Calcite Nucleation Research Articles

Controlled variation of calcite morphology using simple carboxylic acids

Water-soluble straight-chain monocarboxylic acids have been used to manipulate the processes of crystal nucleation and growth of calcium carbonate using the vapour diffusion method. The effect of solution pH was also investigated. Low initial solution pH (pH<2.5) led to >95% calcite nucleation, as compared with approximately 30% in control experiments with no added acid (pH∼5.3), irrespective of whether a mineral or organic acid was used to control the pH (note that the final solution pH was approximately 9 for reaction media that produced crystals). The presence of the mineral acid did not alter the expressed morphology of the calcite crystals, with the thermodynamically stable rhombohedral crystal habit dominating. In the presence of carboxylic acids, calcium carbonate crystal habit was considerably altered. The calcite habit expressed could be manipulated by varying the hydrophilic/hydrophobic balance within the carboxylic acid additive, by changing the hydrocarbon chain length, for a given calcium ion and additive concentration and partial pressure of carbon dioxide. The exact habit expressed could be further dictated by independently varying the partial pressure of carbon dioxide for a given concentration of calcium and carboxylic acid additive.

Modulating effect of acorn barnacle C-type lectins on the crystallization of calcium carbonate

The modulating effect of invertebrate C-type lectins on the crystallization of calcium carbonate was investigated. The multiple C-type lectins, named BRA-1, −2 and −3, isolated from the acorn barnacle Megabalanus rosa inhibited the nucleation and growth of calcium carbonate cyrstals. Among BRA, BRA-2 most efficiently inhibited the crystal nucleation of aragoite and calcite at the concentrations of >3.3 and >26 ⧎g/mL, respectively. The inhibitory activities of BRA were enhanced by the addition of various biomolecules such as D-glucosamine, D-galactosamine, chitosan oligosaccharides, L-arginine and L-aspartic acid. Although the crystals of aragonite and calcite were formed in the presence of lower concentrations of BRA, the shape and size of the crystals were changed. These results further indicate the participation of the lectins in biomineralization.

Photosynthesis, Respiration and Exopolymer Calcium-Binding in Biofilm Calcification (Westerhöfer and Deinschwanger Creek, Germany)

The impact of microbial activity on biofilm calcification in aquatic environments is still a matter of debate, especially in settings where ambient water has high CaCO3 mineral supersaturation. In this study, biofilms of two CO2-degassing karst-water creeks in Germany, which attain high calcite supersaturation during their course downstream, were investigated with regard to water chemistry of the biofilm microenvironment. The biofilms mainly consisted of filamentous cyanobacteria (Phormidium morphotype) and heterotrophic bacteria (including sulfate-reducing bacteria), which affect the microenvironment and produce acidic exopolymers. In situ and ex situ microelectrode measurements showed that a strong pH increase, coupled with Ca2 + consumption, occurred in light conditions at the biofilm surface, while the opposite occurred in the dark. Calcite supersaturation at the biofilm surface, calculated from ex situ Ca2 + and CO3 2− microelectrode measurements, showed that photosynthesis resulted in high omega values during illumination, while respiration slightly lowered supersaturation values in the dark, compared to values in the water column. Dissociation calculation demonstrated that the potential amount of Ca2 + binding by exopolymers would be insufficient to explain the Ca2 + loss observed, although Ca2 + complexation to exopolymers might be crucial for calcite nucleation. No spontaneous precipitation occurred on biofilm-free limestone substrates under the same condition, regardless of high supersaturation. These facts indicate that photosynthesis is a crucial mechanism to overcome the kinetic barrier for CaCO3 precipitation, even in highly supersaturated settings.

Molecular Evidence for Bacterial Mediation of Calcite Formation in Cold High-Altitude Caves

Three samples of moonmilk from high-altitude caves in northeast Italy were analysed for their lipid biomarker content, providing the first organic geochemical investigation into the relationship between cave bacterial communities and calcitic speleothems. The results demonstrate a positive association between the moonmilk deposits analysed and bacterial input, which we propose relates to bio-mediation of calcite nucleation processes. Comparison of the analysed moonmilk and a stalagmite from a geographically and climatically related cave suggest that this association is at least partially driven by the characteristics of the soil and overlying vegetation, thus demonstrating the potential use of moonmilk in palaeoenvironmental research.

