Coordination of Sr and Mg in calcite and aragonite

Finch, Adrian A.; Allison, Nicola

doi:10.1180/minmag.2007.071.5.539

Cited by 123 publications

(96 citation statements)

References 22 publications

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“…The amount of Sr (apfu) in the sample from Spain is about three times more than that from Italy (Table 1). Other studies have also shown that Sr is important in aragonite (Caspi et al 2005, Finch & Allison 2007.…”

Section: Linear Structural Trendsmentioning

confidence: 98%

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THE ORTHORHOMBIC STRUCTURE OF CaCO3, SrCO3, PbCO3 AND BaCO3: LINEAR STRUCTURAL TRENDS

Antao

Hassan

2009

The Canadian Mineralogist

153

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The crystal structures of four isostructural orthorhombic carbonates, CaCO 3 (aragonite), SrCO 3 (strontianite), PbCO 3 (cerussite), and BaCO 3 (witherite), were obtained by Rietveld refinements using data acquired by synchrotron high-resolution powder X-ray diffraction (HRPXRD). For BaCO 3 , powder neutron-diffraction data were obtained and refined by the Rietveld method. For aragonite, we also carried out a refinement of the structure by single-crystal X-ray diffraction. These carbonates belong to the space group Pmcn, with Z = 4. The CO 3 group is slightly non-planar, and the two independent C-O distances are slightly different. The CO 3 group becomes more symmetrical and less aplanar from CaCO 3 to BaCO 3 (M 2+ radii : Ca < Sr < Pb < Ba). The CaCO 3 structure is, therefore, the most distorted, whereas the BaCO 3 structure is the least distorted. Several linear structural trends are observed in plots of selected parameters as a function of the unit-cell volume, V. These parameters are radii of the nine-coordinated M 2+ cations, the unit-cell axes, the average and distances, average angle, and aplanarity. These linear trends are the result of the effective size of the divalent ionic radius of the M cations that are coordinated to nine oxygen atoms. The geometrical features of the CO 3 group can be obtained reliably only by using neutron-diffraction data, especially in the presence of other heavy atoms.Keywords: CaCO 3 , aragonite, SrCO 3 , strontianite, PbCO 3 , cerussite, BaCO 3 , witherite, Rietveld refinements, synchrotron highresolution powder X-ray diffraction (HRPXRD), neutron diffraction, crystal structure. SOMMAIreNous avons affiné la structure cristalline de quatre carbonates orthorhombiques isostructuraux, CaCO 3 (aragonite), SrCO 3 (strontianite), PbCO 3 (cérusite), et BaCO 3 (witherite), par la méthode de Rietveld en utilisant les données acquises par diffraction X à haute résolution avec rayonnement synchrotron. Pour le BaCO 3 , nous avons utilisé des données obtenues par diffraction neutronique, aussi affinées par la méthode de Rietveld. Pour l'aragonite, nous avons affiné la structure par diffraction X sur monocristal. Ces carbonates répondent au groupe spatial Pmcn, avec Z = 4. Le groupe CO 3 est légèrement non planaire, et les deux distances C-O indépendantes diffèrent légèrement. Le groupe CO 3 devient plus symétrique et moins aplanaire en allant de CaCO 3 à BaCO 3 (M 2+ rayon : Ca < Sr < Pb < Ba). La structure de CaCO 3 serait donc la plus difforme, tandis que la structure de BaCO 3 serait la moins difforme. Plusieurs tendances structurales sont évidentes dans les tracés de paramètres choisis en fonction du volume de la maille élémentaire, V. Parmi ces paramètres sont le rayon des cations M 2+ à coordinence neuf, les dimensions le long des axes de la maille élémentaire, les distances et moyennes, l'angle moyen, et l'aplanarité. Ces tracés linéaires sont le résultat de la dimension effective du rayon ionique du cation M bivalent coordonné aux ne...

