Journal articles on the topic 'Aragonite'
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1
Farfan, Gabriela A., Amy Apprill, Anne Cohen, Thomas M. DeCarlo, Jeffrey E. Post, Rhian G. Waller, and Colleen M. Hansel. "Crystallographic and chemical signatures in coral skeletal aragonite." Coral Reefs 41, no. 1 (November 29, 2021): 19–34. http://dx.doi.org/10.1007/s00338-021-02198-4.
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AbstractCorals nucleate and grow aragonite crystals, organizing them into intricate skeletal structures that ultimately build the world’s coral reefs. Crystallography and chemistry have profound influence on the material properties of these skeletal building blocks, yet gaps remain in our knowledge about coral aragonite on the atomic scale. Across a broad diversity of shallow-water and deep-sea scleractinian corals from vastly different environments, coral aragonites are remarkably similar to one another, confirming that corals exert control on the carbonate chemistry of the calcifying space relative to the surrounding seawater. Nuances in coral aragonite structures relate most closely to trace element chemistry and aragonite saturation state, suggesting the primary controls on aragonite structure are ionic strength and trace element chemistry, with growth rate playing a secondary role. We also show how coral aragonites are crystallographically indistinguishable from synthetic abiogenic aragonite analogs precipitated from seawater under conditions mimicking coral calcifying fluid. In contrast, coral aragonites are distinct from geologically formed aragonites, a synthetic aragonite precipitated from a freshwater solution, and mollusk aragonites. Crystallographic signatures have future applications in understanding the material properties of coral aragonite and predicting the persistence of coral reefs in a rapidly changing ocean.
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Vinn, Olev. "The Role of Aragonite in Producing the Microstructural Diversity of Serpulid Skeletons." Minerals 11, no. 12 (December 18, 2021): 1435. http://dx.doi.org/10.3390/min11121435.
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Aragonite plays an important role in the biomineralization of serpulid polychaetes. Aragonitic structures are present in a wide range of serpulid species, but they mostly belong to one clade. Aragonitic structures are present in a wide range of marine environments, including the deep ocean. Aragonitic tube microstructures were studied using a scanning electron microscope. X-ray powder diffraction was used to identify the aragonite. Aragonite is used to build five different types of microstructures in serpulid tubes. The most common aragonitic irregularly oriented prismatic structure (AIOP) is also, evolutionarily, the most primitive. Some aragonitic microstructures, such as the spherulitic prismatic (SPHP) structure, have likely evolved from the AIOP structure. Aragonitic microstructures in serpulids are far less numerous than calcitic microstructures, and they lack the complexity of advanced calcitic microstructures. The reason why aragonitic microstructures have remained less evolvable than calcitic microstructures is currently unknown, considering their fit with the current aragonite sea conditions (Paleogene–recent).
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Rostovtseva, Yuliana. "Upper Miocene aragonite sediments of the Eastern Paratethys (Zheleznyi Rog section): Whiting events or not?" Annales g?ologiques de la Peninsule balkanique, no. 00 (2024): 6. http://dx.doi.org/10.2298/gabp240218006r.
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The upper Sarmatian and lower Maeotian unlithified aragonite sediments of the Zheleznyi Rog section (Taman Peninsula, Eastern Paratethys, Russia) were investigated by field observations and laboratory methods, including scanning electron microscopy, X-ray diffraction and isotope analyses. Aragonite sediments occur at separate intervals of the studied section, forming thin (millimeter-sized) interlayers with clays. These carbonate sediments consist almost entirely of crystals (individuals and twins) and aggregates of aragonite, ranging in size from 5 to 23 ?m. It is assumed that the isotopic composition (?13C = 5.7 and 5.3?, ?18O = -2.4 and -2.8 ? for upper Sarmatian and lower Maeotian aragonites, respectively) reflects the sedimentation conditions, chara cterized by reduced basin salinity, increased surface water bioproductivity, and periods of aridization. Abiotic precipitation of these aragonites most likely occurred due to the action of triggering mechanisms, which could include planktonic algae blooms (e.g. diatoms). The obtained results do not contradict the hypothesis that the studied aragonites may be considered as sediments of whiting phenomenon.
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Dean, Christopher D., Peter A. Allison, Gary J. Hampson, and Jon Hill. "Aragonite bias exhibits systematic spatial variation in the Late Cretaceous Western Interior Seaway, North America." Paleobiology 45, no. 4 (September 2019): 571–97. http://dx.doi.org/10.1017/pab.2019.33.
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AbstractPreferential dissolution of the biogenic carbonate polymorph aragonite promotes preservational bias in shelly marine faunas. While field studies have documented the impact of preferential aragonite dissolution on fossil molluscan diversity, its impact on regional and global biodiversity metrics is debated. Epicontinental seas are especially prone to conditions that both promote and inhibit preferential dissolution, which may result in spatially extensive zones with variable preservation. Here we present a multifaceted evaluation of aragonite dissolution within the Late Cretaceous Western Interior Seaway of North America. Occurrence data of mollusks from two time intervals (Cenomanian/Turonian boundary, early Campanian) are plotted on new high-resolution paleogeographies to assess aragonite preservation within the seaway. Fossil occurrences, diversity estimates, and sampling probabilities for calcitic and aragonitic fauna were compared in zones defined by depth and distance from the seaway margins. Apparent range sizes, which could be influenced by differential preservation potential of aragonite between separate localities, were also compared. Our results are consistent with exacerbated aragonite dissolution within specific depth zones for both time slices, with aragonitic bivalves additionally showing a statistically significant decrease in range size compared with calcitic fauna within carbonate-dominated Cenomanian–Turonian strata. However, we are unable to conclusively show that aragonite dissolution impacted diversity estimates. Therefore, while aragonite dissolution is likely to have affected the preservation of fauna in specific localities, time averaging and instantaneous preservation events preserve regional biodiversity. Our results suggest that the spatial expression of taphonomic biases should be an important consideration for paleontologists working on paleobiogeographic problems.
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Hoerl, Sebastian, Erika Griesshaber, Antonio G. Checa, and Wolfgang W. Schmahl. "The Biological Crystals in Chamid Bivalve Shells: Diversity in Morphology and Crystal Arrangement Pattern." Crystals 14, no. 7 (July 15, 2024): 649. http://dx.doi.org/10.3390/cryst14070649.
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Chamid bivalves are marine organisms that live in high-energy environments and are cemented to hard substrates. To avoid shell damage, the organisms form thick, densely ornamented shells. Shell material consists of aragonite, and the ornamentation may be either aragonitic or calcitic. The latter can be developed as scaly spines, rows of blades, or comarginal, radial arched lamellae. We investigated biological crystal morphology and mode of assembly of Chama arcana and Chama gryphoides shells. Structural characteristics were obtained from electron backscatter diffraction (EBSD) measurements, complemented with laser confocal and BSE imaging. We found a wide range of crystal morphologies and sizes, ranging from irregularly shaped calcite and/or aragonite prisms to tiny and thin aragonite laths. We observed four different modes of crystal assembly patterns: 1. strongly interlocked dendritic calcite units forming the ornamentation blades; 2. aragonite laths arranged to lamellae forming the outer shell layer, the layer adjacent to the calcite; 3. aragonite laths arranged into blocks comprising inner shell layers or aragonitic ornamentations; and 4. shell portions consisting of aragonite prisms, structured in size and crystal orientation, at muscle attachment sites. These four different types of crystal arrangements were observed for the shells of the investigated chamid species; however, they had slightly different strengths of structuring and slight variations in crystal organisation. Additionally, we observed unique microstructural features in Chama shells: We report ornamentation crystals resembling idiomorphic calcite and novel, twinned entities found at the changeover between the aragonitic layers. We highlight and discuss these differences and anomalies in this contribution.
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Nohl, Theresa, Jannick Wetterich, Nicholas Fobbe, and Axel Munnecke. "Lithological dependence of aragonite preservation in monospecific gastropod deposits of the Miocene Mainz Basin: Implications for the (dia-)genesis of limestone–marl alternations." Journal of Sedimentary Research 90, no. 11 (November 30, 2020): 1500–1509. http://dx.doi.org/10.2110/jsr.2020.057.
