracks in concrete by CaCO3 precipitation. This bio-technology improves the durability of the structure. In this paper, peptone, yeast extract and Bacillus Subtilis were added as microbial adjuvant in concrete mix design. This led to a decrease in porosity resulting in an increase of strength, dynamic modulus as well as a reduction of water uptake, gas permeability and chloride permeation. Scanning electron microscopy, energy dispersive spectroscopy and raman spectroscopy showed that the microbial precipitations in the crack were CaCO3. Moreover, the morphology of calcite crystals was a needle-like, bouquet-like and rhombohedral-shaped. At 44 days, 400 μm crack surface width was completely filled. Hence, peptone, yeast extract and Bacillus Subtilis could be considered as a promising concrete admixture in enhancing durability and mechanical properties of concrete. Furthermore it is established that Eurocode 2 could be applied with confidence for predicting properties of bacterial concrete.

Model Anionic Block Copolymer Vesicles Provide Important Design Rules for Efficient Nanoparticle Occlusion within Calcite.

Nanoparticle occlusion within growing crystals is of considerable interest because (i) it can enhance our understanding of biomineralization and (ii) it offers a straightforward route for the preparation of novel nanocomposites. However, robust design rules for efficient occlusion remain elusive. Herein, we report the rational synthesis of a series of silica-loaded poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate)-poly(ethylene glycol dimethacrylate)-poly(methacrylic acid) tetrablock copolymer vesicles using polymerization-induced self-assembly. The overall vesicle dimensions remain essentially constant for this series; hence systematic variation of the mean degree of polymerization (DP) of the anionic poly(methacrylic acid) steric stabilizer chains provides an unprecedented opportunity to investigate the design rules for efficient nanoparticle occlusion within host inorganic crystals such as calcite. Indeed, the stabilizer DP plays a decisive role in dictating both the extent of occlusion and the calcite crystal morphology: sufficiently long stabilizer chains are required to achieve extents of vesicle occlusion of up to 41 vol %, but overly long stabilizer chains merely lead to significant changes in the crystal morphology, rather than promoting further occlusion. Furthermore, steric stabilizer chains comprising anionic carboxylate groups lead to superior occlusion performance compared to those composed of phosphate, sulfate, or sulfonate groups. Moreover, occluded vesicles are subjected to substantial deformation forces, as shown by the significant change in shape after their occlusion. It is also demonstrated that such vesicles can act as "Trojan horses", enabling the occlusion of non-functional silica nanoparticles within calcite. In summary, this study provides important new physical insights regarding the efficient incorporation of guest nanoparticles within host inorganic crystals.

Calcium Carbonate Crystal Shapes Mediated by Intramineral Proteins from Eggshells of Ratite Birds and Crocodiles. Implications to the Eggshell’s Formation of a Dinosaur of 70 Million Years Old

In this contribution we want to show how the intramineral proteins affect the crystal morphology of calcite crystals grown in vitro. Intramineral proteins from emu eggshells and two crocodile species were isolated, purified by ultrafast liquid chromatography, and characterized by biochemical and biophysical methods. We saw that the crystal habit of calcite was modified when intramineral proteins were present at certain concentration. Therefore, all crystal species were individually characterized by scanning electron microscopy (SEM) and by electron diffraction with an electron-reduced dosage in transmission electron microscopy. Additionally, transversal SEM micrographs of eggshells of four types of species, namely, emu, crocodile, hen, and dinosaur (70 million years old), were compared to track the changes produced by the interacting intramineral proteins. Finally, the organic sulfur content analysis of these eggshells was performed by using X-ray absorption techniques like X-ray fluorescence and X-ray absorption near-edge structure. From the analyses of the dinosaur eggshells, these X-ray absorption data showed a very characteristic organic sulfur bonding similar to that semiessential proteogenic amino acid l-cysteine, which implies that there is a possibility of having a very old intramineral protein similar to those found in emu and crocodiles.

