Aragonite from Mulanshan Glaucophane Schist: Implications for Regional Evolution of Southwestern Dabie Mountains, Central China

The aragonite, an index mineral of glaucophane schist facies, has not been confirmed in the Dabie Mountains high pressure and ultrahigh pressure metamorphic belts. The Mulanshan glaucophane schist in Huangpi County, Hubei Province is located in the southwestern Dabie Mountains, Central China. The micron sized intergranular aragonite is confirmed with optical microscope (OM) and electron probe microanalysis (EPMA) in the glaucophane schist. The submicrometer sized ellipse aragonite inclusion is observed by using bright field image (BFI), X ray energy damage spectrograph (EDS) and selected area electron diffraction (SAED) with transmission electron microscope in the quartz lens of glaucophane albite epidote chlorite schist from Mulanshan. The presence of aragonite indicates not only the average geothermal gradient of the Mulanshan glaucophane schist less than 10 ℃/km, which is very close to that of eclogite in the Dabie Mountains metamorphic belts, but also the relatively higher concentration of CO2 during the metamorphic process. In addition, the glaucophane schist free of such index minerals as lawsonite, prehnite and pumpellyite, has been attributed to the effect of CO2 on the stability of calcium aluminum silicate minerals during the low grade metamorphism. EDS and SAED analysis results show that the host of aragonite inclusion is amorphous SiO2. The occurrence of amorphous SiO2 indicates a quick cooling process during the exhumation of the Mulanshan glaucophane schist. These results suggest that the rapid exhumation mechanism of the glaucophane schist, the same as that of eclogite in the Dabie Mountains metamorphic belts, occurred in the geodynamic context of subduction obduction.

Enrichment of lanthanides in aragonite

Using the constant addition technique,the coprecipitation of lanthanum,gadolinium,and lutetium with aragonite in seawater was experimentally investigated at 25 ℃.Their concentrations in aragonite overgrowths were determined by inductive coupled plasma mass spectrometer.All these lanthanides were strongly enriched in aragonite overgrowths.The amount of lanthanum,gadolinium,and lutetium incorporated into aragonite accounted for 57%–99%,50%–89%,and 40%–91% of their initial total amount,respectively.With the in...

EFFECT OF ANTHROPOGENIC CO_2 ON THE pH AND THE SATURATION STATES OF CALCITE AND ARAGONITE OF SEAWATER

Growth of phytoplankton, zooplankton and probably most other marine organisms as well, is likely to be affected by the pH of seawater. Growth of calcareous shells and skeletons is less likely to be affect ed by the saturation states of calcite and aragonite but the dissolution is. The increase of CO2 in the oceans due to burning of fossil fuel and clearing of forests is decreasing the pH of seawater and the degress of saturation for calcite and aragonite worldwide. This paper presents the results of the first attempt to estimate the vertical distribution of anthropogenic CO2, and the decreases in pH and the degrees of saturation of calcite and aragonite in seawater near Taiwan. Most ef fects are very small except for the possible dissolution of aragonite on the upper continental slope starting around 2050 AD.

Phase Transformation of Amorphous Calcium Carbonate to Single-Crystalline Aragonite with Macroscopic Layered Structure in the Presence of Egg White Protein and Zinc Ion

Highly oriented calcium carbonate lamellas are exquisite structure produced by biomineralization. Strategies mimicking nature have been developed to synthesize inorganic materials with excellent structures and optimal properties. In our strategy, egg white protein and zinc ion were employed in the solution to induce the crystallization of calcium carbonate, resulting in the macroscopic aragonite laminate with an average length of 1.5 mm, which was comprised of single-crystalline tablets. During the crystallization at initial stage, it was found that the particles displayed the characteristics of amorphous calcium carbonate, which was then transformed into the sophisticated structured aragonite through a multistage assembly process. The rebuilt nacre structure in vitro was achieved owing to the synergistic effects of egg white protein and zinc ion.

¹³C-¹⁸O Bonds in Precipitated Calcite and Aragonite: An <i>ab Initio</i>Study

The 13C-18O bonds in carbonates are potential single-phase geo-thermometers. However, their theoretical distributions (noted as Δ47s) in CO2 degassed from calcite and aragonite with phosphoric acid are unclear. Thus, the isotope reactions of 13C-18O bonds on the growing surfaces of calcite (0001) and aragonite (001) planes were investigated using ab initio techniques. It was found that these reactions determined 13C-18O clumped isotope signatures in bulk calcite and aragonite minerals with novel Δ47 polynomials: and for temperatures ranging from 260 to 1500 K. These theoretical results were in good agreement with the experimental data. In addition, the influence of phosphoric acid on these polynomials was at the level of 0.01‰.

