Calcite Crystal Growth Research Articles

Influence of some polysaccharides on the production of calcium carbonate filler particles

The influence of different water-soluble polysaccharides, dextrans (cationic, anionic and non-ionic) and soluble starch, on the precipitation of calcium carbonate, has been investigated in the model system in which calcium hydroxide and carbonic acid were reactants. In the absence of additives, the formation of metastable phases, vaterite and amorphous calcium carbonate is observed at the early stage of the process, and as a consequence of the solution-mediated transformation process calcite appears in the system as the only solid phase in equilibrium. In the presence of starch, vaterite is found in the final precipitate, with the content increasing with the increase of starch concentration, probably as a consequence of calcite nucleation and crystal growth inhibition. Non-ionic dextran causes the inhibition of vaterite nucleation, which results in the formation of calcite as a predominant solid phase throughout the precipitation process. The crystal size of the so-formed calcite reduces by increasing the relative molecular mass ( M r) of neutral dextran. The presence of charged dextrans, either cationic or anionic, causes inhibition of the overall precipitation process: in the case of anionic dextran the inhibition seems to be the consequence of its reaction with Ca 2+ ions (supersaturation decrease), while cationic dextran most probably adsorbs electrostatically onto the negatively charged surfaces of calcite and vaterite.

Ultrastructural matrix–mineral relationships in avian eggshell, and effects of osteopontin on calcite growth in vitro

We investigated matrix-mineral relationships in the avian eggshell at the ultrastructural level using scanning and transmission electron microscopy combined with surface-etching techniques to selectively increase topography at the matrix-mineral interface. Moreover, we investigated the distribution of osteopontin (OPN) in the eggshell by colloidal-gold immunolabeling for OPN, and assessed the effects of this protein on calcite crystal growth in vitro. An extensive organic matrix network was observed within the calcitic structure of the eggshell that showed variable, region-specific organization including lamellar sheets of matrix, interconnected fine filamentous threads, thin film-like surface coatings of proteins, granules, vesicles, and isolated proteins residing preferentially on internal {104} crystallographic faces of fractured eggshell calcite. With the exception of the vesicles and granules, these matrix structures all were immunolabeled for OPN, as were occluded proteins on the {104} calcite faces. OPN inhibited calcite growth in vitro at the {104} crystallographic faces producing altered crystal morphology and circular growth step topography at the crystal surface resembling spherical voids in mineral continuity prominent in the palisades region of the eggshell. In conclusion, calcite-occluded and interfacial proteins such as OPN likely regulate eggshell growth by inhibiting calcite growth at specific crystallographic faces and compartmental boundaries to create a biomineralized architecture whose structure provides for the properties and functions of the eggshell.

Morphological and Kinetic Transformation of Calcite Crystal Growth by Prismatic-Associated Asprich Sequences

Many of the interesting mechanical and materials properties of the mollusk shell are thought to stem from the prismatic calcite crystal assemblies within this composite structure. It is now evident that proteins play a major role in the formation of these assemblies. Recently, a superfamily of seven conserved prismatic layer-specific mollusk shell proteins, Asprich, were sequenced, and the conserved 42 AA C-terminal sequence region of this protein superfamily was found to introduce surface voids or porosities on calcite crystals in vitro. Using AFM imaging techniques, we further investigate the effect that this 42 AA domain (Fragment-2) and its constituent subdomains, DEAD-17 and Acidic-2, have on the morphology and growth kinetics of calcite dislocation hillocks. We find that Fragment-2 adsorbs on terrace surfaces and pins acute steps, accelerates and then decelerates the growth of obtuse steps, forms clusters and voids on terrace surfaces, and transforms calcite hillock morphology from a rhombohedral fo...

Chemical Recognition of Carbonate Anions by Proteins Involved in Biomineralization Processes and Their Influence on Calcite Crystal Growth

In this work, we report the purification and characterization of struthiocalcins (SCA-1 and -2), two proteins isolated from the intramineral part of the ostrich’s eggshell. To obtain a better insight about their solubility behavior at different temperatures in water and in buffer solution, dynamic light scattering experiments were carried out. We studied the influence of the intramineral proteins SCA-1 and SCA-2 as well as the two other proteins present in eggs such as ovocleidin-17 (OC-17) and lysozyme (Lys) on the crystal growth behavior of calcium carbonate (calcite). This study showed important changes in the crystal habit and the nucleation process of calcium carbonate. Finally, the electrochemical methods were analytically used to confirm the interaction observed in the crystallization experiments. These results sorted out our dilemma about the selectivity and chemical recognition of proteins present in the eggshell for calcium or carbonate ions.

