Zeitschriftenartikel: „Macles de la calcite“

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Lacombe, O., J. Angelier, F. Bergerat und P. Laurent. „Tectoniques superposees et perturbations de contrainte dans la zone transformante Rhin-Saone; apport de l'analyse des failles et des macles de la calcite“. Bulletin de la Société Géologique de France VI, Nr. 5 (01.09.1990): 853–63. http://dx.doi.org/10.2113/gssgfbull.vi.5.853.

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Özgün Çakmak, Ender, Emrah Erdoğan, Cengiz Köksal, Mesut Şişmanoğlu und Uğur Fındıkçıoğlu. „Psoas muscle area index as a predictor of major adverse cardiovascular and limb events in patients with infrarenal aortic occlusions“. Turkish Journal of Vascular Surgery 30, Nr. 2 (19.03.2021): 133–40. http://dx.doi.org/10.9739/tjvs.2021.980.

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Objectives: In this study, we aimed to investigate whether the total psoas muscle area index (TPAI) was a predictive factor of major adverse cardiovascular and limb events (MACLEs) in patients with infrarenal aortic occlusion (IAO). Patients and methods: Between January 2011 and December 2019, a total of 72 patients with IAO (56 males, 16 females; mean age: 58.8±7.0 years; range, 46 to 75 years) were retrospectively reviewed. The TPAI was measured by dividing total psoas muscle area to squared patient height. The primary outcome measure was MACLEs. To estimate the effect of TPAI and clinical factors on prognosis, hazard ratios (HRs) with 95% confidence intervals (CIs) were used. Results: The median follow-up was 32 months (interquartile range 15.9-44). The patients were divided into two groups as MACLE-positive (n=30, 41.6%) and MACLE-negative (n=42, 58.4%). The mean TPAI for MACLE-negative and MACLE-positive patients was 615±171 mm2/m2 and 521±129 mm2/m2, respectively (p=0.036). The presence of increased TPAI values was associated with the decreased MACLE rate (HR: 0.19; 95% CI: 0.09-0.42; p=0.008). Conclusion: Our study results indicate that the TPAI measured by computed tomography scans is an independent prognostic factor for MACLEs in patients with chronic IAO.

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El-Mofty, S. E., und A. A. El-Midany. „Calcite–oleate–oxalate interaction in calcite flotation system“. Particulate Science and Technology 35, Nr. 6 (10.06.2016): 699–703. http://dx.doi.org/10.1080/02726351.2016.1194349.

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Vo-Thanh, D., und Diep-The-Hung. „Theoretical study of the elastic constants of calcite at the transition calcite I-calcite II“. Physics of the Earth and Planetary Interiors 39, Nr. 1 (Juni 1985): 62–71. http://dx.doi.org/10.1016/0031-9201(85)90115-3.

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Mihajlovic, Slavica, Zivko Sekulic, Dusica Vucinic, Vladimir Jovanovic und Bozo Kolonja. „PVC mixtures’ mechanical properties with the addition of modified calcite as filler“. Chemical Industry 66, Nr. 5 (2012): 787–94. http://dx.doi.org/10.2298/hemind111115025m.

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In this study mechanical properties of PVC mixtures (PVC, stabilizer, lubricant, filler) such as tensile strength, tensile elongation, breaking strength, and breaking elongation were investigated. Unmodified calcite, as well as calcite modified by stearic acid, were used as fillers in wet and dry processes. The PVC mixtures containing the calcite modified by wet procedure have better mechanical properties compared to those with the calcite modified by the dry process. Tensile and breaking strength of the PVC mixture containing the calcite modified with 1.5% stearic acid using wet process, are higher for 2.8% and 5.2%, respectively, compared to the PVC mixture containing the calcite modified with the same amount of acid used in the dry process. The tensile strength difference between the mixtures increases with the increase of the concentration of used stearic acid up to 3%. The strength of PVC mixture with the calcite modified by wet process is 3.1% higher compared to the mixture containing calcite modified by dry process. The results showed that the bonding strength between calcite and the adsorbed organic component affected tensile strength, tensile elongation and breaking strength of the PVC mixtures. The best filler was obtained by wet modification using 1.5% stearic acid solution that provided the formation of a stearate monolayer chemisorbed on calcite. The PVC mixtures containing the calcite modified by wet process using 1.5% stearic acid solution exhibited the best mechanical properties. This calcite was completely hydrophobic with dominant chemically adsorbed surfactant, which means that stearate chemisorbed on calcite provided stronger interaction in the calcite-stearic acid-PVC system.