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ABSTRACTThe origin of limestone–marl alternations (LMA) and their diagenesis is still lively debated. The most disputed question is whether original variations in sediment input control the differentiation of the precursor sediment into limestone and marl, or if a LMA can form without compositional differences in the precursor sediment. The Miocene brackish-water deposits (Rüssingen Formation) from the Mainz–Weisenau quarry in central Germany offer the opportunity to tackle this question. They are developed as a monospecific alternation of planar beds of moderately and poorly lithified sands of aragonitic Hydrobia snails, corresponding to “limestones” and “marls” in LMA, respectively. XRD analyses and the monospecific composition reveal only minor to no changes in sedimentary input and allow comparison of the preservation of Hydrobia in both lithologies. The differential preservation of the aragonitic fossils in lithified and less lithified layers is documented in thin-sections. CaCO3 contents are high throughout the measured section. However, XRD analyses revealed high amounts of aragonite and low amounts of calcite in less lithified beds, and the opposite in lithified beds in which calcite is the main mineral phase. Mg-calcite is abundant in both lithologies. Although the less lithified beds have experienced significant loss of aragonite by dissolution, they still mainly contain aragonite since the precursor sediment contained only aragonitic shells and Mg-calcite crusts. The relative amount of aragonite is higher than in the more lithified beds because the lithified beds imported the dissolved aragonite, which precipitated as calcite cements. This shifted the aragonite–calcite ratio to higher values in the less lithified beds than in the more lithified beds, although it is counterintuitive at first sight. This is supported by thin-section analyses and point counting, revealing moderate to good preservation of Hydrobia or their replacement by calcite spar in lithified beds, but intense dissolution of aragonite in less lithified beds. The aragonite–calcite ratio and the differential preservation of Hydrobia fit the model of differential diagenesis in “classical” LMAs, which assumes early diagenetic aragonite dissolution in marls and reprecipitation as calcite cement in limestones. It is concluded that the studied succession—although an endmember of LMA—was differentiated into lithified and unlithified beds by incomplete differential diagenesis while minor primary differences are not reflected in the change in lithology. The results suggest that the differentiation of a homogeneous precursor sediment into a LMA is possible and caution should be exercised using lithological change or proxies which are potentially altered by CaCO3 redistribution for cyclostratigraphic analyses.
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Forjanes, Pablo, María Simonet Roda, Martina Greiner, Erika Griesshaber, Nelson A. Lagos, Sabino Veintemillas-Verdaguer, José Manuel Astilleros, Lurdes Fernández-Díaz, and Wolfgang W. Schmahl. "Experimental burial diagenesis of aragonitic biocarbonates: from organic matter loss to abiogenic calcite formation." Biogeosciences 19, no. 16 (August 22, 2022): 3791–823. http://dx.doi.org/10.5194/bg-19-3791-2022.
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Abstract. Carbonate biological hard tissues are valuable archives of environmental information. However, this information can be blurred or even completely lost as hard tissues undergo diagenetic alteration. This is more likely to occur in aragonitic skeletons because bioaragonite often transforms into calcite during diagenesis. For reliably using aragonitic skeletons as geochemical proxies, it is necessary to understand in depth the diagenetic alteration processes that they undergo. Several works have recently investigated the hydrothermal alteration of aragonitic hard tissues during short-term experiments at high temperatures (T > 160 ∘C). In this study, we conduct long-term (4 and 6 months) hydrothermal alteration experiments at 80 ∘C using burial-like fluids. We document and evaluate the changes undergone by the outer and inner layers of the shell of the bivalve Arctica islandica, the prismatic and nacreous layers of the hard tissue of the gastropod Haliotis ovina, and the skeleton of the coral Porites sp. combining a variety of analytical tools (X-ray diffraction, thermogravimetry analysis, laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction and atomic force microscopy). We demonstrate that this approach is the most adequate to trace subtle, diagenetic-alteration-related changes in aragonitic biocarbonate structural hard materials. Furthermore, we unveil that the diagenetic alteration of aragonitic biological hard tissues is a complex multi-step process where major changes occur even at the low temperature used in this study, well before any aragonite into calcite transformation takes place. Alteration starts with biopolymer decomposition and concomitant generation of secondary porosity. These processes are followed by abiogenic aragonite precipitation that partially or totally obliterates the secondary porosity. Only subsequently does the transformation of the aragonite into calcite occur. The kinetics of the alteration process is highly dependent on primary microstructural features of the aragonitic biomineral. While the skeleton of Porites sp. remains virtually unaltered for the entire duration of the conducted experiments, Haliotis ovina nacre undergoes extensive abiogenic aragonite precipitation. The outer and inner shell layers of Arctica islandica are significantly affected by aragonite transformation into calcite. This transformation is extensive for the prismatic shell layer of Haliotis ovina. Our results suggest that the majority of aragonitic fossil archives are overprinted, even those free of clear diagenetic alteration signs. This finding may have major implications for the use of these archives as geochemical proxies.
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Vinn, Olev. "Biomineralization in Polychaete Annelids: A Review." Minerals 11, no. 10 (October 19, 2021): 1151. http://dx.doi.org/10.3390/min11101151.
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Polychaete annelids are a very important group of calcifiers in the modern oceans. They can produce calcite, aragonite, and amorphous phosphates. Serpulids possess very diverse tube ultra-structures, several unique to them. Serpulid tubes are composed of aragonite or calcite or a mixture of both polymorphs. The serpulid tubes with complex oriented microstructures, such as lamello fibrillar, are exclusively calcitic, whereas tubes with prismatic structures can be composed either of calcite or aragonite. In serpulids, the calcareous opercula also have complex microstructures. Evolutionarily, calcitic serpulid taxa belong to one clade and the aragonitic taxa belong to another clade. Modern ocean acidification affects serpulid biomineralization. Serpulids are capable of biomineralization in extreme environments, such as the deepest part (hadal zone) of the ocean. The tubes of calcareous sabellids are aragonitic and have two layers, the inner irregular spherulitic prismatic layer and the outer spherulitic layer. The tube wall of cirratulids is composed of aragonitic lamellae with a spherulitic prismatic structure. In some other polychaetes, biominerals are formed in different parts of the animal body, such as chaetae or body shields, or occur within the body as granule-shaped or rod-shaped inclusions.
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He, Jianhan, and Ulrich Bismayer. "Polarized mapping Raman spectroscopy: identification of particle orientation in biominerals." Zeitschrift für Kristallographie - Crystalline Materials 234, no. 6 (May 27, 2019): 395–400. http://dx.doi.org/10.1515/zkri-2019-0004.
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Abstract The identification of the texture of biominerals and the particle orientation in the bivalve shells of Anodonta cygnea was performed using polarized Raman spectroscopy mapping measurements. A single crystal of aragonite served as a reference to disclose orientational information on the mesoscopic scale. The relative intensities of different Raman modes combined with the determination of depolarization ratio of the Ag Raman mode at 1087 cm−1 of an aragonite single crystal was used to indicate the angular variation of aragonite crystallites in biominerals. The imaging technique shows that the a- and b-axis of aragonite crystallites in both, nacreous and prismatic layers do not only have one orientation but they are organized in a domain-type arrangement. The angular divergence in the prismatic layer of the shells is larger and hence, the crystallites in the nacreous layer have a higher degree of co-orientation. Results provide relevant textural information about aragonitic shells and indicate a sensitive technique to evaluate the crystal orientation in biominerals.
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Katti, Kalpana S., Maoxu Qian, Daniel W. Frech, and Mehmet Sarikaya. "Low-loss Electron Energy-loss Spectroscopy and Dielectric Function of Biological and Geological Polymorphs of CaCO3." Microscopy and Microanalysis 5, no. 5 (September 1999): 358–64. http://dx.doi.org/10.1017/s1431927699000197.
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Previous work on microstructural characterization has shown variations in terms of defects and organization of nanostructures in the two polymorphs of calcium carbonate, calcite, and aragonite in mollusc shells. Large variations in mechanical properties are observed between these sections which have been attributed to variations in composite microstructure as well as intrinsic properties of the inorganic phases. Here we present local low-loss electron energy-loss spectroscopic (EELS) study of calcitic and aragonitic regions of abalone shell that were compared to geological (single-crystal) counterpart polymorphs to reveal intrinsic differences that could be related to organismal effects in biomineralization. In both sets of samples, local dielectric function is computed using Kramer-Kronig analysis. The electronic structures of biogenic and geological calcitic materials are not significantly different. On the other hand, electronic structure of biogenic aragonite is remarkably different from that of geological aragonite. This difference is attributed to the increased contribution from single electron excitations in biogenic aragonite as compared to that of geological aragonite. Implications of these changes are discussed in the context of macromolecular involvement in the making of the microstructures and properties in biogenic phases.
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DeCarlo, Thomas M., Michael Holcomb, and Malcolm T. McCulloch. "Reviews and syntheses: Revisiting the boron systematics of aragonite and their application to coral calcification." Biogeosciences 15, no. 9 (May 9, 2018): 2819–34. http://dx.doi.org/10.5194/bg-15-2819-2018.
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Abstract. The isotopic and elemental systematics of boron in aragonitic coral skeletons have recently been developed as a proxy for the carbonate chemistry of the coral extracellular calcifying fluid. With knowledge of the boron isotopic fractionation in seawater and the B∕Ca partition coefficient (KD) between aragonite and seawater, measurements of coral skeleton δ11B and B∕Ca can potentially constrain the full carbonate system. Two sets of abiogenic aragonite precipitation experiments designed to quantify KD have recently made possible the application of this proxy system. However, while different KD formulations have been proposed, there has not yet been a comprehensive analysis that considers both experimental datasets and explores the implications for interpreting coral skeletons. Here, we evaluate four potential KD formulations: three previously presented in the literature and one newly developed. We assess how well each formulation reconstructs the known fluid carbonate chemistry from the abiogenic experiments, and we evaluate the implications for deriving the carbonate chemistry of coral calcifying fluid. Three of the KD formulations performed similarly when applied to abiogenic aragonites precipitated from seawater and to coral skeletons. Critically, we find that some uncertainty remains in understanding the mechanism of boron elemental partitioning between aragonite and seawater, and addressing this question should be a target of additional abiogenic precipitation experiments. Despite this, boron systematics can already be applied to quantify the coral calcifying fluid carbonate system, although uncertainties associated with the proxy system should be carefully considered for each application. Finally, we present a user-friendly computer code that calculates coral calcifying fluid carbonate chemistry, including propagation of uncertainties, given inputs of boron systematics measured in coral skeleton.