A Novel Extrapallial Fluid Protein Controls the Morphology of Nacre Lamellae in the Pearl Oyster, Pinctada fucata

Mollusk shell nacre is known for its superior mechanical properties and precisely controlled biomineralization process. However, the question of how mollusks control the morphology of nacre lamellae remains unresolved. Here, a novel 38-kDa extrapallial fluid (EPF) protein, named amorphous calcium carbonate-binding protein (ACCBP), may partially answer this question. Although sequence analysis indicated ACCBP is a member of the acetylcholine-binding protein family, it is actively involved in the shell mineralization process. In vitro, ACCBP can inhibit the growth of calcite and induce the formation of amorphous calcium carbonate. When ACCBP functions were restrained in vivo, the nacre lamellae grew in a screw-dislocation pattern, and low crystallinity CaCO(3) precipitated from the EPF. Crystal binding experiments further revealed that ACCBP could recognize different CaCO(3) crystal phases and crystal faces. With this capacity, ACCBP could modify the morphology of nacre lamellae by inhibiting the growth of undesired aragonite crystal faces and meanwhile maintain the stability of CaCO(3)-supersaturated body fluid by ceasing the nucleation and growth of calcite. Furthermore, the crystal growth inhibition capacity of ACCBP was proved to be directly related to its acetylcholine-binding site. Our results suggest that a "safeguard mechanism" of undesired crystal growth is necessary for shell microstructure formation.

Heterogeneous nucleation and growth of calcium carbonate on calcite and quartz

The precipitation of calcium carbonate as a binding salt for the consolidation of loose sand formations is a promising approach. The heterogeneous nucleation and growth of calcite were investigated in supersaturated solutions. The ionic activities in the solutions tested were selected so that they included both supersaturations in which crystal growth took place only following the introduction of seed particles and supersaturations in which precipitation occurred spontaneously past the lapse of induction times. In the latter case the supersaturation conditions were sufficiently low to allow the measurement of induction times preceding the onset of precipitation. The stability domain of the calcium carbonate system was established at pH 8.50, 25 °C, measuring the induction times in the range between 30 min and 2 h. The rates of precipitation following the destabilization of the solutions were measured from the pH and/or concentration–time profiles. The induction times were inversely proportional and rates proportional to the solution supersaturation as expected. The high-order dependence of the rates of precipitation on the solution supersaturation suggested a polynuclear growth mechanism. Fitting of the induction time–supersaturation data according to this model yielded a value of 64 mJ/m 2 for the surface energy of the calcite nucleus. In the concentration domain corresponding to stable supersaturated solutions, seeded growth experiments at constant supersaturation showed a second-order dependence on the rates of crystal growth of calcite seed crystals. Inoculation of the stable supersaturated solutions with quartz seed crystals failed to induce nucleation. Raising supersaturation to reach the unstable domain showed interesting features: calcite seed crystals yielded crystal growth kinetics compatible with the polynuclear growth model, without any induction time. The presence of quartz seed crystals reduced the induction times and resulted in nucleation in the bulk solution. The kinetic data in the latter case were consistent with the polynuclear growth model and the surface energy for the newly forming embryo was calculated equal to 31.1 mJ/m 2, because of the dominantly heterogeneous nature of the process.

Calcite shape modulation through the lattice mismatch between the self-assembled monolayer template and the nucleated crystal face

The shapes of biologically formed calcite crystals are extremely versatile. Numerous studies have addressed the possible biological mechanism of crystal shape regulation. Synthetic assays have shown that the shape and morphology of calcite crystals can be modulated by inorganic or organic solution additives. Hardly any studies have to date discussed the concept of controlling the shape of these crystals by organic nucleating surfaces. We show in this paper that self-assembled monolayers (SAMs) that template calcite nucleation have two pronounced effects: in addition to inducing the highly oriented crystal growth (the phenomenon that we have extensively described in our previous studies), each SAM induces a clear modification of the calcite shape from its equilibrium rhombohedron. We demonstrate that this change in shape originates from the anisotropy of lattice mismatches that develop between the nucleating crystal face and the organic SAM in different directions. We present a model that gives qualitative predictions for the shape of crystals grown on a variety of SAM substrates, as a function of lattice mismatch, and show that these shapes correlate extremely well with the experimental results. We believe that this mechanism might be utilized by organisms in the biomineralization process.