Effect of Aspartic Acid and Glycine on Calcite Growth

Organic molecules control calcite growth and crystal morphology, influence biomineralization processes, and offer clues for optimizing antiscalants for industry. Here we quantified the effect of amino acid monomers, aspartic acid (Asp1), and glycine (Gly1), and their polymers (Aspn, Asp5, and Gly5), on calcite growth rate, in a constant composition setup. Asp1 and its polymers inhibit growth, with rate decreasing as amino acid chain length increases. For 2 mM Asp1, fractional inhibition (FI, where 1 represents complete inhibition) was 0.54; for 0.0012 mM Aspn, FI = 0.94. Gly1 and Gly5 only marginally affect growth (−0.1 < FI < 0.1); indeed, they slightly promote growth at most tested concentrations. Fitting of adsorption isotherms (Langmuir, Langmuir–Freundlich, Flory–Huggins) confirmed that Asp polymers adsorb strongly, explaining their strong control on calcite growth, but Gly1 and Asp1 adsorb less due to competition with carbonate ions. ΔGads (Aspn) = −39 kJ/mol; ΔGads (Asp5) = −50 kJ/mol; ΔGads (Asp1)...

Morphological changes of calcite single crystals induced by graphene–biomolecule adducts

Calcite has the capability to interact with a wide variety of molecules. This usually induces changes in shape and morphology of crystals. Here, this process was investigated using sheets of graphene–biomolecule adducts. They were prepared and made dispersible in water through the exfoliation of graphite by tip sonication in the presence tryptophan or N-acetyl-D-glucosamine. The crystallization of calcium carbonate in the presence of these additives was obtained by the vapor diffusion method and only calcite formed. The analysis of the microscopic observations showed that the graphene–biomolecule adducts affected shape and morphology of rhombohedral {10.4} faced calcite crystals, due to their stabilization of additional {hk.0} faces. The only presence of the biomolecule affected minimally shape and morphology of calcite crystals, highlighting the key role of the graphene sheets as 2D support for the adsorption of the biomolecules.

Secretory locations of SIPC in Amphibalanus amphitrite cyprids and a novel function of SIPC in biomineralization.

Settlement-inducing protein complex (SIPC) is a pheromone that triggers conspecific larval settlement in the barnacle Amphibalanus amphitrite. In the present study, immunostaining and scanning electron microscopy of SIPC revealed signals in the frontal horn pores and the secretions from carapace pores, suggesting that SIPC might be directly secreted from these organs in A. amphitrite cyprids. Further observations showed that the frontal horn pores could contact surfaces while cyprids were “walking”. Immunostaining for SIPC on the contacted surfaces displayed SIPC signals. These signals were similar to the frontal horn pores in size and morphology, suggesting that frontal horn pores might deposit SIPC. Besides, full-length SIPC was expressed and subsequent assays indicated that recombinant SIPC was able to bind to chitins and induce the precipitation of CaCO3. Furthermore, recombinant SIPC inhibited the formation of vaterites and regulated the morphology of calcite crystals. The crystals that formed with recombinant SIPC were more stable against water erosion. Overall, these results reported a novel function of recombinant SIPC that regulates crystal formation in barnacle shells.

Austromegabalanus psittacus barnacle shell structure and proteoglycan localization and functionality.

Comparative analyzes of biomineralization models have being crucial for the understanding of the functional properties of biominerals and the elucidation of the processes through which biomacromolecules control the synthesis and structural organization of inorganic mineral-based biomaterials. Among calcium carbonate-containing bioceramics, egg, mollusk and echinoderm shells, and crustacean carapaces, have being fairly well characterized. However, Thoraceca barnacles, although being crustacea, showing molting cycle, build a quite stable and heavily mineralized shell that completely surround the animal, which is for life firmly cemented to the substratum. This makes barnacles an interesting model for studying processes of biomineralization. Here we studied the main microstructural and ultrastructural features of Austromegabalanus psittacus barnacle shell, characterize the occurrence of specific proteoglycans (keratan-, dermatan- and chondroitin-6-sulfate proteoglycans) in different soluble and insoluble organic fractions extracted from the shell, and tested them for their ability to crystallize calcium carbonate in vitro. Our results indicate that, in the barnacle model, proteoglycans are good candidates for the modification of the calcite crystal morphology, although the cooperative effect of some additional proteins in the shell could not be excluded.