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Toffolo, Michael B., Lior Regev, Eugenia Mintz, Kristin M. Poduska, Ruth Shahack-Gross, Christoph Berthold, Christopher E. Miller, and Elisabetta Boaretto. "Accurate Radiocarbon Dating of Archaeological Ash Using Pyrogenic Aragonite." Radiocarbon 59, no. 1 (February 2017): 231–49. http://dx.doi.org/10.1017/rdc.2017.7.
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AbstractObtaining accurate age determinations from minerals in archaeological ash is a major unsolved issue in radiocarbon (14C) dating. This is because the original 14C content of calcite, the main component of ash, is altered by isotopic exchange. Pyrogenic aragonite, another mineral phase recently discovered in ash, might preserve its 14C signature through time. Using a new method based on density separation and step combustion, we were able to isolate and date aragonitic ash from an archaeological destruction horizon of known age. Here we show that the 14C age of aragonite matches the age of the destruction horizon. Our results demonstrate that pyrogenic aragonite is a short-lived material suitable for 14C dating and directly related to human activities involving the use of fire, thus bearing major implications for the establishment of absolute chronologies for the past 50,000 yr.
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Foote, Michael, James S. Crampton, Alan G. Beu, and Campbell S. Nelson. "Aragonite bias, and lack of bias, in the fossil record: lithological, environmental, and ecological controls." Paleobiology 41, no. 2 (February 24, 2015): 245–65. http://dx.doi.org/10.1017/pab.2014.16.
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AbstractMacroevolutionary and macroecological studies must account for biases in the fossil record, especially when questions concern the relative abundance and diversity of taxa that differ in preservation and sampling potential. Using Cenozoic marine mollusks from a temperate setting (New Zealand), we find that much of the long-term temporal variation in gastropod versus bivalve occurrences is correlated with the stage-level sampling probabilities of aragonitic versus calcitic taxa. Average sampling probabilities are higher for calcitic species, but this contrast is time-varying in a predictable way, being concentrated in stages with widespread carbonate deposition.To understand these results fully, we link them with analyses at the level of individual point occurrences. Doing so reveals that aragonite bias is effectively absent in terrigenous clastic sediments. In limestones, by contrast, calcitic species have at least twice the odds of sampling as aragonitic species. This result is most pronounced during times of widespread carbonate deposition, where the difference in the per-collection odds of sampling species is a factor of eight. During carbonate-rich intervals, calcitic taxa also have higher odds of sampling in clastics. At first glance this result may suggest simple preservational bias against aragonite. However, comparing relative odds of aragonitic versus calcitic sampling with absolute sampling rates shows that the positive calcite bias during carbonate-rich times reflects higher than average occurrence rates for calcitic taxa (rather than lower rates for aragonitic taxa) and that the negative aragonite bias in limestones reflects lower than average occurrence rates for aragonitic taxa (rather than higher rates for calcitic taxa).Our results therefore indicate a time-varying interplay of two main factors: (1) taphonomic loss of aragonitic species in carbonate sediments, with no substantial bias in terrigenous clastics; and (2) an ecological preference of calcitic taxa for environments characteristic of periods with pervasive carbonate deposition, irrespective of lithology per se.
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Langer, G., G. Nehrke, C. Baggini, R. Rodolfo-Metalpa, J. M. Hall-Spencer, and J. Bijma. "Limpets counteract ocean acidification induced shell corrosion by thickening of aragonitic shell layers." Biogeosciences 11, no. 24 (December 20, 2014): 7363–68. http://dx.doi.org/10.5194/bg-11-7363-2014.
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Abstract. Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells) and outside (pHn-shells) a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size-normalised aragonite area. Size-normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size-normalised thickness of the pHlow-shells, these data led us to conclude that low-pH-exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. This is different from normal elongation growth and proceeds through addition of aragonitic parts only, while the production of calcitic parts is confined to elongation growth. Therefore, aragonite cannot be regarded as a disadvantageous polymorph per se under ocean acidification conditions.
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Langer, G., G. Nehrke, C. Baggini, R. Rodolfo-Metalpa, J. Hall-Spencer, and J. Bijma. "Limpets counteract ocean acidification induced shell corrosion by thickening of aragonitic shell layers." Biogeosciences Discussions 11, no. 8 (August 25, 2014): 12571–90. http://dx.doi.org/10.5194/bgd-11-12571-2014.
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Abstract. Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells) and outside (pHn-shells) a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size normalised aragonite area. Size normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size normalised thickness of the pHlow-shells, these data led us to conclude that low pH exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. The latter is different from normal elongation growth and proceeds through addition of aragonitic layers only, while the production of calcitic layers is confined to elongation growth. Therefore aragonite cannot be regarded as a per se disadvantageous polymorph under ocean acidification conditions.
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Lin, Yongjie, Ian M. Power, and Wenxi Chen. "Holocene Lacustrine Abiotic Aragonitic Ooids from the Western Qaidam Basin, Qinghai-Tibetan Plateau." Minerals 12, no. 11 (October 31, 2022): 1400. http://dx.doi.org/10.3390/min12111400.
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Carbonate ooids are a significant component of shallow water carbonate deposits in the present and geologic past, yet their origin and formation mechanism have been the subject of continuing debate. This study focuses on the well-preserved Holocene aragonitic ooids in west Qaidam Basin, western Qinghai-Tibetan Plateau (QTP). The mineralogical and chemical compositions, and stable (δ13C and δ18O), and radiocarbon isotopes of the ooids were analyzed to investigate their origin and formation mechanism. AMS radiocarbon dating of samples indicates that the exact dates of ooid formation is around 5377±61 cal BP. The ooid of cortices was composed of microcrystalline aragonite, with most nuclei being quartz grains. Stable carbon and oxygen isotopes indicate that authigenic aragonite precipitation is driven by evaporation and associated degassing of CO2 under turbulence conditions in shallow alkaline lakes. Furthermore, microscopy showed no presence of microfossils in ooid cortices or other evidence of microbial activity. We propose that aragonite precipitation during ooid formation is most likely induced abiotically by increasing alkalinity due to evapoconcentration of lake waters based on an absence of an efficient carbonate-inducing metabolic pathway. New observations and detailed analyses of aragonitic ooid samples in the Qaidam Basin provide an improved understanding of the origin and formation processes of carbonate ooid in the present and geologic past.
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Stein, Mordechai, Boaz Lazar, and Steven L. Goldstein. "Radiocarbon Reservoir Ages as Freshwater-Brine Monitors in Lake Lisan, Dead Sea System." Radiocarbon 55, no. 2 (2013): 1050–57. http://dx.doi.org/10.1017/s0033822200058185.
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A continuous and high-resolution record of the radiocarbon reservoir age (RA) has been recovered from the primary aragonites that were deposited from the last glacial Lake Lisan. The RA is calculated as the difference between the measured 14C “apparent” age in the aragonite and the atmospheric age at any particular time. The RA shows temporal decreases during the time interval of ≃28 to ≃18 ka cal BP. This behavior is attributed to a continuous addition of low RA-high bicarbonate freshwater into the high RA-Ca-chloride (low bicarbonate) brine solution filling the lake. The mixing of the brine with freshwater drives the precipitation of CaCO3 in the form of aragonite from the lake epilimnion (surface layer). The runoff-brine mixture in Lake Lisan is also reflected by the Sr/Ca ratios that are positively correlated with the RA. Nevertheless, the 14C content in the epilimnion did not drop at the same rate as the atmospheric value but rather remained nearly constant. We suggest that turbulent mixing with the much saltier hypolimnion (lower layer) across the hypolimnion/epilimnion interface at a depth of about 390 m below sea level, buffered the 14C content as well as the Sr and Ca concentrations in the aragonite precipitating solution. The RA-Sr/Ca related limnological model developed here opens the way to determine the reservoir-age-corrected atmospheric ages of Lisan Formation aragonites beyond 28 ka cal BP.
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Morad, Tzachy, Roni Mina Hendler, Eyal Canji, Orly Eva Weiss, Guy Sion, Refael Minnes, Ania Hava Grushchenko Polaq, et al. "Aragonite-Polylysine: Neuro-Regenerative Scaffolds with Diverse Effects on Astrogliosis." Polymers 12, no. 12 (November 29, 2020): 2850. http://dx.doi.org/10.3390/polym12122850.