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Alutu, O. E., und M. O. Ihimekpen. „Utilization of Calcite and Calcite-Cement in the Stabilization of Laterites for Low-Cost Hollow Blocks“. Advanced Materials Research 18-19 (Juni 2007): 27–34. http://dx.doi.org/10.4028/www.scientific.net/amr.18-19.27.

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This paper examines the production of calcite and calcite-cement stabilized laterite hollow blocks as low-cost masonry units. First, is the production of laterite hollow blocks solely stabilized with finely ground limestone or calcite followed by the production of laterite hollow blocks stabilized with calcite-cement composite. Laterite was sourced from three locations: Asoro, Evbuotubu and Ugbowo. Blocks were produced using a specially constructed machine with percentages of calcite and calcite-cement content varying from 4% to 16% respectively at compactive pressures of 10.32 and 13.75N/mm2. Equal amounts of calcite and cement are used in the composite. The blocks were then tested for 7, 14 and 28 days strengths after curing. The results show that laterite blocks stabilized with calcite alone do not satisfy the Nigerian Industrial Standards or British Standards for blocks but those stabilized with 8% calcite-cement content, i.e., 4% calcite with 4% cement do, at moulding pressure of 13.7 N/mm2. Based on the local cost data, the results also show that calcite-cement stabilized laterite hollow blocks are 17% cheaper than an equivalent cement-stabilized hollow block and 46% cheaper than the low quality sandcrete blocks sold in the market.

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Saito, Ayaka, Hiroyuki Kagi, Shiho Marugata, Kazuki Komatsu, Daisuke Enomoto, Koji Maruyama und Jun Kawano. „Incorporation of Incompatible Strontium and Barium Ions into Calcite (CaCO3) through Amorphous Calcium Carbonate“. Minerals 10, Nr. 3 (17.03.2020): 270. http://dx.doi.org/10.3390/min10030270.

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Calcite is a ubiquitous mineral in nature. Heavy alkaline-earth elements with large ionic radii such as Sr2+ and Ba2+ are highly incompatible to calcite. Our previous study clarified that incompatible Sr2+ ions can be structurally incorporated into calcite through crystallization from amorphous calcium carbonate (ACC). In this study, we synthesized Sr-doped calcite with Sr/(Sr + Ca) up to 30.7 ± 0.6 mol% and Ba-doped calcite with Ba/(Ba + Ca) up to 68.6 ± 1.8 mol%. The obtained Ba-doped calcite samples with Ba concentration higher than Ca can be interpreted as Ca-containing barium carbonates with the calcite structure which have not existed so far because barium carbonate takes the aragonite structure. X-ray diffraction (XRD) patterns of the Sr-doped and Ba-doped calcite samples obtained at room temperature showed that reflection 113 gradually weakened with increasing Sr/(Sr + Ca) or Ba/(Ba + Ca) ratios. The reflection 113 disappeared at Ba/(Ba + Ca) higher than 26.8 ± 1.6 mol%. Extinction of reflection 113 was reported for pure calcite at temperatures higher than 1240 K, which was attributed to the rotational (dynamic) disorder of CO32− in calcite. Our Molecular Dynamics (MD) simulation on Ba-doped calcite clarified that the CO32− ions in Ba-doped calcites are in the static disorder at room temperature. The CO32− ions are notable tilted and displaced from the equilibrium position of pure calcite.

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HALFORD, BETHANY. „CALCITE CLOSE-UP“. Chemical & Engineering News 87, Nr. 48 (30.11.2009): 7. http://dx.doi.org/10.1021/cen-v087n048.p007.

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Boels, L., R. M. Wagterveld, M. J. Mayer und G. J. Witkamp. „Seeded calcite sonocrystallization“. Journal of Crystal Growth 312, Nr. 7 (März 2010): 961–66. http://dx.doi.org/10.1016/j.jcrysgro.2010.01.016.

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Eriksson, Susan C. „Only a Calcite?!“ Rocks & Minerals 70, Nr. 4 (August 1995): 217–30. http://dx.doi.org/10.1080/00357529.1995.9926626.