Carbonate biomineralization induced by soil bacterium Bacillus megaterium

Biogenic carbonates spawned from microbial activities are common occurrences in soils. Here, we investigate the carbonate biomineralization mediated by the bacterium Bacillus megaterium, a dominant strain separated from a loess profile in China. Upon completing bacterial cultivation, the ensuring products are centrifuged, and the resultant supernatant and the concentrated bacterial sludge as well as the un-separated culture are added separately into a Ca-CO 3 containing solution for crystallization experiments. Results of XRD and SEM analysis indicate that calcite is the dominant mineral phase formed when the bacteria are present. When the supernatant alone is used, however, a significant portion of vaterite is also precipitated. Experimental results further reveal that the bacteria have a strong tendency to colonize the center area of the calcite {1 0 1 ¯ 4} faces. Observed crystal morphology suggests that the bacterial colony may promote the growth normal to each individual {1 0 1 ¯ 4} face of calcite when the cell concentration is high, but may retard it or even cause dissolution of the immediate substrate surfaces when the concentration is low. SEM images taken at earlier stages of the crystallization experiments demonstrate the nucleation of calcite on the bacterial cell walls but do not show obvious morphological changes on the nanometer- to submicron-sized nuclei. δ 13C measurements unveil that the crystals grown in the presence of bacteria are further enriched in the heavy carbon isotope, implying that the bacterial metabolism may not be the carbon sources for the mineralization. Based upon these findings, we propose a mechanism for the B. megaterium mediated calcite mineralization and conclude that the whole process involves epi- and inter-cellular growth in the local microenvironments whose conditions may be controlled by cell sequestration and proton pumping during bacterial respiration.

Calcium adsorption and changes of the surface microtopography of cyanobacteria studied by AFM, CFM, and TEM with respect to biogenic calcite nucleation

We investigated calcium interactions with the surface of individual living cells of the freshwater cyanobacterium Synechococcus leopoliensis PCC 7942 under illumination and calcite supersaturation, with respect to calcium carbonate nucleation on the cell surface. Immobilized living cells were scanned by Atomic Force Microscopy (AFM) with conventional and chemically modified tips which were coated with carboxylic groups, so‐called Chemical Force Microscopy (CFM). Calcium adsorption was heterogeneous and altered the surface charge of the cells. This was confirmed by bulk measurements of the zeta‐potential at different Ca2+ concentrations and compared to measurements made with other bivalent cations (Mg2+, Sr2+, Ba2+). Zeta‐potential increased rapidly (&lt;2 min) from −46.9 mV in calcium‐free solution to +0.8 mV in 22 mmol L−1 CaCl2 solution, using a 1.5 mmol L−1 NaHCO3 solution as background electrolyte in both cases. This was followed by the slow (several hours) formation of nonmineralized protuberances at the cell surface. These changes in the microtopography did not show obvious spatial relationship to surface charge or Ca2+ adsorption. The formation of the protuberances was reversible when Ca2+ was removed from the circumfluent solution. Ca2+ adsorption to the cell surface was faster than calcium‐induced changes in the surface microtopography and much faster than calcite nucleation on the cell surface which was observed on a fraction of the cells in previous bulk experiments under similar supersaturation.

Jurassic septarian concretions from NW Scotland record interdependent bacterial, physical and chemical processes of marine mudrock diagenesis