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Biomaterials, especially when coated with adhesive polymers, are a key tool for restorative medicine, being biocompatible and supportive for cell adherence, growth, and function. Aragonite skeletons of corals are biomaterials that support survival and growth of a range of cell types, including neurons and glia. However, it is not known if this scaffold affects neural cell migration or elongation of neuronal and astrocytic processes, prerequisites for initiating repair of damage in the nervous system. To address this, hippocampal cells were aggregated into neurospheres and cultivated on aragonite skeleton of the coral Trachyphyllia geoffroyi (Coral Skeleton (CS)), on naturally occurring aragonite (Geological Aragonite (GA)), and on glass, all pre-coated with the oligomer poly-D-lysine (PDL). The two aragonite matrices promoted equally strong cell migration (4.8 and 4.3-fold above glass-PDL, respectively) and axonal sprouting (1.96 and 1.95-fold above glass-PDL, respectively). However, CS-PDL had a stronger effect than GA-PDL on the promotion of astrocytic processes elongation (1.7 vs. 1.2-fold above glass-PDL, respectively) and expression of the glial fibrillary acidic protein (3.8 vs. and 1.8-fold above glass-PDL, respectively). These differences are likely to emerge from a reaction of astrocytes to the degree of roughness of the surface of the scaffold, which is higher on CS than on GA. Hence, CS-PDL and GA-PDL are scaffolds of strong capacity to derive neural cell movements and growth required for regeneration, while controlling the extent of astrocytic involvement. As such, implants of PDL-aragonites have significant potential as tools for damage repair and the reduction of scar formation in the brain following trauma or disease.
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Grant, S. W. F., A. H. Knoll, and G. J. B. Germs. "Probable calcified metaphytes in the latest Proterozoic Nama Group, Namibia: origin, diagenesis, and implications." Journal of Paleontology 65, no. 1 (January 1991): 1–18. http://dx.doi.org/10.1017/s002233600002014x.
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Samples from the Huns Limestone Member, Urusis Formation, Nama Group, at two adjacent localities in southern Namibia contain thin foliose to arched, sheet-like carbonate crusts that are 100–500 µm thick and up to 5 cm in lateral dimension. Morphologic, petrographic, and geochemical evidence supports the interpretation of these delicate crusts as biogenic, most likely the remains of calcified encrusting metaphytes. The original sediments of the fossiliferous samples contained aragonitic encrusting algae, botryoidal aragonite cements, and an aragonite mud groundmass. Spherulites within the precursor mud could represent bacterially induced mineral growths or the concretions of marine rivularian cyanobacteria. Original textures were severely disrupted during the diagenetic transition of aragonite to low-magnesian calcite, but some primary structures remain discernible as ghosts in the neomorphic mosaic. Gross morphology, original aragonite mineralogy, and hypobasal calcification indicate that the crusts are similar to late Paleozoic phylloid algae and extant peyssonnelid red algae. Structures interpreted as possible conceptacles also suggest possible affinities with the Corallinaceae.Two species of Cloudina, interpreted as the remains of a shelly metazoan, are also known from limestones in the Nama Group. It is possible, therefore, that skeletalization in metaphytes and animals arose nearly simultaneously near the end of the Proterozoic Eon.
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Casella, Laura A., Erika Griesshaber, Xiaofei Yin, Andreas Ziegler, Vasileios Mavromatis, Dirk Müller, Ann-Christine Ritter, et al. "Experimental diagenesis: insights into aragonite to calcite transformation of <i>Arctica islandica</i> shells by hydrothermal treatment." Biogeosciences 14, no. 6 (March 24, 2017): 1461–92. http://dx.doi.org/10.5194/bg-14-1461-2017.
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Abstract. Biomineralised hard parts form the most important physical fossil record of past environmental conditions. However, living organisms are not in thermodynamic equilibrium with their environment and create local chemical compartments within their bodies where physiologic processes such as biomineralisation take place. In generating their mineralised hard parts, most marine invertebrates produce metastable aragonite rather than the stable polymorph of CaCO3, calcite. After death of the organism the physiological conditions, which were present during biomineralisation, are not sustained any further and the system moves toward inorganic equilibrium with the surrounding inorganic geological system. Thus, during diagenesis the original biogenic structure of aragonitic tissue disappears and is replaced by inorganic structural features. In order to understand the diagenetic replacement of biogenic aragonite to non-biogenic calcite, we subjected Arctica islandica mollusc shells to hydrothermal alteration experiments. Experimental conditions were between 100 and 175 °C, with the main focus on 100 and 175 °C, reaction durations between 1 and 84 days, and alteration fluids simulating meteoric and burial waters, respectively. Detailed microstructural and geochemical data were collected for samples altered at 100 °C (and at 0.1 MPa pressure) for 28 days and for samples altered at 175 °C (and at 0.9 MPa pressure) for 7 and 84 days. During hydrothermal alteration at 100 °C for 28 days most but not the entire biopolymer matrix was destroyed, while shell aragonite and its characteristic microstructure was largely preserved. In all experiments up to 174 °C, there are no signs of a replacement reaction of shell aragonite to calcite in X-ray diffraction bulk analysis. At 175 °C the replacement reaction started after a dormant time of 4 days, and the original shell microstructure was almost completely overprinted by the aragonite to calcite replacement reaction after 10 days. Newly formed calcite nucleated at locations which were in contact with the fluid, at the shell surface, in the open pore system, and along growth lines. In the experiments with fluids simulating meteoric water, calcite crystals reached sizes up to 200 µm, while in the experiments with Mg-containing fluids the calcite crystals reached sizes up to 1 mm after 7 days of alteration. Aragonite is metastable at all applied conditions. Only a small bulk thermodynamic driving force exists for the transition to calcite. We attribute the sluggish replacement reaction to the inhibition of calcite nucleation in the temperature window from ca. 50 to ca. 170 °C or, additionally, to the presence of magnesium. Correspondingly, in Mg2+-bearing solutions the newly formed calcite crystals are larger than in Mg2+-free solutions. Overall, the aragonite–calcite transition occurs via an interface-coupled dissolution–reprecipitation mechanism, which preserves morphologies down to the sub-micrometre scale and induces porosity in the newly formed phase. The absence of aragonite replacement by calcite at temperatures lower than 175 °C contributes to explaining why aragonitic or bimineralic shells and skeletons have a good potential of preservation and a complete fossil record.
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Mastandrea, A., and F. Russo. "Microstructure and diagenesis of calcified demosponges from the Upper Triassic of the northeastern Dolomites (Italy)." Journal of Paleontology 69, no. 3 (May 1995): 416–31. http://dx.doi.org/10.1017/s002233600003482x.
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The calcareous skeletons of 17 species of Triassic demosponges from the northeastern Dolomites have been analyzed for microstructure and diagenesis. The four microstructures recognized (irregular, spherulitic, penicillate aragonitic, and homogeneous granular Mg calcite) are described in terms of mineralogy; shape, dimension, and arrangement of microstructural elements; mode of growth; and possible biomineralization. The diagenesis in these sponge carbonate skeletons is of an aggrading type that occurred in diagenetic units, semi-closed systems, delineated by organic phragmas, which controlled the flux of diagenetic fluids. We tentatively interpret these phragmas as the remains of water-insoluble macromolecules for space delineation during the biomineralization process. In the aragonitic skeletons the preservation grade is correlated with Sr content, and the replacement of aragonite by calcite is marked by a Sr value around 4,000 p.p.m. Calcitized aragonite still retains a detectable amount of Sr. In Mg calcite skeletons the continuous and regular increase of grain size is inversely correlated with Mg content and directly with the distance from the organic phragmas.
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Perrin, Christine. "Early diagenesis of carbonate biocrystals : isomineralogical changes in aragonite coral skeletons." Bulletin de la Société Géologique de France 175, no. 2 (March 1, 2004): 95–106. http://dx.doi.org/10.2113/175.2.95.