Physicochemical characteristics of drip waters: Influence on mineralogy and crystal morphology of recent cave carbonate precipitates

Speleothems are one of the most intensively explored continental archives for palaeoclimate variability. The parameters, however, that control speleothem petrography and its changes with time and space, specifically calcite crystal morphology and carbonate mineralogy, are still poorly understood. In order to shed light on processes and their products, precipitation experiments of recent carbonate crystals on watch glasses and glass plates were performed in seven selected caves. Drip water sites were analysed for their fluid Mg/Ca molar ratio, pH, degree of saturation for calcite and aragonite and drip rates. Corresponding precipitates were analysed with respect to their mineralogy, calcite crystal morphology and Mg/Ca molar ratio of calcite. The following results are found: High fluid Mg/Ca ratios are found only for caves situated in dolostone, thus the hostrock lithology indirectly controls the carbonate mineralogy and calcite crystal morphology of speleothems. The precipitation of aragonite in place of calcite occurred only in dolostone caves and is bound to very specific conditions. These are: high fluid Mg/Ca ratios (⩾0.5), high fluid pH (>8.2) and low fluid saturation indices for calcite (<0.8). These specific conditions are induced by slow drip rates of <0.2ml/min as often under more arid conditions, causing the precipitation of calcite/aragonite prior to reaching the stalagmite top. Due to this, fluid chemistry is altered, which in turn leads to changes in carbonate mineralogy and geochemistry on the stalagmite top. Calcite growth is inhibited at high fluid Mg/Ca ratios and hence, aragonite precipitation is kinetically stabilised. An increase of the drip water Mg/Ca ratio leads to an increased incorporation of Mg2+ into the calcite crystal lattice and thus, to a change in calcite crystal morphology. Four distinctive changes occur with increasing Mg2+ incorporation: (i) development of new forms (steeper rhombohedra and base pinacoid) at the edges and corners of the crystal seed, (ii) crystal habit tend to elongate along [001] due to slower growth of faces with high Mg2+ densities, (iii) reconstitution of crystal faces with low Mg2+ densities, and (iv) occurrence of calcite crystals with bended faces and edges due to very high Mg2+ (Mg/Ca ratios of 0.009–0.051) incorporation. Growth rates and possibly also organic compounds, however, may also affect the morphology of calcite crystals. Based on the data shown here, the relation of Mg2+ incorporation and the resulting changes in calcite crystal morphologies as well as the conditions of aragonite precipitation are now clearly better understood. Further work should aim at linking the calcite crystal morphology of watch glass precipitates with calcite crystal fabrics in speleothems in order to exploit the petrographic archive of speleothem deposits.

Obtainment of Spherical-Shaped Calcite Crystals Induced by Intramineral Proteins Isolated from Eggshells of Ostrich and Emu

In this work, we have performed a set of experiments to study how intramineral proteins affected the growth of calcite crystals and induced spherical growth. Intramineral proteins were first isolated from ostrich and emu eggshells and then purified by liquid chromatography. Samples of these proteins were analyzed by means of cyclic voltammetry to check their selectivity for carbonate ions. Then they underwent assays in solution through dynamic light scattering (DLS) to help us establish their homogeneity and stability (whether individually or in pairs) in the presence of carbonate ions. This was followed by in vitro crystallization experiments to determine how they affected the morphology of calcite crystals interacting with the intramineral proteins. Finally, scanning electron microscopy (SEM) showed that the morphology of the calcite crystals was strongly modified in the presence of these intramineral proteins.