Colloidal-gold Immunocytochemical Localization of Osteopontin in Avian Eggshell Gland and Eggshell

During mineralization of the avian eggshell, there is a sequential and orderly deposition of both matrix and mineral phases. Therefore, the eggshell is an excellent model for studying matrix-mineral relationships and the regulation of mineralization. Osteopontin, as an inhibitor of crystal growth, potently influences the formation of calcium phosphate and calcium carbonate biominerals. The purpose of this study was to characterize matrix-mineral relationships, specifically for osteopontin, in the avian eggshell using high-resolution transmission (TEM) and scanning (SEM) electron microscopy to gain insight into how calcite crystal growth is structured and compartmentalized during eggshell mineralization. Osteopontin was localized at the ultrastructural level by colloidal-gold immunocytochemistry. In EDTA-decalcified eggshell, an extensive matrix network was observed by TEM and SEM throughout all regions and included interconnected fibrous sheets, irregularly shaped aggregates, vesicular structures, protein films, and isolated protein fibers. Osteopontin was associated with protein sheets in the highly mineralized palisades region; some of these features defined boundaries that compartmentalized different eggshell structural units. In fractured and undecalcified eggshell, osteopontin was immunolocalized on the {104} crystallographic faces of calcite-its natural cleavage plane. The specific occlusion of osteopontin into calcite during mineralization may influence eggshell structure to modify its fracture resistance.

Calcite crystal growth orientation: implications for trace metal uptake into coccoliths

AbstractInorganic calcite precipitation experiments were conducted to determine whether inducing specific orientations of calcite crystal growth can cause the enrichment of cations larger than Ca. Malonic acid (CH2(COOH)), a di-carboxylic acid, was used to poison growth on acute kink sites, promoting growth on obtuse kink sites, causing calcite crystals elongated along their c-axes to form in a mechanism similar to that seeninthe growth of E. huxleyi coccoliths. Calcite was precipitated with a range of malonic acid concentrations (0 to 10-1 M), and 9x10-5 M of either SrCl2 or MgCl2. The results show that calcite crystals precipitated in the presence of large malonic acid concentrations show significant elongation along the c axis, and suggest that increasing malonate concentrations corresponded with increasing DSr. Experiments with 10-1 M malonic acid caused elevated DSr comparable to that predicted for E. huxleyi coccolith calcite (Langer et al., 2006).

Earthworms produce granules of intricately zoned calcite

Research Article| December 01, 2008 Earthworms produce granules of intricately zoned calcite Martin R. Lee; Martin R. Lee 11Department of Geographical and Earth Sciences, Gregory Building, Lilybank Gardens, University of Glasgow, Glasgow G12 8QQ, UK Search for other works by this author on: GSW Google Scholar Mark E. Hodson; Mark E. Hodson * 22Department of Soil Science, University of Reading, Reading RG6 6DW, UK *E-mail: m.e.hodson@reading.ac.uk Search for other works by this author on: GSW Google Scholar Graham Langworthy Graham Langworthy 22Department of Soil Science, University of Reading, Reading RG6 6DW, UK Search for other works by this author on: GSW Google Scholar Geology (2008) 36 (12): 943–946. https://doi.org/10.1130/G25106A.1 Article history received: 28 May 2008 rev-recd: 07 Aug 2008 accepted: 18 Aug 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Martin R. Lee, Mark E. Hodson, Graham Langworthy; Earthworms produce granules of intricately zoned calcite. Geology 2008;; 36 (12): 943–946. doi: https://doi.org/10.1130/G25106A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Earthworms of the family Lumbricidae, which includes many common species, produce and secrete up to millimeter-sized calcite granules, and the intricate fine-scale zoning of their constituent crystals is unique for a biomineral. Granule calcite is produced by crystallization of amorphous calcium carbonate (ACC) that initially precipitates within the earthworm calciferous glands, then forms protogranules by accretion on quartz grain cores. Crystallization of ACC is mediated by migrating fluid films and is largely complete within 24 h of ACC production and before granules leave the earthworm. Variations in the density of defects formed as a byproduct of trace element incorporation during calcite crystal growth have generated zoning that can be resolved by cathodoluminescence imaging at ultraviolet to blue wavelengths and using the novel technique of scanning electron microscope charge contrast imaging. Mapping of calcite crystal orientations by electron backscatter diffraction reveals an approximate radial fabric to the granules that reflects crystal growth from internal nucleation sites toward their margins. The survival within granules of ACC inclusions for months after they enter soils indicates that they crystallize only within the earthworm and in the presence of fluids containing biochemical catalysts. The earthworm probably promotes crystallization of ACC in order to prevent remobilization of the calcium carbonate by dissolution. Calcite granules vividly illustrate the role of transient precursors in biomineralization, but the underlying question of why earthworms produce granules in volumes sufficient to have a measurable impact on soil carbon cycling remains to be answered. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Cyclic development of large, complex, calcite dendrite crystals in the Clinton travertine, Interior British Columbia, Canada