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Abstract Early diagenetic changes occurring in aragonite coral skeletons were characterized at the micro- and ultra-structural scales in living and fossil scleractinian colonies, the latter of Pleistocene age. The skeleton of scleractinian corals, like all biomineralized structures, is a composite material formed by the intimate association of inorganic aragonite crystallites and organic matrices. In addition to its organo-mineral duality, the scleractinian skeleton is formed by the three-dimensional arrangement of two clearly distinct basic structural features, the centers of calcification and the fibers. The latter are typically characterized by a transverse micron-scale zonation revealing their incremental growth process. The size, geometry and three-dimensional arrangement of calcification centers and fibers are taxon-specific. The earliest diagenetic modifications of these skeletons have been clearly recognized in the older parts of living colonies. The first steps of diagenesis therefore take place only a few years after the skeleton had been secreted by the living polyps, and in the same environmental conditions. Comparisons with the uppermost living parts of the coral colonies clearly show that these first diagenetic changes are driven by the biological ultrastructural characteristics of these skeletons and are conditioned by the presence of organic envelopes interbedded with and surrounding aragonite crystallites. These first diagenetic processes induce the development of thin fringes of fibrous aragonite cements growing syntaxially on the aragonitic coral fibers, an alteration of the incremental zonation of coral fibers and also preferential diagenetic changes in the calcification centers, including dissolution of their minute internal crystals. Diagenetic patterns observed in Pleistocene coral colonies typically involve the same processes already recognized in the older skeletal parts of living colonies, suggesting that diagenesis occurs through continuous processes instead of clearly differentiated stages. Selective dissolution affects calcification centers and some growth increments of coral fibers. Alteration of the initial transverse zonation of coral fibers also occur through the development of micro-inclusions clearly seen in ultra-thin sections. Although usually thicker than those observed in the ancient skeletal parts of living colonies, syntaxial aragonite cements commonly occur in these fossil skeletons. These cements are often associated with gradual textural modifications of the underlying coral fibers, in particular the loss of the transverse micron-scale zonation. This suggests that the coral skeleton forming the substratum of diagenetic cements is progressively recrystallized in secondary aragonite. This recrystallization of coral aragonite begins at the external margin of the skeleton, just below the diagenetic cements and gradually moves towards the internal skeletal parts. Recrystallization takes place through concomitant fine-scale dissolution-precipitation processes and occurs with textural changes but no mineralogical change. The process of recrystallization is likely initiated by a biological degradation of organic skeletal matrices and can be also driven by thermodynamical constraints involving the lowering of surface free energies resulting from changes in crystal size. Alteration of skeletal organic matrix, textural changes in coral biocrystals through recrystallization and precipitation of secondary diagenetic aragonite may bias the original geochemical characteristics of coral skeletons. Although more work is needed to establish the influence of these early diagenetic processes on the geochemical signatures, it is already well known that the breakdown of organic skeletal envelopes and early recrystallization of shallow-water carbonates alter the stable isotopic composition. The widespread use of coral skeletons as environmental and climatic proxies makes strongly necessary a better understanding of these early diagenetic mechanisms and a precise characterization of the fine-scale diagenetic patterns of specimens for the optimization of geochemical interpretations. In particular, it cannot be assumed that an entire aragonitic composition can guarantee that there is no or slight diagenetic alteration.
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Wu, Wenlong, Liping Zhang, Zhijun Yang, and Weisheng Hou. "Study on the Microstructure of the Pinctada martensii Pearls and Its Significance." ISRN Spectroscopy 2012 (July 16, 2012): 1–9. http://dx.doi.org/10.5402/2012/756217.
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The results of a microscopy, SEM-EDS, XRD, FTIR, and Raman spectra study of the nacres of the Pinctada martensii pearls from Zhanjiang city, China shows that they can be classified as the high-quality, medium-quality, and inferior-quality pearls. Aragonite, the main inorganic mineralogy in the nacres, was crystallized and grown up in the compartments formed by the silk and radial organic sheets originating from organic matters secreted by the mantle of mollusks. The crystalline orientations of aragonite tablets were changed from the (002), (012) and (102) crystalline plane nets in the early to the (002) crystalline plane net only in the later. The formation processes of the microstructure of the nacres could be divided into three stages. In the early stage, the precursor particles of aragonite nucleated and grew up fast; then, porous aragonite aggregates consisting of the fine aragonite crystals were formed. In the middle stage, the aragonite crystals directionally grew up to form the aragonite tablets and microlayers. The surface of the aragonite tablets and microlayers are rough and few porous, and the edges of the crystals were serrated. In the last stage, the aragonite tablets in the aragonite microlayer mixed perfectly together to form high-quality aragonite layer whose surface was smooth and perfect.
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Gangstø, R., M. Gehlen, B. Schneider, L. Bopp, O. Aumont, and F. Joos. "Modeling the marine aragonite cycle: changes under rising carbon dioxide and its role in shallow water CaCO<sub>3</sub> dissolution." Biogeosciences 5, no. 4 (July 28, 2008): 1057–72. http://dx.doi.org/10.5194/bg-5-1057-2008.
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Abstract. The marine aragonite cycle has been included in the global biogeochemical model PISCES to study the role of aragonite in shallow water CaCO3 dissolution. Aragonite production is parameterized as a function of mesozooplankton biomass and aragonite saturation state of ambient waters. Observation-based estimates of marine carbonate production and dissolution are well reproduced by the model and about 60% of the combined CaCO3 water column dissolution from aragonite and calcite is simulated above 2000 m. In contrast, a calcite-only version yields a much smaller fraction. This suggests that the aragonite cycle should be included in models for a realistic representation of CaCO3 dissolution and alkalinity. For the SRES A2 CO2 scenario, production rates of aragonite are projected to notably decrease after 2050. By the end of this century, global aragonite production is reduced by 29% and total CaCO3 production by 19% relative to pre-industrial. Geographically, the effect from increasing atmospheric CO2, and the subsequent reduction in saturation state, is largest in the subpolar and polar areas where the modeled aragonite production is projected to decrease by 65% until 2100.
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Deo Singh, Arun. "Centennial to millennial-scale changes in thermocline ventilation in the Arabian Sea: insights from the pteropod preservation record." Journal of Palaeosciences 70, no. (1-2) (September 10, 2021): 253–66. http://dx.doi.org/10.54991/jop.2021.18.
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The Arabian Sea hosts one of the three thickest oxygen minimum zones (OMZs) of the world ocean. Mid–depth oxygen depletion profoundly influences the chemistry of thermocline waters (HCO3 ˉ, CO3 2 ˉ and pH), which in turn significantly influences the preservation state of carbonates. The carbonate preservation is primarily controlled by the degree of saturation level of seawater with respect to the calcite and aragonite. The seawater in OMZ is undersaturated with respect to the aragonite (a metastable polymorph of CaCO3). Pteropod test being aragonitic in composition is therefore highly susceptible to the dissolution and dissolves completely below the aragonite compensation depth (ACD). Because of the current condition of intense OMZ due to high primary productivity, enhanced respiration of sinking organic carbon and reduced thermocline circulation; the ACD is shallow, lying in the middle of the OMZ. Hence, preservation record of pteropods in sea–floor sediment archives past changes in thermocline oxygen condition, carbonate chemistry, the ACD and OMZ intensity. High resolution records of various pteropod preservation indices (total pteropod abundance, transparent Limacina inflata abundance, fragmentation index) in a sediment core from the lower OMZ of the Indian margin (off Goa) enabled to investigate aragonite preservation/dissolution events and their links with the changes in ACD and OMZ intensity in the eastern Arabian Sea during the last 70 kyr BP. The proxy records reveal centennial to millennial scale changes in aragonite preservation condition in concert with Northern Hemisphere climatic events (Dansgaard–Oeschger (D–O) cycles and Heinrich events). The pteropod preservation spikes apparently correspond to the Northern Hemisphere cold events (D–O stadials and Heinrich events). Whereas, the pteropod tests were either poorly preserved or completely dissolved during the warm phases of D–O cycles (interstadials). The aragonite preservation events are attributed to the low monsoon induced productivity combined with the increased thermocline ventilation by Subantarctic Mode and Antarctic Intermediate Waters (SAMW–AAIW) resulting a weak OMZ and deeper ACD. The novel proxies (abundances of Globorotalia menardii, a planktic foraminifera and Styliola subula, a pteropod species) are used to gain better insights in to the variability of thermocline ventilation and OMZ intensity through time.
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Németh, Péter, Enrico Mugnaioli, Mauro Gemmi, György Czuppon, Attila Demény, and Christoph Spötl. "A nanocrystalline monoclinic CaCO3precursor of metastable aragonite." Science Advances 4, no. 12 (December 2018): eaau6178. http://dx.doi.org/10.1126/sciadv.aau6178.
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Despite its thermodynamical metastability at near-surface conditions, aragonite is widespread in marine and terrestrial sediments. It abundantly forms in living organisms, and its abiotic formation is favored in waters of a Mg2+/Ca2+ratio > 1.5. Here, we provide crystallographic evidence of a nanocrystalline CaCO3polymorph, which precipitates before aragonite in a cave. The new phase, which we term monoclinic aragonite (mAra), is crystallographically related to ordinary, orthorhombic aragonite. Electron diffraction tomography combined with structure determination demonstrates that mAra has a layered aragonite structure, in which some carbonates can be replaced by hydroxyls and up to 10 atomic % of Mg can be incorporated. The diagnostic electron diffraction features of mAra are diffuse scattering and satellite reflections along aragonite {110}. Similar features have previously been reported—although unrecognized—from biogenic aragonite formed in stromatolites, mollusks, and cyanobacteria as well as from synthetic material. We propose that mAra is a widespread crystalline CaCO3that plays a hitherto unrecognized key role in metastable aragonite formation.
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Gangstø, R., M. Gehlen, B. Schneider, L. Bopp, O. Aumont, and F. Joos. "Modeling the marine aragonite cycle: changes under rising carbon dioxide and its role in shallow water CaCO<sub>3</sub> dissolution." Biogeosciences Discussions 5, no. 2 (April 16, 2008): 1655–87. http://dx.doi.org/10.5194/bgd-5-1655-2008.