AbstractSeptarian concretions in the Staffin Shales Formation (Kimmeridgian, Isle of Skye) allow controls on concretion rheology and septarian cracking to be investigated. Stratabound concretions consist of anhedral ferroan calcite microspar enclosing clay and minor pyrite. Intergranular volumes range from 77% to 88%, and calcite δ13C and δ18O values in most concretion bodies range from −10·0‰ to −17·3‰ and +0·3‰ to −0·6‰ respectively, consistent with rapid and pervasive cementation in marine pore fluids. Septarian rupture occurred during incipient cementation, with a sediment volume reduction of up to 43%. Crack‐lining brown fibrous calcite records pore fluid re‐oxygenation during a depositional hiatus, followed by increasing Fe content and δ13C related to bacterial methanogenesis. Brown colouration results from an included gel‐like polar organic fraction that probably represents bacterially degraded biomass. A new hypothesis for concretion growth and septarian cracking argues that quasi‐rigid ‘proto‐concretions’ formed via binding of flocculated clays by bacterial extracellular polysaccharide substances (EPS). This provided rheological and chemical conditions for tensional failure, subcritical crack growth, volume contraction, calcite nucleation, and incorporation of degraded products into crack‐lining cements. Bacterial decay of EPS and syneresis of host muds provided internal stresses to initiate rupture at shallow burial. Development of septarian (shrinkage) cracks in muds is envisaged to require pervasive in situ bacterial colonization, and to depend on rates of carbonate precipitation versus EPS degradation and syneresis. Subsequent modification of septarian concretions included envelopment by siderite and calcite microspar, hydraulic fracturing associated with Cretaceous shallow burial or Palaeogene uplift; and cementation by strongly ferroan, yellow sparry calcite that records meteoric water invasion of the host mudrocks. An abundance of fatty acids in these spars indicates aqueous transport of organic breakdown products, and δ13C data suggest a predominantly methanogenic bicarbonate source. However, the wide δ18O range for petrographically identical cement (−1·3‰ to −15·6‰) is difficult to explain.

Sandstone-hosted concretions record evidence for syn-lithification seismicity, cavitation processes, and Palaeocene rapid burial of Lower Cretaceous deep-marine sandstones (Outer Moray Firth, UK North Sea)

Syn- and post-lithification cemented fractures are abundant in concretions formed during shallow burial of Hauterivian turbidites in the Outer Moray Firth. Early fractures are irregular, bifurcating, and contain entrained sand grains. They are confined to the concretion bodies, but commonly splay into narrower fracture swarms at the margins. Multiple, cross-cutting fills of calcite microspar have similar isotopic composition to adjacent concretionary cements, suggesting that rupture and cementation cycles occurred as host concretions lithified. Expulsion of cementing pore fluids from the fractures produced cement protrusions at concretion margins. A hydraulic fracture mechanism resulting from localized permeability heterogeneity and episodic seismic activity is proposed. Rapid seismic loading created high pore fluid pressures for fracture dilation in lithifying concretions and, through cavitation and CO 2 degassing, a trigger for rapid homogeneous nucleation of calcite. Many of the early structures were subsequently reactivated as brittle tensile fractures, and host a variety of mesogenetic cements. Reactivation probably occurred in response to stress amplification during rapid Palaeocene burial. By this time lithification of the concretions had dramatically changed their rheology and failure style. Minor permeability remained in the concretion cements adjacent to reactivated fractures, permitting invasion of intercrystalline voids by late diagenetic fluids.

Inhibition Mechanism of Magnesium Ion on Carbonation Reaction with Ca(OH)&lt;sub&gt;2&lt;/sub&gt; and CO&lt;sub&gt;2&lt;/sub&gt;

The objective of this study is to synthesize the single phase aragonite precipitated calcium carbonate by the carbonation process in the Ca(OH)2-MgCl2-CO2 system. Many researchers reported the influence of Mg2+ ion on the synthetic properties. The inhibition of calcite nucleation and crystal growth, distortion of calcite lattice, and change of surface electrification were investigated. Variety of particle size and aspect ratio were observed according to changes in the concentration of Ca(OH)2 slurry, temperature, and CO2 gas flow rate. The nucleation rate increased when decreasing the temperature and increasing the CO2 gas flow rate. Particle size and aspect ratio increased at high temperature, low CO2 gas flow rate, and high concentration of Ca(OH)2 slurry, however small-sized aragonite was obtained at low temperature.

Monohydrocalcite in the Arctic Ikka Fjord, SW Greenland: First Reported Marine Occurrence

Abstract Monohydrocalcite (MHC) has previously been known only from fresh-water and terrestrial environments. However, as documented in the present paper, MHC is a common mineral (up to 55%) in debris fragments from submarine ikaite (CaCO3·6H2O) tufa columns in the cold marine Ikka fjord, SW Greenland. The columns form where alkaline fresh water from submarine springs mixes with cold seawater and precipitates ikaite. Petrographical and geochemical data indicate that MHC represents a transitional diagenetic phase in the recrystallization process of metastable ikaite to final calcite. The stable-isotope data (δ13C and δ18O) document a closer relationship of MHC with the precursor ikaite than with calcite. Replacement of ikaite by MHC is suggested to take place by dissolution and precipitation in a semi-closed pore-water system dominated by alkaline spring water and with only limited access of seawater. In this environment, nucleation of calcite is inhibited by phosphate ions. Apart from calcite, aragonite and hydrous Mg carbonates were also observed in the tufa debris. The Mg carbonates represent late diagenetic phases, probably formed from recrystallization of MCH in normal seawater environments.

