Search results for "CALCITE"
showing 10 items of 191 documents
Early homogenous amorphous precursor stages of calcium carbonate and subsequent crystal growth in levitated droplets.
2008
An in situ study of the contact-free crystallization of calcium carbonate in acoustic levitated droplets is reported. The levitated droplet technique allows an in situ monitoring of the crystallization while avoiding any foreign phase boundaries that may influence the precipitation process by heterogeneous nucleation. The diffusion-controlled precipitation of CaCO3 at neutral pH starts in the initial step with the homogeneous formation of a stable, nanosized liquid-like amorphous calcium carbonate phase that undergoes in a subsequent step a solution-assisted transformation to calcite. Cryogenic scanning electron microscopy studies indicate that precipitation is not induced at the solution/a…
Three-dimensional hydration layer mapping on the (10.4) surface of calcite using amplitude modulation atomic force microscopy
2014
Calcite, the most stable modification of calcium carbonate, is a major mineral in nature. It is, therefore, highly relevant in a broad range of fields such as biomineralization, sea water desalination and oil production. Knowledge of the surface structure and reactivity of the most stable cleavage plane, calcite (10.4), is pivotal for understanding the role of calcite in these diverse areas. Given the fact that most biological processes and technical applications take place in an aqueous environment, perhaps the most basic - yet decisive - question addresses the interaction of water molecules with the calcite (10.4) surface. In this work, amplitude modulation atomic force microscopy is used…
Clear signature of the (2 x 1) reconstruction of calcite (1014).
2010
Calcite is a mineral of fundamental importance that plays a crucial role in many fields of research such as biomineralization, biomolecule adsorption, and reactivity as well as industrial and daily life applications. Consequently, the most stable cleavage plane of calcite has been studied extensively using both direct imaging techniques such as atomic force microscopy as well as spectroscopic and diffraction techniques. Several surface structures have been reported for the (10 (1) over bar4) cleavage plane of calcite differing from the simple bulk-truncated structure and an ongoing controversy exists in literature whether the cleavage plane exhibits a (2 x 1) reconstruction or not. We study…
Rapid transformation of inorganic to organic and plant-available phosphorous in soils of a glacier forefield
2012
Abstract Chemical weathering of rocks or sediments is extremely important for the generation of soils, for the evolution of landscape, and as a main source of inorganic nutrients for plant growth and therefore for life. Temporal trends in weathering mechanisms, plant succession and nutrients availability in cold environments can be successfully studied in soil chronosequences along a glacier forefield. In the present paper, this was carried out in the pro-glacial area of Morteratsch. Different forms of phosphorous in the soil, stream and spring water chemistry were investigated. Apatite constitutes the main source of P, but it occurs only as a minor accessory mineral phase in the granitic/g…
HIGH-RESOLUTION MG/CA RATIOS IN A CORALLINE RED ALGA AS A PROXY FOR BERING SEA TEMPERATURE VARIATIONS FROM 1902 TO 1967
2009
We present the first continuous, high-resolution record of Mg/Ca variations within an encrusting coralline red alga, Clathromorphum nereostratum, from Amchitka Island, Aleutian Islands. Mg/Ca ratios of individual growth increments were analyzed by measuring a singlepoint, electron-microprobe transect, yielding a resolution of ~15 samples/year and a 65-year record (1902–1967) of variations. Results show that Mg/Ca ratios in the high-Mg calcite algal framework display pronounced annual cyclicity and archive late spring–late fall sea-surface temperatures (SST) corresponding to the main season of algal growth. Mg/Ca values correlate well to local SST, as well as to an air temperature record fro…
Characterization of major discontinuities from borehole cores of the black consolidated marl formation of Draix (French Alps)
2012
A quantitative description of rock discontinuities present in subsurface cores that were drilled (down to 20 m) in the marls of the Laval and Moulin catchments near Draix (France) is presented. Three kinds of discontinuities are studied: those fully open, those open but filled with clay rich material and those sealed with calcite. With a laser profiler, the topography of facing sides of typical discontinuities was measured with a normal resolution of 1 µm. The probability distribution of the elevation of each surface are obtained and shown to be normal. Possible self-affine scaling invariance of the topography were explored. The mineralogical content of an interface between the marl bulk an…
Detection and origin of different types of annual laminae in recent stalagmites from Zoolithencave, southern Germany: Evaluation of the potential for…
2016
Abstract. An arrangement of three stalagmites from Zoolithencave (southern Germany) was analysed for different types of annual laminae using both microscopic and geochemical methods. The speleothems show visible laminae (consisting of a clear and a brownish, pigmented layer pair) as well as fluorescent and elemental laminae. The age of the speleothems was constrained to 1800 to 1970 AD by 14C-dating of a charcoal piece below the speleothems, detection of the 14C bomb peak, as well as counting of annual laminae. Dating by the 230Th/U-method was impossible due to detrital contamination. On the annual time-scale, the variability of Mg, Ba, and Sr is controlled by Prior Calcite Precipitation (P…
A new simple approach to evaluate pedogenic clay transformation in a Vertic Calcisol
2006
The aim of this study is to characterize the pedogenic clay minerals by using simple approach: Mixing mineralogical and geochemical findings. The fine clay fractions (< 0.1 μm) of a Vertic Cambisol profile were studied by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity (CEC). Qualitative and quantitative mineralogical compositions of the clay mixture were determined. Moreover, chemical equilibria and thermodynamic stabilities of minerals (calcite, gypsum, kaolinite, smectites and illites) were studied using results of ionic activities obtained from total concentration of various aqueous species in water extracts from soil-saturated pastes. XRD ana…
Zirconium and hafnium fractionation and distribution of Rare Earth Elements in neutral–alkaline waters: Case study of Lake Van hydrothermal system, T…
2021
International audience; We investigated the distribution of Zr, Hf, and rare earth elements (REE) as the sum of lanthanides plus Y in the hydrothermal system in the Lake Van area of south-eastern Turkey. This system is characterised by water with variable pH in alkaline conditions resulting from hydrothermal CO2 upraise and neoformation of calcite minerals in near equilibrium with the interacting waters. Zr, Hf, and REE determinations were carried out for aqueous phases and suspended solids in lake water and surrounding thermal springs. We found that dissolved Hf is partitioned relative to Zr during calcite formation and that such fractionation is a function of the Ca2+ activity in warm wat…
The sponge silicatein-interacting protein silintaphin-2 blocks calcite formation of calcareous sponge spicules at the vaterite stage
2013
Ca-carbonate, the inorganic matrix of the spicules from the calcareous sponges, is formed as the result of an enzyme-catalyzed reaction with the carbonic anhydrase [CA] as a decisive component. The growth and the morphology of the spicules are genetically controlled, and are taxon-specific. In the present study it is shown that the silicatein-interacting protein silintaphin-2 is present at the surface of the siliceous spicules of the demosponge Suberites domuncula and prevents the association of calcareous crystals synthesized in vitro to these skeletal elements. Silintaphin-2 comprises a Ca2+-binding domain that is formed by a 22 amino acid-long peptide, N-DDDSQGEIQSDMAEEEDDDNVD-C. This ve…