Full textAbstract:
Abstract. The marine aragonite cycle has been included in the global biogeochemical model PISCES to study the role of aragonite in shallow water CaCO3 dissolution. Aragonite production is parameterized as a function of mesozooplankton biomass and aragonite saturation state of ambient waters. Observation-based estimates of marine carbonate production and dissolution are well reproduced by the model and about 60% of the combined CaCO3 water column dissolution from aragonite and calcite is simulated above 2000 m. In contrast, a calcite-only version yields a much smaller fraction. This suggests that the aragonite cycle should be included in models for a realistic representation of CaCO3 dissolution and alkalinity. For the SRES A2 CO2 scenario, production rates of aragonite are projected to notably decrease after 2050. By the end of this century, global aragonite production is reduced by almost one third and total CaCO3 production by 19% relative to pre-industrial. Geographically, the effect from increasing atmospheric CO2, and the subsequent reduction in saturation state, is largest in the subpolar and polar areas where the modeled aragonite production is projected to decrease by 65% until 2100.
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Chen, Bin, Ji Luo, Quan Yuan, and Jing Hong Fan. "Mechanism of High Modulus and Strength of Unio Douglasiae Shell." Key Engineering Materials 467-469 (February 2011): 571–74. http://dx.doi.org/10.4028/www.scientific.net/kem.467-469.571.
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Scanning electron microscope (SEM) observation shows that the shell of a Unio douglasiae is a kind of bioceramic composite consisting of laminated aragonite and organic materials. The aragonite layers further consist of thin and long aragonite fibers. The aragonite fibers possess high density in the shell and their diameter is within nanometer scale. The mechanism of the high modulus and high strength of the shell were investigated based on the observed nanometer structure of the aragonite fibers and the rule of mixtures Young’s modulus as well as the Griffith criterion. It reveals that the high density and the nanometer scale of the aragonite fibers endow the shell with high modulus and fracture strength.
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Chen, Bin, Xiang He Peng, and Shi Tao Sun. "Research on the Curving Aragonite Sheets in Clam’s Shell." Key Engineering Materials 361-363 (November 2007): 475–78. http://dx.doi.org/10.4028/www.scientific.net/kem.361-363.475.
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Molluscan shell possesses excellent strength, stiffness and fracture toughness that are closely related to its exquisite microstructure. SEM observation of a clam’ shell showed that the shell is a kind of bioceramic composite consisting of aragonite and protein layers parallel with the surface of the shell. The observation also showed that the aragonite layers are composed of long and thin aragonite sheets. Many aragonite sheets are of curving shape at the center of the shell. The higher fracture toughness of the shell was analyzed based on the representative model of the curving aragonite sheets and the concept of the maximum pullout force that is related to the fracture toughness of the shell. The analytical result showed that the maximum pullout force of the curving aragonite sheet is larger than that of straight aragonite sheets, which may effectively enhance the fracture toughness of the shell.
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Chen, Bin, Xiang He Peng, and Xin Yan Wu. "Research of Herringbone Structure of Fragum Unedo Shell." Key Engineering Materials 330-332 (February 2007): 1273–76. http://dx.doi.org/10.4028/www.scientific.net/kem.330-332.1273.
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The microstructure of a Fragum unedo shell is observed with a scanning electronic microscope (SEM). It shows that the shell is a kind of bio-ceramic composite consisting of aragonite and collagen protein layers. The observation also shows that the aragonite layers consist of thin and long aragonite sheets. A kind of particular herringbone structure of the aragonite sheets is found. In the structure, the aragonite sheets in an arbitrary aragonite layer make a crossed angle against that in its neighboring aragonite layers. Based on the SEM observation the comparative experiments in the maximum pull-out forces of both the herringbone and conventional 0°-structures are conducted. It shows that the maximum pull-out force of the herringbone structure is markedly larger than that of the 0°-structure, and the larger the crossed angle is, the more the maximum pull-out force of the herringbone structure will increase compared with that of the 0°-structure.
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Kellock, Celeste, Maria Cristina Castillo Alvarez, Adrian Finch, Kirsty Penkman, Roland Kröger, Matthieu Clog, and Nicola Allison. "Optimising a method for aragonite precipitation in simulated biogenic calcification media." PLOS ONE 17, no. 12 (December 2, 2022): e0278627. http://dx.doi.org/10.1371/journal.pone.0278627.
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Resolving how factors such as temperature, pH, biomolecules and mineral growth rate influence the geochemistry and structure of biogenic CaCO3, is essential to the effective development of palaeoproxies. Here we optimise a method to precipitate the CaCO3 polymorph aragonite from seawater, under tightly controlled conditions that simulate the saturation state (Ω) of coral calcification fluids. We then use the method to explore the influence of aspartic acid (one of the most abundant amino acids in coral skeletons) on aragonite structure and morphology. Using ≥200 mg of aragonite seed (surface area 0.84 m2), to provide a surface for mineral growth, in a 330 mL seawater volume, generates reproducible estimates of precipitation rate over Ωaragonite = 6.9–19.2. However, unseeded precipitations are highly variable in duration and do not provide consistent estimates of precipitation rate. Low concentrations of aspartic acid (1–10 μM) promote aragonite formation, but high concentrations (≥ 1 mM) inhibit precipitation. The Raman spectra of aragonite precipitated in vitro can be separated from the signature of the starting seed by ensuring that at least 60% of the analysed aragonite is precipitated in vitro (equivalent to using a seed of 200 mg and precipitating 300 mg aragonite in vitro). Aspartic acid concentrations ≥ 1mM caused a significant increase in the full width half maxima of the Raman aragonite v1 peak, reflective of increased rotational disorder in the aragonite structure. Changes in the organic content of coral skeletons can drive variations in the FWHM of the Raman aragonite ν1 peak, and if not accounted for, may confuse the interpretation of calcification fluid saturation state from this parameter.
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Brown, Alastair. "Aragonite shell damage." Nature Climate Change 3, no. 1 (December 21, 2012): 15. http://dx.doi.org/10.1038/nclimate1797.
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Guth, Alexandria L. "Aragonite: Mistaken Identities." Rocks & Minerals 85, no. 5 (August 13, 2010): 456–58. http://dx.doi.org/10.1080/00357521003727298.
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Pohwat, Paul W. "Connoisseur's Choice: Aragonite." Rocks & Minerals 90, no. 2 (March 3, 2015): 164–75. http://dx.doi.org/10.1080/00357529.2015.997155.
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Dauphin, Y. "Infrared Spectra and Elemental Composition in Recent Carbonate Skeletons: Relationships between the ν2 Band Wavenumber and Sr and Mg Concentrations." Applied Spectroscopy 51, no. 2 (February 1997): 253–58. http://dx.doi.org/10.1366/0003702971940152.
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Biological aragonites show various chemical compositions (Sr and Mg) related to the systematic position of the organisms. It is well known that Cnidaria tests have high Mg and Sr aragonites, whereas Mollusca shells have low Mg and Sr aragonites. Sponges have low Mg and high Sr aragonites. The linear correlation between Mg and Sr concentrations is positive. DRIFT spectra show that the wavenumber of a part of the doublet ν2 significantly differs in the Mollusca shells and the Sponges and Cnidaria set: 863.7 cm−1 in Mollusca, 858.8 cm−1 in Sponges + Cnidaria. The other part of the doublet is similar in the two sets (844.1 cm−1). ν1 and the doublet ν4 do not seem to be altered. There is a strong linear correlation between the ν2 wavenumber and the Mg and Sr concentrations in these biological aragonites. It is known that the calcite–aragonite transition apparently shifts the wavenumber of ν2, but such a shift has not been observed in one mineral.
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Park, Woon Kyoung, Ji Whan Ahn, Sang Jin Ko, and Choon Han. "Crystal Growth of Aragonite Precipitated Calcium Carbonate by Seeded Method." Materials Science Forum 544-545 (May 2007): 693–96. http://dx.doi.org/10.4028/www.scientific.net/msf.544-545.693.
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Characteristics of nucleation and crystal growth of aragonite precipitated calcium carbonate in Ca(OH)2 – MgCl2 – CO2 system via a carbonation process is investigated. Aragonite precipitated calcium carbonate with high aspect ratio was synthesized at high reaction temperature and concentration of Ca(OH)2 slurry. The increase in crystal size with decreased in CO2 gas flow rate can be explained by a decrease in the nucleation rate and an increase in the crystal growth rate caused by a decrease in the dissolution rate to CO3 2- ion. In this study, crystal growth of aragonite was investigated by adding aragonite seed. It was found that crystal growth of aragonite precipitated calcium carbonate could be controlled by three-step carbonation process using reactants as the Ca(OH)2. Aragonite with an aspect ratio from 5 to 27 and diameter from 3μm to 24μm was thereby grown at a reaction temperature of 80°C and a CO2 flow rate of 50ml/min. It was also found that MgCl2 aqueous solution can be used again in the carbonation process for the synthesis of aragonite precipitated calcium carbonate.
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Huang, Zeng-Qiong, Gang-Sheng Zhang, and Yuan Tan. "Gelatinous Siphon Sheath Templates the Starfruit-Shaped Aragonite Aggregate Growth." Journal of Nanomaterials 2019 (February 10, 2019): 1–9. http://dx.doi.org/10.1155/2019/7328478.