Comparing the regeneration potential between PLLA/Aragonite and PLLA/ Vaterite pearl composite scaffolds in rabbit radius segmental bone defects

Mussel-derived nacre and pearl,which are natural composites composed CaCO3 platelets and interplatelet organic matrix,have recently gained interest due to their osteogenic potential.The crystal form of CaCO3 could be either aragonite or vaterite depending on the characteristics of mineralization template within pearls.So far,little attention has been paid on the different osteogenic capacities between aragonite and vaterite pearl.In the current work,aragonite or vaterite pearl powders were incorporated into poly-L-lactic acid(PLLA)scaffold as bio-functional fillers for enhanced osteogenesis.In intro results revealed that PLLA/aragonite scaffold possessed stronger stimulatory effect on SaOS-2 cell proliferation and differentiation,evidenced by the enhanced cell viability,alkaline phosphatase activity,collagen synthesis and gene expressions of osteogenic markers including osteocalcin,osteopotin and bone sialoprotein.The bone regeneration potential of various scaffolds was evaluated in vivo employing a rabbit critical-sized radial bone defect model.The X-ray and micro-CT results showed that significant bone regeneration and bridging were achieved in defects implanted with composite scaffolds,while less bone formation and non-bridging were found for pure PLLA group.Histological evaluation using Masson's trichrome and hematoxylin/eosin(H&E)staining indicated a typical endochondral bone formation process conducted at defect sites treated with composite scaffolds.Through three-point bending test,the limbs implanted with PLLA/aragonite scaffold were found to bear significantly higher bending load compared to other two groups.Together,it is suggested that aragonite pearl has superior osteogenic capacity over vaterite pearl and PLLA/aragonite scaffold can be employed as a potential bone graft for bone regeneration.

Spatial variability of summertime aragonite saturation states and its influencing factor in the Bering Sea

The Bering sea is susceptible to ocean acidification driven by both human activities(anthropogenic CO_(2))and distinctive natural processes.To assess the situation of ocean acidification,we investigated the spatial variability of aragonite saturation states(ΩAr)in July 2010 during the 4th Chinese National Arctic Research Expedition(CHINARE).The surface waters were all oversaturated with respect to aragonite(ΩAr>1)due to high biological removal,andΩAr ranged from 1.43 to 3.17.The relatively lowΩAr values were found in the western Bering Strait and eastern nearshore region of the Bering Sea Shelf,which were associated with the upwelling and riverine input,respectively.In the subsurface,theΩAr decreased to generally low saturation states and were observed to be strongly undersaturated(ΩAr<1)in the bottom waters with a lowest value of 0.45,which might be caused by remineralization.However,unlike prior studies,the lowΩAr values in the shallow nearshore region were still above the saturation horizon throughout the water column,which were probably counteracted by high local primary production.In the context of climate change and increasing anthropogenic CO_(2)absorption,the suppression and undersaturation ofΩAr in the Bering Sea are not only attributed to the natural processes but also the accumulation of anthropogenic CO_(2).

A biomimetic experimental study of magnesium ion mineralization in Mg-enriched aragonite

In this work, we test the hypothesis that the Mg2+content in biogenic aragonite has a systematic relationship with biomolecules. A series of biomimetic experiments were conducted to show the dependence of Mg2+in aragonite on the model organic molecules added to the mineralizing solution, including the concentration of various organics, mineralization temperature, Mg/Ca ratio and Mg2+initial concentration. The mineralized products were characterized by powder X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), field emission scanning electron microscopy(FESEM), thermogravimetric analysis(TGA), and inductively coupled plasma-atomic emission spectrometry(ICP-AES). High Mg2+is detected in aragonite obtained in the presence of organics, whereas the lowest Mg2+is measured in aragonite without organics. Moreover, the concentration of Mg2+in aragonite increases gradually with the amended organics. Mg K-edge NEXAFS spectra show that the magnesium microenvironment in aragonite is similar to the organic-associated environment, indicating that the Mg2+ions are not on the aragonite lattices, but adhere to the intracrystalline organics. Furthermore, the mineralization temperature, Mg/Ca ratio and Mg2+content in mineralization medium significantly influence Mg2+content in aragonite, reiterating the effect of the microenvironment on aragonite biomineralization.