Aragonitic Algae in Calcite Seas: Effect of Seawater Mg/Ca Ratio on Algal Sediment Production

Abstract Secular variation in seawater Mg/Ca would have subjected the aragonite-producing codiacean algae to two intervals of low-Mg calcite seas (mMg/Ca mMg/Ca > 2) seas since their origin in the Ordovician. It is asserted that the aragonite + high-Mg calcite affinity of modern and Recent tropical seas (mMg/Ca > 2) has enabled the aragonitic Codiaceae to act as major carbonate sediment producers in these seas. To test this assertion, specimens of the sediment-producing codiacean alga Udotea flabellum were grown in artificial seawaters formulated at mMg/Ca ratios (1.0, 2.5, 5.2) that have occurred in the oceans throughout the geologic history of the Codiaceae. While the U. flabellum algae produced exclusively aragonite in both the artificial boundary seawater (mMg/Ca = 2.5) and the artificial aragonite + high-Mg calcite seawater (modern seawater; mMg/Ca = 5.2), the algae produced a portion (25 ± 3%) of their CaCO3 as low-Mg calcite (≤ 4 mol% MgCO3) in the artificial calcite seawater (mMg/Ca = 1.0), suggesting that their CaCO3 polymorph control can be partially overridden by ambient seawater chemistry. Primary productivity, calcification, and linear growth of the algae decreased with reductions in ambient Mg/Ca, despite increases in absolute Ca concentration of the seawater. Reduced calcification in the lower Mg/Ca seawaters is probably due to kinetic difficulties of producing aragonite from seawater that favors the nucleation of calcite. The decreased linear growth and primary production are likely associated with reductions in the ambient CO2 available for photosynthesis, resulting from the reduced calcification. These findings support the assertion that the dominant ecological and sedimentological roles of codiacean algae in Recent tropical seas is facilitated by a seawater Mg/Ca ratio that favors the nucleation of aragonite over calcite. Furthermore, producing aragonite in seawater that favors the nucleation of low-Mg calcite (mMg/Ca

Calcium Carbonate Crystallization in the Presence of Biopolymers

The influence on calcium carbonate crystallization of a series of biopolymers that contain carboxylic acid or sulfate functional groups was studied using pH and turbidity measurements, optical microscopy, and scanning electron microscopy. Without biopolymer, single calcite (104) rhombohedra were formed. In the presence of nongelling biopolymers (xanthan and gellan) in the conditions used, (104) rhombohedra formed aggregates that were “stack-like”, but in the presence of gelling biopolymers (pectin, κ-carrageenan, and sodium alginate) the aggregates were “rosette-like”. The “rosettes” were proposed to form by the nucleation of calcite on a gelled microparticle template to form a hollow shell. Low methoxy (LM) pectin was particularly effective at directing the growth of calcite rosettes and led to aggregates of radially aligned crystals. The influence of biopolymer concentration on calcite crystallization was studied for LM pectin and κ-carrageenan. In the former case, an increasingly favorable influence of...

Effect of Strontium Contaminants upon the Size and Solubility of Calcite Crystals Precipitated by the Bacterial Hydrolysis of Urea