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Biomimetic synthesis of aragonite with various templates in vitro is an important way to understand the biomineralization process and synthesize nacre-like materials. Herein, we used the siphon sheath from the bivalve Lutraria sieboldii as the substrate for the formation of calcium carbonate. We found that the inner layer of the sheath, which is composed of approximately 40% protein and 60% β-chitin, induced the formation of nearly pure aragonite by the transformation of amorphous calcium carbonate (ACC). More surprisingly, unique starfruit-shaped aragonite aggregates were observed on the substrate and were constructed from many adhered, oriented aragonite tablets. We consider that the acid-rich protein from the inner layer of the siphon sheath triggers the formation of ACC, and the swollen β-chitin regulates the transformation of ACC into aragonite by lattice matching and stereochemical recognition. The various surface adhesion energies of the crystal, the change in growth rates on different crystallographic facets, and the hexagonal features of the aragonite tablets led to the formation of starfruit-shaped aragonite aggregates.
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Koleva-Rekalova, Elena. "Sarmatian aragonite sediments in North-eastern Bulgaria - origin and diagenesis." Geologica Balcanica 24, no. 5 (October 30, 1994): 47–64. http://dx.doi.org/10.52321/geolbalc.24.5.47.
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Unconsolidated aragonite sediments of Bessarabian – Chersonian age (Middle – Late Sarmatian), are established for the first time in the Topola Formation (North-Eastern Bulgaria). The aragonite crystals amount to 85-95% of the rock volume, and are considered as a product of chemical precipitation. The term “aragonitites” is proposed for the unconsolidated aragonite sediments. Aragonitites predominate over the consolidated carbonate rocks (micritic limestones and dolomites) in the studied sections. Clay interbeds are also identified. The deposition of the primary aragonite muds took place in a small shallow bay, opened to the south-southeast, in condition of arid climate. Periodic lithification of a part of the aragonite muds proceeded as a result of neomorphic processes – aragonite transformation to low-magnesian calcite, recrystallization of calcite to coarser one, and further dolomitization. An attempt is made to prove that lithification had place under submarine and brackish conditions.
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Chen, Bin, Shi Tao Sun, Xiang He Peng, and Jing Hong Fan. "Investigation on Screwy Microstructure of Solid-Trough Shell." Key Engineering Materials 396-398 (October 2008): 453–56. http://dx.doi.org/10.4028/www.scientific.net/kem.396-398.453.
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Scanning electron microscope (SEM) observation shows that Solid-trough shell is a kind of bioceramic composite consisting of laminated aragonite and organic materials. The aragonite layers are parallel with the surface of the shell and consist of numerous thin and long aragonite fibers. The aragonite fibers in an arbitrary aragonite layers possess different directions and compose a kind of screwy microstructure. The maximum pullout force of the screwy microstructure was investigated and compared with that of parallel microstructure based on their representative models. It shows that the maximum pullout force of the screwy microstructure is markedly larger than that of the parallel microstructure, which was experimentally validated.
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Fellner, Pavel, Jana Jurišová, Jana Kozánková, and Ladislav Pach. "Preparation of needle-like aragonite particles from calcium nitrate solution in batch and flow reactors." Acta Chimica Slovaca 5, no. 1 (April 1, 2012): 5–11. http://dx.doi.org/10.2478/v10188-012-0001-7.
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Preparation of needle-like aragonite particles from calcium nitrate solution in batch and flow reactors Needle-like aragonite particles for application in paper industry were synthesised from calcium nitrate solution. Calcium nitrate was prepared from waste lime. Samples of precipitated aragonite were prepared both in batch and flow reactors, respectively. Conditions (concentration of calcium nitrate, temperature, and flow rate of CO2) were optimized for achieving high yield of aragonite in the product.
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Renaut, Rubin W., and Brian Jones. "Controls on aragonite and calcite precipitation in hot spring travertines at Chemurkeu, Lake Bogoria, Kenya." Canadian Journal of Earth Sciences 34, no. 6 (June 1, 1997): 801–18. http://dx.doi.org/10.1139/e17-066.
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Subfossil travertines precipitated around hot spring orifices at Chemurkeu on the western shore of Lake Bogoria, Kenya, are composed of calcite, aragonite, and minor dolomite. Aragonite crystal beds, which form 5–10% of the travertine by volume, are formed of large pseudohexagonal prisms, whereas the calcite crystal beds are composed mainly of feather dendrites. Dolomite is only found between aragonite crystals. Boundaries between aragonite and calcite crystals commonly display evidence of dissolution, but there is no evidence to indicate that calcite formed by inversion of aragonite or that the dolomite replaced the aragonite. Thus, the aragonite, calcite, and dolomite are each treated as primary precipitates. Reticulate gelatinous coatings, with a high Si and Mg content, cover most external and internal surfaces of the aragonite and calcite crystals. The travertines may have formed under more humid conditions than today, when the spring waters contained more Ca2+. The physiochemical conditions at the modern springs provide a context for interpreting the factors that controlled the precipitation of the aragonite and calcite. Today, the hot (T > 85 °C) Na–HCO3–Cl spring waters at Chemurkeu, which have a salinity of ~6 g∙L−1 total dissolved solids, a pH of 8.1–9.1, and contain < 2 mg∙L−1 of Ca2+ and < 0.7 mg∙L−1 of Mg2+, are fed by a shallow aquifer [Formula: see text] and a deeper aquifer (T = 170 °C). Modern spring waters, derived from meteoric groundwater, lake water, and condensed steam, are fed mainly from the shallow thermal aquifer. Field, petrographic, and scanning electron microscope evidence obtained from the travertines, coupled with knowledge of the modern springs, indicates that the progressive and cyclic alternation from calcite precipitation to aragonite precipitation to aragonite dissolution which characterizes many travertine successions may have been caused by changes in [Formula: see text] of the spring waters under high temperatures (> 90 °C). The textures in the travertines show that precipitation of the aragonite and calcite crystals was probably abiotic, and episodic rather than continuous. Rapid degassing of CO2 associated with shallow boiling was probably a major factor in crystal growth.
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Islam, Kh Nurul, A. B. Z. Zuki, M. E. Ali, Mohd Zobir Bin Hussein, M. M. Noordin, M. Y. Loqman, H. Wahid, M. A. Hakim, and Sharifa Bee Abd Hamid. "Facile Synthesis of Calcium Carbonate Nanoparticles from Cockle Shells." Journal of Nanomaterials 2012 (2012): 1–5. http://dx.doi.org/10.1155/2012/534010.
Full textAbstract:
A simple and low-cost method for the synthesis of calcium carbonate nanoparticles from cockle shells was described. Polymorphically, the synthesized nanoparticles were aragonites which are biocompatible and thus frequently used in the repair of fractured bone and development of advanced drug delivery systems, tissue scaffolds and anticarcinogenic drugs. The rod-shaped and pure aragonite particles of30±5 nm in diameter were reproducibly synthesized when micron-sized cockle shells powders were mechanically stirred for 90 min at room temperature in presence of a nontoxic and nonhazardous biomineralization catalyst, dodecyl dimethyl betaine (BS-12). The findings were verified using a combination of analytical techniques such as variable pressure scanning electron microscopy (VPSEM), transmission electron microscopy (TEM), Fourier transmission infrared spectroscopy (FT-IR), X-ray diffraction spectroscopy (XRD), and energy dispersive X-ray analyser (EDX). The reproducibility and low cost of the method suggested that it could be used in industry for the large scale synthesis of aragonite nanoparticles from cockle shells, a low cost and easily available natural resource.
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Lee, Seon Yong, Uijin Jo, Bongsu Chang, and Young Jae Lee. "Effects of Preferential Incorporation of Carboxylic Acids on the Crystal Growth and Physicochemical Properties of Aragonite." Crystals 10, no. 11 (October 22, 2020): 960. http://dx.doi.org/10.3390/cryst10110960.
Full textAbstract:
The preferential incorporation of carboxylic acids into aragonite and its effects on the crystal growth and physicochemical properties of aragonite were systematically investigated using a seeded co-precipitation system with different carboxylic acids (citric, malic, acetic, glutamic, and phthalic). Aragonite synthesized in the presence of citric and malic acids showed a remarkable decrease in the crystallinity and size of crystallite, and the retardation of crystal growth distinctively changed the crystal morphology. The contents of citric acid and malic acid in the aragonite samples were 0.65 wt % and 0.19 wt %, respectively, revealing that the changes in the physicochemical properties of aragonite were due to the preferential incorporation of such carboxylic acids. Speciation modeling further confirmed that citric acid with three carboxyl groups dominantly existed as a metal–ligand, (Ca–citrate)−, which could have a strong affinity toward the partially positively charged surface of aragonite. This indicates why citric acid was most favorably incorporated among other carboxylic acids. Our results demonstrate that the number of carboxyl functional groups strongly affects the preferential incorporation of carboxylic acids into aragonite; however, it could be suppressed by the presence of other functional groups or the structural complexity of organic molecules.
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Chen, Bin, Xiang He Peng, and Xin Yan Wu. "Lambdoidal Layup of Aragonite Sheets in Conch Shell." Key Engineering Materials 336-338 (April 2007): 2532–35. http://dx.doi.org/10.4028/www.scientific.net/kem.336-338.2532.