Bands of large (up to 4 cm long) three-dimensional crystallographic dendrites form the terrace fronts in an old travertine mound exposed near Clinton, British Columbia. The dendrites, with their long axes perpendicular to the terrace front, are characterized by numerous levels of branching. Each branch is formed of multitudes of skeletal rhombs, four- and six(?)-sided bipyramidal crystals, or prismatic hexagonal crystals that are precisely aligned along crystallographic precepts. Although individual branches are formed of one type of subcrystal, neighbouring branches may be formed of different subcrystal types. Highly supersaturated waters that were generated by rapid CO 2 degassing of the spring water during its turbulent flow over the steep terrace fronts probably drove dendrite precipitation. The presence of growth lines indicates that growth was episodic. Type I growth lines probably formed annually in response to seasonal climate changes whereas Type II growth lines, which formed less frequently, may reflect changes in the flow velocity and/or flow patterns of the spring waters. Early diagenetic modification of the dendrites involved crystal face enlargement, cements formed of trigonal prisms or needle-fiber crystals, microbial infestation that mediated substrate dissolution, and/or deposition of detrital calcite crystals that formed in the water column. Much of the diagenetic modification may have taken place during the periods when the dendrites had temporarily stopped growing. The dendrites in the Clinton travertine are an excellent example of complex, episodic calcite crystal growth that was extensively modified by early diagenetic processes in a surface environment. The same spring waters from which the dendrites were precipitated mediated much of the early diagenesis.

Hydrogels Coupled with Self-Assembled Monolayers: An in Vitro Matrix To Study Calcite Biomineralization

This paper describes the control of the nucleation and growth of calcite crystals by a matrix composed of an agarose hydrogel on top of a carboxylate-terminated self-assembled monolayer (SAM). The design of this matrix is based upon examples from biomineralization in which hydrogels are coupled with functionalized, organic surfaces to control, simultaneously, crystal morphology and orientation. In the synthetic system, calcite crystals nucleate from the (012) plane (the same plane that is observed in solution growth). The aspect ratio (length/width) of the crystals decreases from 2.1 +/- 0.22 in solution to 1.2 +/- 0.04 in a 3 w/v % agarose gel. One possible explanation for the change in morphology is the incorporation of gel fibers inside of the crystals during the growth process. Etching of the gel-grown crystals with deionized water reveals an interpenetrating network of gel fibers and crystalline material. This work begins to provide insight into why organisms use hydrogels to control the growth of crystals.