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Section: Linear Structural Trendsmentioning

confidence: 98%

“…Finch & Allison (2007) used X-ray absorption fine structure (XAFS) to show that Sr substitutes for Ca in aragonite and causes a small (2%) dilation, whereas Sr substitution for Ca in calcite causes a 6.5% dilation.…”

Section: Linear Structural Trendsmentioning

confidence: 99%

THE ORTHORHOMBIC STRUCTURE OF CaCO3, SrCO3, PbCO3 AND BaCO3: LINEAR STRUCTURAL TRENDS

Antao

Hassan

2009

The Canadian Mineralogist

153

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“…40),41) Another possible origin is the difference in coordination number: 42) Mg 2+ ion is characterized by six-fold coordination while Ca 2+ ion is considered to be nine-fold in aragonite. Although the crystalline phase in SiV completely transformed to calcite within 12 h [ Fig.…”

Section: Yamada Et Al: Preparation Of Siloxane-containing Vaterite Dmentioning

confidence: 99%

Preparation of siloxane-containing vaterite doped with magnesium

Yamada

Ota²,

Nakamura

et al. 2014

J. Ceram. Soc. Japan

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Siloxane-containing vaterite doped with magnesium (MgSiV) was prepared by a carbonation process for application in bone regeneration. Ca(OH) 2 , aminopropyltriethoxysilane (APTES) and Mg(OH) 2 were mixed with a solvent consisting of methanol and distilled water under CO 2 gas. After the mixture was aged, the translucent precursor gel was dried, resulting in the formation of MgSiV particles containing 2.0 wt % magnesium and 2.8 wt % silicon. The MgSiV consists of distorted spherical particles with diameters of approximately 1.3¯m and a thickness of approximately 0.6¯m while the siloxane-containing vaterite without magnesium (SiV) was spherical with a diameter of approximately 1.5¯m. X-ray diffraction (XRD) analysis suggests the incorporation of magnesium into the vaterite structure. Fourier transform infrared spectroscopy (FTIR) indicated the presence of amorphous calcium carbonate (ACC) while the magnesium and the siloxane formed SiOMg bonds. After heating the MgSiV at 500°C, the magnesium removed from the vaterite structure formed SiOMg bonds with the siloxane. The MgSiV released Ca 2+ , Mg 2+ and Si 4+ ions into a Tris buffer solution. The amount of Ca 2+ ion dissolved in the Tris buffer solution increased within the initial 12 h and subsequently decreased with time because of the formation of precipitates.

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“…Various forms of X-ray absorption spectroscopy (XAS), including Near Edge X-ray Absorption Fine Structure (NEXAF-S/XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, have been applied to investigate element coordination in bulk biomineral samples [6][7][8][9] . The development of synchrotron Xray microscope instrumentation, providing nano-scale monochromatic X-ray probes, has added spatial discretion to these techniques, allowing the simultaneous nanoscale mapping and spectroscopy of specific elements within a structure [10][11][12][13] .…”

Section: Synchrotron X-ray Microscopy Of Foraminiferamentioning

confidence: 99%

Synchrotron X-ray microscopy of marine calcifiers: how plankton record past climate change

Redfern

Branson

Read

2017

J. Phys.: Conf. Ser.

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Abstract. We have used STXM and PEEM to reveal the underpinning chemistry and nanoscale structure behind palaeo-climate geochemical signatures, such as trace Mg in shells-proposed proxies for palaeo-ocean temperature. This has allowed us to test the chemical assumptions and mechanisms underpinning the use of such empirical proxies. We have determined the control on driving chemical variations in biogenic carbonates using STXM at the absorption edge of Mg, B, and Na in the shells of modern plankton. The power of these observations lies in their ability to link changes in chemistry, microstructure, and growth process in biogenic carbonate to environmental influences. We have seen that such changes occur at length scales of tens of nanometres and demonstrated that STXM provides an invaluable route to understanding chemical environment and key heterogeneity at the appropriate length scale. This new understanding provides new routes for future measurements of past climate variation in the sea floor fossil record.

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Coordination of Sr and Mg in calcite and aragonite

Cited by 123 publications

References 22 publications

THE ORTHORHOMBIC STRUCTURE OF CaCO3, SrCO3, PbCO3 AND BaCO3: LINEAR STRUCTURAL TRENDS

THE ORTHORHOMBIC STRUCTURE OF CaCO3, SrCO3, PbCO3 AND BaCO3: LINEAR STRUCTURAL TRENDS

Preparation of siloxane-containing vaterite doped with magnesium

Synchrotron X-ray microscopy of marine calcifiers: how plankton record past climate change

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