Full textAbstract:
The SEM observation on a conch’s shell shows that the shell is a kind of laminated bioceramic composite composed of aragonite layers and organic matrix. Each aragonite layer is parallel with the surface of the shell and consists of many thin aragonite sheets. These aragonite sheets are perpendicular to the layer where they are located. The observation also shows that the orientations of the sheets in different layers are different and these aragonite sheets compose various layups. A kind of lambdoidal layup is found. The maximum pullout force of the lambdoidal layup is analyzed based on its representative model. The result shows that the lambdoidal layup can markedly increase the pullout force of the layup and improve the fracture toughness of the shell.
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Yamamoto, A., M. Kawamiya, A. Ishida, Y. Yamanaka, and S. Watanabe. "Impact of rapid sea-ice reduction in the Arctic Ocean on the rate of ocean acidification." Biogeosciences Discussions 8, no. 5 (October 28, 2011): 10617–44. http://dx.doi.org/10.5194/bgd-8-10617-2011.
Full textAbstract:
Abstract. The largest pH decline and widespread undersaturation with respect to aragonite in this century due to uptake of anthropogenic carbon dioxide in the Arctic Ocean have been projected. The reductions in pH and aragonite saturation state have been caused primarily by an increase in the concentration of atmospheric carbon dioxide. However, in a previous study, simulations with and without warming showed that these reductions in the Arctic Ocean also advances due to the melting of sea ice caused by global warming. Therefore, future projections of pH and aragonite saturation in the Arctic Ocean will be affected by how rapidly the reduction in sea ice occurs. In this study, the impact of sea-ice reduction rate on projected pH and aragonite saturation state in the Arctic surface waters was investigated. Reductions in pH and aragonite saturation were calculated from the outputs of two versions of an earth system model (ESM) with different sea-ice reduction rates under similar CO2 emission scenarios. The newer model version projects that Arctic summer ice-free condition will be achieved by the year 2040, and the older version predicts ice-free condition by 2090. The Arctic surface water was projected to be undersaturated with respect to aragonite in the annual mean when atmospheric CO2 concentration reached 480 (550) ppm in year 2040 (2048) in new (old) version. At an atmospheric CO2 concentration of 520 ppm, the maximum differences in pH and aragonite saturation state between the two versions were 0.08 and 0.15, respectively. The analysis showed that the decreases in pH and aragonite saturation state due to rapid sea-ice reduction were caused by increases in both CO2 uptake and freshwater input. Thus, the reductions in pH and aragonite saturation state in the Arctic surface waters are significantly affected by the difference in future projections for sea-ice reduction rate. The critical CO2 concentration, at which the Arctic surface waters become undersaturated with respect to aragonite on annual mean bias, would be lower by 70 ppm in the version with the rapid sea-ice reduction.
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Liu, Zhen Fa, Mei Fang Yan, Li Hui Zhang, and Hai Hua Li. "Study on the Effect of Magesium Ion on the Crystal Phase of Calcium Carbonate." Advanced Materials Research 554-556 (July 2012): 35–38. http://dx.doi.org/10.4028/www.scientific.net/amr.554-556.35.
Full textAbstract:
Morphology and crystal phase of calcium carbonate, which formed with the presence of Mg2+, were characterized by SEM and XRD. The effect of Mg2+ on crystallization and crystal phase of calcium carbonate was studied. The results showed that the crystal phase of calcium carbonate were mainly calcite and aragonite and the content of aragonite was higher after adding Mg2+ to the blank solution. With the increase of Mg2+ concentration, the content of aragonite increased. The calcium carbonate crystals grain became more fine and the content of aragonite was higher by synergistic treatment between Mg2+ and magnetic field. There was a strong inhibitory effect on calcite when the concentration of Mg2+ was more than 0.50mmol.L-1. The calcite could be transformed into aragonite in the presence of Mg2+ in solution.
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Cho, Kyoung A., Insil Choi, and Il Won Kim. "Ball Milling to Build the Hybrid Mesocrystals of Ibuprofen and Aragonite." Journal of Nanomaterials 2015 (2015): 1–9. http://dx.doi.org/10.1155/2015/163190.
Full textAbstract:
Mesocrystal formation is one of the new paradigms of the nonclassical crystallization, where the assembly of crystal domains is observed. Also, it has been recently employed in studies on drug formulation to utilize controlled dissolution of the drug domains. In this report, ibuprofen was attempted to form hybrid mesocrystals with calcium carbonate crystals. Two polymorphs of calcium carbonate (aragonite and calcite) were used during the solid-state process of ball milling. Structural analyses confirmed the mesocrystal formation of ibuprofen with aragonite but not with calcite. The origin of the observed behavior was found from the higher affinity of ibuprofen to aragonite, especially its (0 1 0) surface, compared to calcite. The hybrid mesocrystals of ibuprofen and aragonite showed the environment-responsive release behavior, where the stability of aragonite was the controlling factor for the release kinetics of ibuprofen.
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Dauphin, Yannicke, Jean-Pierre Cuif, Hiram Castillo-Michel, Corinne Chevallard, Bastien Farre, and Anders Meibom. "Unusual Micrometric Calcite–Aragonite Interface in the Abalone Shell Haliotis (Mollusca, Gastropoda)." Microscopy and Microanalysis 20, no. 1 (November 5, 2013): 276–84. http://dx.doi.org/10.1017/s1431927613013718.
Full textAbstract:
AbstractSpecies of Haliotis (abalone) show high variety in structure and mineralogy of the shell. One of the European species (Haliotis tuberculata) in particular has an unusual shell structure in which calcite and aragonite coexist at a microscale with small patches of aragonite embedded in larger calcitic zones. A detailed examination of the boundary between calcite and aragonite using analytical microscopies shows that the organic contents of calcite and aragonite differ. Moreover, changes in the chemical composition of the two minerals seem to be gradual and define a micrometric zone of transition between the two main layers. A similar transition zone has been observed between the layers in more classical and regularly structured mollusk shells. The imbrication of microscopic patches of aragonite within a calcitic zone suggests the occurrence of very fast physiological changes in these taxa.
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Cuif, Jean-Pierre, Cedrik Lo, and Yannicke Dauphin. "Evidence of a Scheduled End for Prism Growth in the Shell of Pinctada margaritifera: Closure of the Calcite Biomineralization Area by a Specific Organic Membrane." Minerals 14, no. 1 (December 24, 2023): 20. http://dx.doi.org/10.3390/min14010020.
Full textAbstract:
The shell of the pearl oyster Pinctada margaritifera is made up of two layers: an outer layer of calcite prisms and an inner layer of aragonite tablets. Recent studies have shown that the calcite layer develops in a series of steps. We found that the end of prism growth and the start of aragonite deposition are also complex processes. Contrary to the common belief that prism growth is interrupted by the expansion of the aragonite layer, we found that a specific membrane covers the calcite surface before aragonite deposition starts. The earliest aragonite depositions occur as granular spots located only on the surfaces covered by this organic membrane This membrane appears to be the final stage of the calcite biomineralization cycle. This new understanding of calcite development has implications for shell biomineralization research and the production of pearls.
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Yamamoto, A., M. Kawamiya, A. Ishida, Y. Yamanaka, and S. Watanabe. "Impact of rapid sea-ice reduction in the Arctic Ocean on the rate of ocean acidification." Biogeosciences 9, no. 6 (June 29, 2012): 2365–75. http://dx.doi.org/10.5194/bg-9-2365-2012.
Full textAbstract:
Abstract. The largest pH decline and widespread undersaturation with respect to aragonite in this century due to uptake of anthropogenic carbon dioxide in the Arctic Ocean have been projected. The reductions in pH and aragonite saturation state in the Arctic Ocean have been caused by the melting of sea ice as well as by an increase in the concentration of atmospheric carbon dioxide. Therefore, future projections of pH and aragonite saturation in the Arctic Ocean will be affected by how rapidly the reduction in sea ice occurs. The observed recent Arctic sea-ice loss has been more rapid than projected by many of the climate models that contributed to the Intergovernmental Panel on Climate Change Fourth Assessment Report. In this study, the impact of sea-ice reduction rate on projected pH and aragonite saturation state in the Arctic surface waters was investigated. Reductions in pH and aragonite saturation were calculated from the outputs of two versions of an Earth system model with different sea-ice reduction rates under similar CO2 emission scenarios. The newer model version projects that Arctic summer ice-free condition will be achieved by the year 2040, and the older version predicts ice-free condition by 2090. The Arctic surface water was projected to be undersaturated with respect to aragonite in the annual mean when atmospheric CO2 concentration reaches 513 (606) ppm in year 2046 (2056) in new (old) version. At an atmospheric CO2 concentration of 520 ppm, the maximum differences in pH and aragonite saturation state between the two versions were 0.1 and 0.21 respectively. The analysis showed that the decreases in pH and aragonite saturation state due to rapid sea-ice reduction were caused by increases in both CO2 uptake and freshwater input. Thus, the reductions in pH and aragonite saturation state in the Arctic surface waters are significantly affected by the difference in future projections for sea-ice reduction rate. Our results suggest that the future reductions in pH and aragonite saturation state could be significantly faster than previously projected if the sea-ice reduction in the Arctic Ocean keeps its present pace.