Chicken embryo utilization of egg micronutrients

IntroductionAvian embryos develop and grow from energy and nutrients storedin the egg by the hen. In this sense, breeder male contribution is notimportant. Follicular deposition of nutrients occurs over a wide range oftime, but becomes relevant during the week prior to ovulation. Amounts,but also forms, of nutrients deposited in the egg determine success ofembryo development and hatching of a healthy chick. To support theembryo during incubation, oxygen is the only nutrient not derived fromthe egg; however, adequate oxygen concentrations in the surroundingair and its free passage through well-established shell membraneporosities are essential. Developmental limitations and embryo mortalityare aggravated when any inadequacy in these conditions prevail.Macroscopically, the fertile egg has three components: shell, yolk,and albumen. Specific nutrients are mobilized by the embryo from eachof these parts. These typically have expected compositions, which arenotably affected by the hen’s nutrition.After oviposition, the egg may be submitted to changes due to inovo injection using the vaccination equipment routinely used inhatcheries. However, these injections are limited to small amounts, andpreferably done with more available forms of micronutrients. Researchon this matter is recent and usually directed to metabolic interventions,such as the role of substances which stimulate or mediate enzymetranscription.Egg ReservesMacroscopically, the egg is a simple structure with three majorcomponents (shell, albumen, and yolk), demonstrating uniquecharacteristics and playing specific roles during incubation. It is generallyagreed that each egg is built with a complete capacity to produce aperfect new organism. However, due to several reasons, this is notalways the case. In general, the composition of macromolecules in eggsis more constant than those elements usually found in a lower proportion,such as micronutrients. Since all egg constituents derive from the hen’sorganism, metabolic transformation of the hen’s feed is needed toobtain adequate embryo development and viable chicks at hatching.Egg shells consist of two main components: a matrix of protein fibersand col umns of calcium carbonate crystals in a proportion of 1:50 (Romanoff& Romanoff, 1949). A glycoprotein layer, the cuticle, covers the crystalsurface, and it is the last egg component to be deposited before oviposition.The cuticle has three main functions: prevention of excessive water loss(Peebles & Brake, 1986), protection from microbial infection (Roussel et al.,1988), and termination of calcite crystal growth (Dennis et al., 1996). Theshell matrix presents two regions: a mammillary region, connected to theouter shell membrane protein fibers, and a spongy one, associated to calcitecrystals deposited in layers on the mammillary matrix (Simkiss, 1968).

Scanning-Induced Growth on Single Crystal Calcite with an Atomic Force Microscope

We report observations of localized growth on the (1014) surface of single-crystal CaCO3 in supersaturated solutions while scanning with the tip of an atomic force microscope (AFM). At low contact forces, AFM scanning strongly enhances deposition along preexisting steps. This enhancement increases rapidly with increasing solution supersaturation, and is capable of filling in multilayer etch pits to produce defect-free surfaces at the resolution of the AFM. Attempts to achieve similar deposition rates in the absence of scanning require high supersaturations that produce three-dimensional crystal nuclei, which are important defects. Localized deposition produced by drawing the AFM tip back and forth across step edges can produce monolayer deposits extending well over a micron from the scanned area. These tip-induced deposits provide convincing evidence for the importance of ledge diffusion in calcite crystal growth.

Mass transfer of reactive crystallization in synthesizing calcite nanocrystal

An experimental study on the mass transfer and reactive crystallization of calcite nanocrystal was carried out in a Na 5 P 3 O 10 – Ca ( OH ) 2 – CO 2 – H 2 O multiphase system. According to the two-film theory and the two-steps crystal growth model, the kinetic characteristics in the system were investigated by the rate-comparison of the calcium hydroxyl dissolution, carbon dioxide absorption and calcium carbonate precipitation. The result indicated that the transfer resistance for the carbon dioxide absorption was negligible during the reactive crystallization, the rate-controlling step would shift from the crystallization of calcite to the dissolution of calcium hydroxyl at a turning time θ c . When reaction time was less than θ c , the calcite crystallization could be the rate-controlling step; while reaction time was larger than θ c , the calcium hydroxyl dissolution became the rate-controlling step. The analysis of the relationship of Damköhler number Da with surface integration effective factor η showed the crystallization kinetics would be affected by sodium tripolyphosphate. When [ Na 5 P 3 O 10 ] = 0 μ M , the calcite crystal growth could be controlled by the growth unit transport from liquid bulk to the crystal boundary. With an increasing sodium tripolyphosphate concentration, the rate-controlling step could be shifted from the bulk diffusion to the surface-reaction of growth units.

Inhibition Mechanism of Magnesium Ion on Carbonation Reaction with Ca(OH)<sub>2</sub> and CO<sub>2</sub>

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.

