Search results for "Agoni"

Molluscan Shell Proteins: Primary Structure, Origin, and Evolution

2007

In the last few years, the field of molluscan biomineralization has known a tremendous mutation, regarding fundamental concepts on biomineralization regulation as well as regarding the methods of investigation. The most recent advances deal more particularly with the structure of shell biominerals at nanoscale and the identification of an increasing number of shell matrix protein components. Although the matrix is quantitatively a minor constituent in the shell of mollusks (less than 5% w/w), it is, however, the major component that controls different aspects of the shell formation processes: synthesis of transient amorphous minerals and evolution to crystalline phases, choice of the calciu…

Accurate trace element analysis of speleothems and biogenic calcium carbonates by LA-ICP-MS

2012

The high spatial resolution of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) microanalysis of speleothems and biogenic calcium carbonates makes it possible to improve our understanding of past climatic conditions. However, there are analytical problems associated with this method, such as molecular interferences, elemental fractionation, and mass-load-dependent matrix effects, when using NIST silicate reference glasses for calibration. Our study with a sector-field ICP-MS shows that many masses are affected by interferences, such as 24Mg+ by 48Ca++ or 31P+ by 15N16O+. Elemental fractionation and mass-load-dependent matrix effects have been detected for both 213 and…

Molluscan shell proteins

2004

Abstract The shell secreted by molluscs is one of the most remarkable examples of a matrix-mediated mineralisation performed outside living tissues. The calcifying matrix is a mixture of proteins, glycoproteins, and polysaccharides that precisely self-assemble and control the CaCO 3 polymorph (calcite, aragonite), the size, the shapes of the crystallites, and finally, the texture of the shell. In spite of several biochemical studies, the molecular aspects of the shell building are far from being understood. The present article makes an overview of the most recent molecular data on the proteinaceous components of the shell matrix. These data put into question the classical models of mollusca…

Structural Behavior of Natural Silicate–Carbonate Spurrite Mineral, Ca5(SiO4)2(CO3), under High-Pressure, High-Temperature Conditions

2017

We report on high-pressure and high-temperature angle-dispersive synchrotron X-ray diffraction and high-pressure Raman data up to 27 GPa and 700 K for natural silicate carbonate Ca5(SiO4)2(CO3) spurrite mineral. No phase transition was found in the studied P–T range. The room-temperature bulk modulus of spurrite using Ne as the pressure-transmitting medium is B0 = 77(1) GPa with a first-pressure derivative of B0′ = 5.9(2). The structure compression is highly anisotropic, the b axis being approximately 30% more compressible than the a and c axes. The volumetric thermal expansivity value around 8 GPa was estimated to be 4.1(3) × 10–5 K–1. A comparison with intimately related minerals CaCO3 ca…

Clumped isotope analysis of carbonates: comparison of two different acid digestion techniques

2013

RATIONALE The kinetic nature of the phosphoric acid digestion reaction enables clumped isotope analysis of carbonates using gas source isotope ratio mass spectrometry (IRMS). In most laboratories acid digestions are performed at 25°C in sealed vessels or at 90°C in a common acid bath. Here we show that different Δ47 results are obtained depending on the digestion technique employed. METHODS Several replicates of a biogenic aragonite and NBS 19 were reacted with 104% H3PO4 in sealed vessels at 25°C and at 90°C using a common acid bath. The sample size varied between 4 mg and 14 mg. Purification methods that are standard for clumped isotope analyses were applied to the evolved CO2 before meas…

Clumped isotope thermometry of carbonate-bearing apatite: Revised sample pre-treatment, acid digestion, and temperature calibration

2016

Abstract It has recently been shown that the clumped isotopic composition (Δ47) of carbonate-bearing hydroxyapatite (CHAP) from teeth and bones reveals important information about the body temperature of vertebrates (Eagle et al., 2010, 2011). In this study we reinvestigate the temperature dependence of Δ47 in CHAP, extending the temperature range from 2 to 59 °C. In addition, the effects of chemical pre-treatment of CHAP on its bulk and clumped isotopic composition are studied. CHAP is best reacted with phosphoric acid at 90 to 110 °C minimizing the potential of evolved CO2 or reaction intermediates to re-equilibrate with traces of water in the acid environment. Reaction at 110 °C ensures …

Transition from marine to hypersaline conditions in the Messinian Tripoli Formation from the marginal areas of the central Sicilian Basin

2001

Abstract Three sections of the early Messinian Tripoli Formation from the northern and southern margins of the central Sicilian Basin (Serra Pirciata, Torrente Vaccarizzo, and Marianopoli) have been studied with the aim to reconstruct the sedimentary and environmental changes which occurred during the transition between marine conditions and the evaporitic events of the Salinity Crisis recorded in the overlying Calcare di Base Formation. A detailed biostratigraphic and cyclostratigraphic study provided the opportunity of cycle-by-cycle correlations between the marginal sections and the reference section of Falconara. The main paleoenvironmental changes are recorded by: (1) the evolution of …

Partial high-pressure aragonitization of micritic limestones in an accretionary complex, Tavşanlı Zone, NW Turkey

2006

Pelagic micritic limestones within an upper Cretaceous accretionary complex in the Tavsanli Zone, NW Turkey, preserve textures indicating incomplete prograde transformation of micritic calcite to aragonite, representing the only known example of this type. Aragonitization starts at the central parts of the micritic limestone beds and advances towards the lower and upper parts of the layers at the expense of micrite. Micrite is very fine grained (<0.003 mm) and contains radiolaria, foraminifera and thin shell fragments. Aragonite forms large crystals, up to 3 cm across, with straight grain boundaries and c-axis mostly subparallel to the carbonate beds. Relict micritic portions are devoid of …

Investigation of manganese in salt- and freshwater pearls

2001

Abstract The trace element distribution in natural and cultured pearls is analysed by micro-PIXE, cathodoluminescence (CL) microscopy and spectroscopy and electron spin resonance (ESR) spectroscopy to develop a new method to distinguish cultured from natural pearls. These different kinds of pearls can be identified by their manganese content and its distribution in aragonite and calcite structure, respectively. Manganese content of natural freshwater pearls from Persian Gulf was compared to that of natural freshwater pearls from the Mississippi river (USA). Moreover manganese content of tissue-graft freshwater pearls from Chansu (China) was compared to that of natural freshwater pearls from…

2018

Synthetic materials based on calcium phosphate (CaP) are frequently used as bone graft substitutes when natural bone grafts are not available or not suitable. Chemical similarity to bone guarantees the biocompatibility of synthetic CaP materials, whereas macroporosity enables their integration into the natural bone tissue. To restore optimum mechanical performance after the grafting procedure, gradual resorption of CaP implants and simultaneous replacement by natural bone is desirable. Mg and Sr ions released from implants support osteointegration by stimulating bone formation. Furthermore, Sr ions counteract osteoporotic bone loss and reduce the probability of related fractures. The presen…