The nucleation and growth of calcite precipitates induced by the bacterial hydrolysis of urea (ureolysis) from a Sr-contaminant inclusive, and a Sr-free artificial groundwater (AGW) mimicking the composition of the 90Sr contaminated Snake River Plain aquifer were investigated. Sr-free experiments exhibited a gradual increase in mean calcite crystal diameter (<1000 nm) from day (D) 1 to 6, while in the Sr-inclusive experiments, daily diameters were approximately constant from D1 to D6, and crystals were smaller (mean <840 nm). These data demonstrate a steady state had been attained early in the Sr-inclusive experiments from growth inhibition by Sr. Modeling of the crystal growth mechanisms on the USGS GALOPER software suggested crystal size distributions in the Sr-inclusive and Sr-free experiments were generated in the nucleation stage by a decreasing nucleation rate with surface-controlled growth, followed by supply-controlled and random growth. This occurred despite the availability of Ca2+ and HCO3-, implying crystal growth is limited bythe rate of solute advection to the crystal surface. Calculation of the solubility constant (In KsO(A)) demonstrates smaller crystals are more soluble, reflecting a higher molar surface area. The coprecipitation of Sr therefore generates smaller and thus more soluble crystals. However, this is unlikely to dramatically reduce the long-term effectiveness of Sr immobilization because when crystal growth had ceased in the Sr-inclusive AGW, > 99% of calcite precipitated and Sr coprecipitated occurred in large crystals with a low solubility.

Aragonite production in calcite seas: effect of seawater Mg/Ca ratio on the calcification and growth of the calcareous alga Penicillus capitatus

Abstract Previous studies have shown that secular variation in the Mg/Ca ratio of seawater throughout the Phanerozoic would have subjected the aragonite-producing codiacean algae to at least three transitions between the low-Mg calcite (molar Mg/Ca 2) nucleation fields in the oceans, since their origin in the Ordovician. These studies have asserted that major sediment production by codiacean algae in Recent tropical seas is permitted by the Mg/Ca ratio of modern seawater (molar Mg/Ca ∼5.2) remaining within the aragonitic/high-Mg calcite nucleation field (molar Mg/Ca >2). Here I present the results of experiments conducted to determine the effects of ambient Mg/Ca on the mineralogy, growth rate, primary productivity, calcification rate, and biomechanics of the codiacean alga Penicillus capitatus. P. capitatus specimens were grown in three artificial seawater treatments that mimic ancient seawater of differing Mg/Ca ratios, corresponding to the low-Mg calcit...

Thermodynamics of Epitaxial Calcite Nucleation on Self-Assembled Monolayers

Classical heterogeneous nucleation theory is used to describe the epitaxial nucleation of calcite on self-assembled monolayers (SAMs). Both spherical and faceted clusters are considered. The use of faceted clusters reveals a useful relation between the shape of very small crystals and the ratio of the heterogeneous and homogeneous nucleation barriers. The experimental approach of this paper concerns the measurement of the threshold driving forces for both homogeneous and heterogeneous nucleation of calcite. This is accomplished by preparing solutions with well-defined driving forces and by measuring the resulting types of nucleation that are observed after a fixed experimental time. The results of the experiments and the theoretical shape analysis are compared, and it is shown that in the experiments no homogeneous nucleation of calcite occurs for driving forces up to at least Deltamu/k(B)T approximately equal to 6.0. A calculation of the critical cluster size for heterogeneous nucleation results in a range of 2-28 growth units and faceted critical clusters from 3-28 growth units, depending on the value of the surface free energy of calcite. These sizes are 50-100 times smaller than the crystalline domain sizes of SAMs and therefore small enough to explain the promoting effect of the substrate.

Effect of Bicarbonate Ions on the Crystallization of Calcite on Self-Assembled Monolayers

We use molecular dynamics simulations to investigate the nucleation of calcite crystals on self-assembled monolayers. We show how the presence of bicarbonate ions adsorbed on the monolayer surface can both aid nucleation and control the orientation of the growth of the crystal. Using a simple model of the nucleation process and calculated interfacial energies, we calculate the enhancement (with respect to the homogeneous nucleation rate) of the nucleation of calcite on the (012) and (0001) faces. The calculations show clearly that the (012) face is favored over the (0001) face and that the nucleation rate is enhanced for self-assembled monolayers made from molecules containing an even number of carbon atoms in the alkyl chain over those containing an odd number.

Face‐Selective Nucleation of Calcite on Self‐Assembled Monolayers of Alkanethiols: Effect of the Parity of the Alkyl Chain

Aufgereiht: Eine Untersuchung selbstorganisierter Monoschichten von Sulfanylalkansäuren mit gerader und ungerader Kettenlänge auf Gold- und Silbersubstraten zeigt, dass die kristallographische Richtung darauf wachsender Calcitkristalle von der Orientierung der funktionellen Gruppen auf der Oberfläche abhängt (siehe Bild).