Three-dimensional biofabrication of an aragoniteenriched self-hardening bone graft substitute and assessment of its osteogenicity in vitro and in vivo

A self-hardening three-dimensional(3D)-porous composite bone graft consisting of 65 wt%hydroxyapatite(HA)and 35 wt%aragonite was fabricated using a 3D-Bioplotter®.New tetracalcium phosphate and dicalcium phosphate anhydrous/aragonite/gelatine paste formulae were developed to overcome the phase separation of the liquid and solid components.The mechanical properties,porosity,height and width stability of the end products were optimised through a systematic analysis of the fabrication processing parameters including printing pressure,printing speed and distance between strands.The resulting 3D-printed bone graft was confirmed to be a mixture of HA and aragonite by X-ray diffraction,Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy.The compression strength of HA/aragonite was between 0.56 and 2.49 MPa.Cytotoxicity was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)assay in vitro.The osteogenicity of HA/aragonite was evaluated in vitro by alkaline phosphatase assay using human umbilical cord matrix mesenchymal stem cells,and in vivo by juxtapositional implantation between the tibia and the anterior tibialis muscle in rats.The results showed that the scaffold was not toxic and supported osteogenic differentiation in vitro.HA/aragonite stimulated new bone formation that bridged host bone and intramuscular implants in vivo.We conclude that HA/aragonite is a biodegradable and conductive bone formation biomaterial that stimulates bone regeneration.Since this material is formed near 37°C,it will have great potential for incorporating bioactive molecules to suit personalised application;however,further study of its biodegradation and osteogenic capacity is warranted.The study was approved by the Animal Ethical Committee at Tongji Medical School,Huazhong University of Science and Technology(IACUC No.738)on October 1,2017.

Carbon and Oxygen Isotopic Composition of Surface-Sediment Carbonate in Bosten Lake (Xinjiang,China) and its Controlling Factors

Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition （δ^13C） values of the carbonate sediment （-1‰ to -2‰） have no relation to the oxygen isotope composition of the carbonate （δ^18O） values （-7‰ to -8‰）, with both isotopes showing a low variability. The carbonate content is low （〈20%）. Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ^13C values between approximately ＋0.5‰ and ＋3‰, and δ^18O values between -1‰ and -5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg-calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg-calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.

The Micro/Nanostructure Characteristics and the Mechanical Properties of Hemifusus tuba Conch Shell

The mollusk shell mobilizes calcium from environment for skeletal mineralization.This occurs through synthesizing solidsin solution in the presence of organic molecules of specific interior regions of the conch shell.The ultrastructure and microhardnessof the Hemifusus tuba conch shell living in the Huang/Bo sea area are investigated in the paper.It is shown that thecomposition and microstructure of the mollusk shell vary in different positions.The prodissoconch shell consists only of aragonitewith the crossed-lamellar microstructure.While the spiral shell and the body shell of the Hemifusus tuba conch shell arecomposed of one calcite layer and several aragonite layers.The calcite layer consists of cylindrical grains,but the aragonitelayers are crossed-lamellar ultrastructure at three size scales.The minimum structure size (the third-order lamella) is at about20 nm - 80 nm.The margin of shell aperture is only composed of calcite with cylindrical grains.This natural optimization of theshell microstructure is intimately due to the growth of the Organic matrix.At different positions the microhardness of molluscshell is different due to different crystal structures and crystal arrangements.The growth process of shells allows a constantrenewal of the material,thus enabling their functional adaptation to external environments.

Biogenic carbonate formation and sedimentation in the Xisha Islands: evidences from living Halimeda