In vitro calcite crystal morphology is modulated by otoconial proteins otolin-1 and otoconin-90.

Otoconia are formed embryonically and are instrumental in detecting linear acceleration and gravity. Degeneration and fragmentation of otoconia in elderly patients leads to imbalance resulting in higher frequency of falls that are positively correlated with the incidence of bone fractures and death. In this work we investigate the roles otoconial proteins Otolin-1 and Otoconin 90 (OC90) perform in the formation of otoconia. We demonstrate by rotary shadowing and atomic force microscopy (AFM) experiments that Otolin-1 forms homomeric protein complexes and self-assembled networks supporting the hypothesis that Otolin-1 serves as a scaffold protein of otoconia. Our calcium carbonate crystal growth data demonstrate that Otolin-1 and OC90 modulate in vitro calcite crystal morphology but neither protein is sufficient to produce the shape of otoconia. Coadministration of these proteins produces synergistic effects on crystal morphology that contribute to morphology resembling otoconia.

Influence of Near-Physiological Salines and Organic Matrix Proteins from Amorphous CaCO3 Deposits of Porcellio scaber on in Vitro CaCO3 Precipitation

Like most terrestrial isopods, Porcellio scaber stores cuticular calcium in sternal deposits before moulting. The deposits consist of spherules that are formed within a confined ecdysial space containing a fluid of known cationic composition. The spherules are composed of granular particles containing mainly amorphous calcium carbonate (ACC), little amorphous calcium phosphate, and an organic matrix. We precipitated calcium carbonate using near physiological, but phosphate-free salines and matrix proteins extracted from native deposits, and analyzed structure, mineral phase, and composition of the precipitates. Within the test solutions, the total soluble fraction leads to precipitation of ACC granules. Agglomerations of ACC granules and the dried soluble fraction of the organic matrix are virtually devoid of organic phosphates. The agglomerations mimic several aspects in the architecture of native sternal deposits and were stable for at least one month. The saline alone has no effect on the crystal phase but leads to changes in calcite crystal morphology due to the effects of magnesium. Bovine serum albumin (BSA) that was used as a control protein apparently has no effect on the mineral phase but in the presence of Mg2+ has severe effects on the surface structure of calcite crystals, suggesting a combined effect of BSA and Mg2+ on crystal growth.

The effect of alginates, fucans and phenolic substances from the brown seaweed Padina gymnospora in calcium carbonate mineralization in vitro

The mineralization of calcium carbonate (CaCO 3) in the brown seaweed Padina gymnospora is a biologically induced process and is restricted to the cell wall surface. It has been suggested that the CaCO 3 crystallization that occurs over the thallus cell wall surface is induced by changes in the surface pH caused by a local efflux of OH −, Ca ++ and HCO 3 − ions. However, no studies on the roles of the P. gymnospora cell wall components in this mineralization process had been performed. Therefore, we evaluated the influence of a subset of P. gymnospora cell wall molecules on CaCO 3 crystallization in vitro. The molecules tested were the anionic polysaccharides alginates and fucans (with potential nucleation activity) and phenolic substances (secondary metabolites with amphipathic property). The crystallization assays were performed using polystyrene microbridges as the crystallization apparatus. Crystals formed in the microbridges were analyzed using scanning electron microscopy. Interestingly, the results confirmed that the phenolic substances have the specific capability of changing the morphology of calcite crystals grown in vitro by inducing an elongated morphology in the direction of the c-axis. This morphology is similar to that induced by molecules that attach to { h k 0}-crystal planes. It was also shown that the alginates and the fucans do not specifically modulate the morphology of the growing crystals. In fact, these crystals exhibited a rounded shape due to the slower growth rates of several new crystal planes that appeared in the place of the original corners and edges.