Influence of seawater chemistry on biomineralization throughout phanerozoic time: Paleontological and experimental evidence

Although some organisms exercise considerable control over their biomineralization, seawater chemistry has affected skeletal secretion by many taxa. Secular changes in the magnesium / calcium ratio and absolute concentration of calcium in seawater, driven by changes in rates of deep-sea igneous activity, have influenced the precipitation of nonskeletal carbonates: low-Mg calcite forms when the ambient Mg / Ca molar ratio is < 1, high-Mg calcite forms when the ratio is 1–2, and high-Mg calcite and aragonite form when the ratio is above 2. Reef builders and other simple organisms that are highly productive biomineralizers have tended to respond to changes in seawater chemistry in ways that mirror patterns for nonskelatal carbonates. Also, changes in the concentration of silicic acid in seawater have affected the ability of organisms to secrete siliceous skeletons. In laboratory experiments, organisms that secrete high-Mg calcite in the modern aragonite sea incorporate progressively less Mg in their skeletons with a reduction in the ambient Mg / Ca ratio, producing low-Mg calcite in “Cretaceous” seawater (Mg / Ca molar ratio = 1.0). Because algae that liberate CO 2 through calcification use it in their photosynthesis, an increase in the ambient Mg / Ca ratio results in accelerated aragonite secretion and overall growth for codiacean algae, and a decrease in the Mg / Ca ratio results in greatly accelerated growth rates for calcitic coccolithophores. Controlled experiments show that the increased concentration of Ca that accompanies a reduction of the ambient Mg / Ca ratio also accelerates coccolithophore population growth. Coccolithophores' production of vast chalk deposits in Late Cretaceous time can be attributed to the low Mg / Ca ratio and high Ca concentration in ambient seawater. The high Mg / Ca ratio and low Ca concentration in modern seawater apparently limit population growth for the large majority of modern coccolithophore species: ones that fail to respond to nitrate, phosphate or iron fertilization and are confined to oligotrophic waters. Presumably the low Mg / Ca ratio of ambient seawater was at least partly responsible for reduced reef-building by scleractinian corals in Late Cretaceous time. Some taxa have secreted more robust skeletons when seawater chemistry has favored their skeletal mineralogy. Strong intrinsic control of biomineralization can buffer a taxon against secular changes in seawater chemistry. Mollusks, for example, evolved the ability to severely limit the incorporation of Mg in their skeletal calcite in seawaters with Mg / Ca ratios as high as that of the present, but not in seawaters with still higher ratios. The ability to exclude Mg is useful because Mg reduces the rate of step growth of calcite crystals. On the other hand, labile skeletal mineralogy has permitted some taxa to respond to secular changes in the Mg / Ca ratio of seawater via phenotypic or evolutionary shifts of skeletal mineralogy. Sponges and bryozoans have apparently undergone evolutionary shifts of this kind polyphyletically. Increased incorporation of Mg in skeletal calcite with secular increases in the concentration of Mg in seawater has had little effect on seawater chemistry. In contrast, removal of Si by diatoms beginning in late Mesozoic time lowered the concentration of silicic acid in seawater, forcing siliceous sponges to secrete less robust skeletons.

The co-effect of collagen and magnesium ions on calcium carbonate biomineralization

The process of calcium carbonate biomineralization in the solution containing collagen and magnesium ions was studied in this paper. The results were characterized by using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect rules were obtained by the cooperation of collagen and magnesium ions in different concentration. The experiment results showed that in the presence of both collagen and magnesium ions, aragonite and vaterite were precipitated at low Mg/Ca ion concentration ratio, while only aragonite with regular spherical morphology was precipitated at high Mg/Ca ion concentration ratio. It indicated that collagen has a promotional effect on magnesium ions in controlling the polymorph of calcium carbonate crystal. A much wider range of calcium carbonate morphologies was observed in the presence of both collagen and magnesium ions. The experiments suggested that collagen acts in combination with magnesium ions to inhibit calcite crystal growth, while favoring the formation of aragonite crystals.