A recent island survey reveals that the Xuande Atoll and the Yongle Atoll in the Xisha Islands can be classified into one of two systems：the depleted atoll system and growth atoll system;the survey also indicates that the decreased area of several shoals is an unbearable burden for the Xisha Islands, of which the largest island area is 2.13 km2 and the minimum elevation is 1.4 m. According to a survey on the ecological characteristics of Halimeda in the Laolongtou breaker zone of Shidao Island in the Xisha Islands, the green and white living Halimeda are collected, the isotopic ages of 14C contained in the Halimeda are shown to be 27 years and 55 years, respectively, and carbonate mainly occurs in five types, i.e., luster, segment, sand, sand grain, and marl in the formation. The Halimeda segments mainly provide the carbonate sediments of long-term biogenic deposits in the reef environment and the annual productivity per area is 60–100 g/m2;the characteristics of the microstructure of the Halimeda are analyzed, the aragonite raphide carbonate is deposited and enriched in the cortexes, medullas and cysts, and the Halimeda generally contain major elements such as C, O, Ca, Cl, Mg, K, Na, S and Al, and are rich in trace elements such as tellurium （Te）, rhodium （Rh） and strontium. It is believed that the Halimeda grow slowly, including the biotic community of reef corals in the reef areas, thus they possess an environmental remediation capacity, but it takes much time to remedy the environment, and it is necessary to make the law to protect the diversity and vulnerability of the Xisha marine ecology, the ecology of the reef community and the island environment in a scientific way. As indicated in the survey, under the background of global warming and sea-level rise, the discovery of large amounts of Halimeda in the Laolongtou sea area is significant for the natural increase of the depleted atoll system of the Xuande Atoll, while the Halimeda segments represent the primary form of the fossil Halimeda, of which the species can be identified and preserved in great numbers under geological conditions. The Miocene was discovered in large amounts in the Xichen-1 well, therefore the study on the characteristics and mechanism of Halimeda carbonate sediments plays a pivotal role in the formation and construction of organic reefs in the South China Sea as well as oil and gas exploration.

Mechanical properties and structure of Haliotis discus hannai Ino and Hemifusus tuba conch shells:a comparative study

Haliotis discus hannai Ino （abalone shell） and Hemifusus tuba conch shell have been studied for the purpose to comparatively investigate the mechanisms by which nature designs composites. It is shown that both shells are composed of aragonite and a small amount of proteins while the conch shell shows finer microstructure but lower strength than aba- lone shell. It is also shown that the fresh shells exhibits better property than those after heat-treatments. It is therefore sup- posed that the size of inorganic substance is not a dominant factor to improve strength, while both proteins in shells and the microstructure of inorganic matter also play important roles.

Ce(Ⅲ) Salt Induced Changes of Superficial Microstructure in Freshwater Pearls

The transition of the superficial microstmcture of freshwater pearls induced by Ce was investigated by means of scanning electron microscopy. The pearls were cultured in freshwater containing 0 （control group ）, 0.5, 1, and 1.5 mg·L^-1 of a Ce additive. X-ray photoelectron spectroscopy （XPS） measurement showed that the concentration of Ce absorbed in the superficial microstmcture of pearls was positively correlated to the additive Ce. At the same time, the surface microstmcture of pearls changed greatly with Ce concentration, the shape of the blocks changed from spindly to perfect regular hexagonal sheets and finally to round discs. The glossiness of the pearls changed correspondingly with the microstmcture, pearls possessing the regular hexagonal blocks having the highest glossiness. Therefore, the REE Ce exerted a significant influence on the microstructure and glossiness of freshwater pearls. An appropriate quantity of Ce may improve the glossiness of pearls.

Effects of Copper-Zinc Alloy Doped with Rare Earth Elements on Crystal of Calcium Carbonate

A copper-zinc alloy doped with rare earth elements was prepared and the mechanism was demonstrated in a simulating boiler and circulating cooling water with rigidity 1 mmol·L-1. The polar curve and scale inhibiting ability of the alloy was tested by a corrosion measurement system and a scale inhibition evaluation system, respectively. Scale samples were characterized with SEM and XRD. It is found that the transfer of cations could be promoted by doping with proper rare earth elements, and the corrosion potentials descend by 25～126 mV. The results indicated that the copper-zinc alloy doped with rare earth elements has higher scale inhibiting ability of CaCO3. The growth of calcite was affected by zinc ions dissolved because of primary battery reaction, and the transition of calcium carbonate from aragonite to calcite was hampered resulting in the proportion of aragonite to calcite is changed from 1.7∶1 to 2.7∶1.

A Modified Integrated Model of the Internal Structure of Chinese Cultured Pearls

Optical and micro-infrared microscope were used to observe the internal structure and mineral composition of high and low quality Chinese seawater and freshwater cultured pearls.Results clearly reveal that aragonite and calcite are found in seawater cultured pearls,but vaterite is not found.In contrast,vaterite and aragonite are found in freshwater cultured pearls,but calcite is not found.Based on our analysis and observations of the internal structure of high and low quality cultured pearls,a modified integrated model of the internal structure of Chinese cultured pearls was established.Our revisions to the previous model focus on significant differences within the prismatic layer of Chinese cultured pearls.

Simulation of global ocean acidification and chemical habitats of shallow-and cold-water coral reefs

Using the UVic Earth System Model, this study simulated the change of seawater chemistry and analyzed the chemical habitat surrounding shallow- and cold-water coral reefs from the year 1800 to 2300 employing RCP2.6, RCP4.5, RCP6.0, and RCP8.5 scenarios. The model results showed that the global ocean will continue to absorb atmospheric CO2. Global mean surface ocean temperature will rise 1.1-2.8 K at the end of the 21st century across RCP scenarios. Meanwhile, the global mean surface ocean pH will drop 0.14--0.42 and the ocean surface mean con- centration of carbonate will decrease 20%--51% across the RCP scenarios. The saturated state of sea water with respect to calcite carbonate minerals （t2） will decrease rapidly. During the pre-industrial period, 99% of the shallow-water coral reefs were surrounded by seawater with t2 〉 3.5 and 87% of the deep-sea coral reefs were surrounded by seawater with aragonite supersaturation. Within the 21st century, except for the high mitigation scenario of RCP2.6, almost none shallow-water coral reefs will be surrounded by seawater with g2 〉 3.5. Under the intensive emission scenario of RCP8.5, by the year 2100, the aragonite saturation horizon will rise to 308 m under the sea surface from 1138 m at the pre- industrial period, thus 73% of the cold-water coral reefs will be surrounded by seawater with aragonite undersaturation. By the year 2300, only 5% of the cold-water coral reefs will be surrounded by seawater with aragonite supersaturation.

Contribution to the Study of Hot Water Scaling Phenomenon in the South of Touristic Area in Agadir City

This work aims to study the phenomenon of scaling observed in the hot water pipelines in the southern seaside touristic installations of Agadir city. This phenomenon has led to the formation of solid deposits and adherents to the internal walls of the facilities of the hot water. This deposit is at the origin of several technical, economic and environmental problems. It causes a decrease in the lifetime of boilers and a reduction of thermal exchanges and consequently a decrease in the energy efficiency of heating systems. In the present study, the samples of scale have been carried out at different points of hot water pipelines. The characterization of different scale samples recovered was conducted by X-ray fluorescence (XRF), elemental analysis (CHNS-O), infrared spectrometry (IR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Analytical results showed that scale samples collected on different sites in touristic hot water system are mostly formed by calcium carbonate. Thermodynamic conditions in the site were favourable to the aragonite variety formation.

Control of Crystal Size and Morphology of Calcium Carbonate Crystal Polymorphism

Calcium carbonate, the main component of lime, has been widely used in industry due to its stability and economy. Calcium carbonate has three types of crystalline polymorphism, calcite, aragonite and vaterite, each with different properties. Therefore, the control of crystal polymorphism is required for industrial applications. In addition, the control of crystal size and shape is similarly required for different applications. In this study, the effect of SrCO3 on the size control of fine aragonite-type calcium carbonate crystals by uniform urea precipitation and the effect of SrCO3 addition was investigated by adding solid strontium carbonate and dissolved strontium carbonate. The addition of solid strontium carbonate affected the crystal polymorphism and size of the calcium carbonate produced, depending on the properties of the solid particles and the amount of SrCO3 added. Experiments on the addition of dissolved SrCO3 showed that the supersaturation formation rate could be controlled to control the crystal polymorphism.

Undue Hardness/Modulus Ratio Claims instead of Physical Penetration Resistance and Applications with Mollusk Shells

The Nanoindentation is a precise technique for the elucidation of mechanical properties. But such elucidation requires physically based interpretation of the loading curves that is widely still not practiced. The use of indentation hardness H and indentation modulus Er is unphysical and cannot detect the most important phase-transitions under load that very often occur. The claim that H versus E plots relate linearly for all different materials is neither empirically found nor correctly deduced. It is most dangerous by producing incorrect materials properties and misleading. The use of H/E (that is also called “elasticity index”) in complicated formulas for brittle parameter, yield strength, toughness, and so-called “true hardness” is also in error. The use of H/E cannot reveal the true qualities of materials without considering phase-transitions under load that require the correct exponent 3/2 on h for the loading curves (instead of disproved 2). This is exemplified with the physical data of different mollusk shells that experience phase-transitions, a new bionics model, and different contributions for their strengthening. The data are compared to the ones of aragonite and calcite and vaterite.