Inhibition of calcite crystal growth by polyphosphates

The inhibition of calcite crystal growth by pyrophosphate (P 2O 7 4−), tripolyphosphate (P 3O 10 5−), hexametaphosphate (P 6O 18 6−) and binary-polyphosphate blends in calcite-seeded solutions was investigated with various solution compositions using a pH-stat system. In a single polyphosphate system, tripolyphosphate was found to be the strongest inhibitor, followed by pyrophosphate and hexametaphosphate. The inhibition can be explained by the adsorption of polyphosphates on the calcite surface conforming to a simple Langmuir adsorption model. Through a detailed speciation analysis, CaP 2O 7 2− and CaP 3O 10 3− were found to be the primary species of pyrophosphate and tripolyphosphate responsible for adsorption of phosphate on the calcite surface, while the responsible species for hexametaphosphate could not be determined because of a lack of published stability constants. By comparing the equilibrium constants for the adsorption reaction, the inhibitory capabilities of polyphosphates are about two orders of magnitude greater than that of orthophosphate. In binary-polyphosphate systems, the inhibition of calcite crystal growth can be described by a competitive Langmuir adsorption model using the stability constants derived from single solute systems. The inhibitory behavior of commercially available phosphate blends that are marketed to prevent calcite scale formation were demonstrated to be similar to those of laboratory-prepared blends with the same chemical composition.

Acceleration of Calcite Kinetics by Abalone Nacre Proteins

Abalone shell nacre proteins act as surfactants to promote ion attachment at calcite steps, causing acceleration of the molecular-scale kinetics of calcite crystal growth. The proteins modify the shape of growing calcite (see Figure) through step-specific interactions, even though the proteins are larger than the atomic-scale steps. Understanding of crystal-growth control by interactions with proteins may give better control of new crystalline materials.

Caspartin and Calprismin, Two Proteins of the Shell Calcitic Prisms of the Mediterranean Fan Mussel Pinna nobilis

We used the combination of preparative electrophoresis and immunological detection to isolate two new proteins from the shell calcitic prisms of Pinna nobilis, the Mediterranean fan mussel. The amino acid composition of these proteins was determined. Both proteins are soluble, intracrystalline, and acidic. The 38-kDa protein is glycosylated; the 17-kDa one is not. Ala, Asx, Thr, and Pro represent the dominant residues of the 38-kDa protein, named calprismin. An N-terminal sequence was obtained from calprismin. This sequence, which comprises a pattern of 4 cysteine residues, is not related to any known protein. The second protein, named caspartin, exhibits an unusual amino acid composition, since Asx constitutes by far the main amino acid residue. Preliminary sequencing surprisingly suggests that the first 75 N-terminal residues are all Asp. Caspartin self-aggregates spontaneously into multimers. In vitro tests show that it inhibits the precipitation of calcium carbonate. Furthermore, it strongly interferes with the growth of calcite crystals. A polyclonal antiserum raised against caspartin was used to localize this protein in the shell by immunogold. The immunolocalization demonstrates that caspartin is distributed within the prisms and makes a continuous film at the interface between the prisms and the surrounding insoluble sheets. Our finding emphasizes the prominent role of aspartic acid-rich proteins for the building of calcitic prisms among molluscs.

Effects of trace element on crystal growth of calcite in aquatic system: Morphology analysis using electron back-scattering pattern technique

Effects of trace element on crystal growth of calcite in aquatic system: Morphology analysis using electron back-scattering pattern technique

Single crystal structure analysis of sea urchin spine calcites: Systematic investigations of the Ca/Mg distribution as a function of habitat of the sea urchin and the sample location in the spine

The hard skeleton of sea urchin spines consists of a monolithic single crystalline magnesian calcite with typical contents of MgCO 3 ranging from 2 to 12 mol% and about 0.1 weight% of occluded organic macromolecules. These macromolecules take effect on the calcite crystal growth, forming the spine shape in a porous spongy structure crossed by filled wedges of calcite radially arranged about the long axis of the spine. The single crystal structure analysis and polarization microscopy confirm the perfect alignment of the crystallites, thus the spine is a single crystal of calcite with the spine axis along the crystallographic c-axis, in agreement with earlier experiments. The magnesium content of the skeletal parts of the sea urchin is approximately linearly related with the water temperature of the sea urchin habitat. Elemental and chemical analysis showed an inhomogeneous Mg distribution in single spines: The Mg content increases from the spine-tip to the base by about 2 mol% at average. This structural inhomogeneity leads to a solid solution hardening of the material by the statistical incorporation of Mg 2+ ions in a crystal structure. The size difference between Ca 2+ and Mg 2+ ions impedes the propagation of cracks, thus affecting the fracture behavior of the biogenic calcite, which is conchoidal in contrast to the perfect {10.4} cleavage of geological calcite. The accumulation of Mg in the spine-base most likely serves to enhance this effect and thus strengthens the spine close to the shell.