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Arvidson, Rolf S., Cornelius Fischer und Andreas Luttge. „Calcite Dissolution Kinetics“. Aquatic Geochemistry 21, Nr. 5 (23.06.2015): 415–22. http://dx.doi.org/10.1007/s10498-015-9268-9.

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Vdović, Neda. „Electrokinetic behaviour of calcite—the relationship with other calcite properties“. Chemical Geology 177, Nr. 3-4 (Juli 2001): 241–48. http://dx.doi.org/10.1016/s0009-2541(00)00397-1.

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Vanderploeg, Henry A., Brian J. Eadie, James R. Liebig, Stephen J. Tarapchak und Rebecca M. Glover. „Contribution of Calcite to the Particle-Size Spectrum of Lake Michigan Seston and Its Interactions with the Plankton“. Canadian Journal of Fisheries and Aquatic Sciences 44, Nr. 11 (01.11.1987): 1898–914. http://dx.doi.org/10.1139/f87-234.

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We determined the contribution of calcite to the total particle-size spectrum of Lake Michigan seston during different seasons in 1978–83 and 1985, employing a novel Coulter counter method, to examine the intensity and ecological effects of calcite whitings that result from autogenic precipitation of calcite. The whitings were most intense during September, when 12–56% of the total particle volume was calcite. Overall, food web dynamics were more controlling of than controlled by whitings. Year-to-year variation in calcite concentration was probably caused by predation-controlled variation in primary production, which drives calcite precipitation through CO2 uptake. Feeding rate of cladocerans in Lake Michigan is slightly reduced (16%) by calcite, but that of copepods is not. Light extinction is only slightly increased. Coprecipitation and sinking of P with calcite is probably a minor factor in regulating P concentration in the epilimnion of Lake Michigan. Removal of nutrients is enhanced by increased sinking rates caused by inclusion of calcite in fecal pellets and matter. Although all of the effects of calcite on plankton dynamics appear to be subtle in Lake Michigan, large effects can be expected for lakes of greater calcium hardness and eutrophy.

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Liu, Zhongyi, Jie Liu, Yinfei Liao, Zilong Ma und Chenxi Jin. „Study on the Influence of Metal Ions on the Dispersion of Fine Calcium Gangue Minerals“. Molecules 27, Nr. 24 (16.12.2022): 8963. http://dx.doi.org/10.3390/molecules27248963.

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In this study, the calcium gangue material calcite (−10 μm) was used to investigate the effects of different kinds of metal ions and dosages on the dispersion behavior of calcite. The test results showed that the dispersion behavior of calcite was poor under strongly alkaline conditions without the addition of metal ions, and the reason for that was calcite dissolved ions. The degree of influence of different metal ions on calcite dispersion behavior was Fe3+ > Mg2+ > Na+. The three metal ion dosage tests showed that the dispersion behavior of calcite became poorer with the increase of metal ion dosage. This mainly showed that with the increase of Na+ dosage, the trend of the dispersion behavior of calcite was not obvious, but with the increase of Fe3+ and Mg2+ dosage, the trend of calcite dispersion behavior changed more. The dispersion behavior of calcite was devastated by 5 × 10−4 mol/L Fe3+ at pH = 4–12. The different mechanisms of the three metal ions were identified by zeta potential, solution chemistry, and XPS analysis. Na+ only changed the zeta potential value of the calcite surface, which acted as a compressed electric double layer. However, the formation of metal hydroxide species or metal hydroxide surface precipitation due to the adsorption of Fe3+ and Mg2+ on the mineral surface resulted in the change of the dispersion behavior of calcite.

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Worden, Richard H., Glenn T. Morrall, Sean Kelly, Peter Mc Ardle und Dinfa V. Barshep. „A renewed look at calcite cement in marine-deltaic sandstones: the Brent Reservoir, Heather Field, northern North Sea, UK“. Geological Society, London, Special Publications 484, Nr. 1 (18.02.2019): 305–35. http://dx.doi.org/10.1144/sp484-2018-43.

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AbstractWireline and seismic acoustic impedance imaging show that the marine part of the clastic Brent Group reservoir in the Heather Field, northern North Sea, contains much calcite cement in the flank parts of the structure. The non-marine Ness Formation and crest parts of the structure contain negligible calcite cement. This localized calcite cement has led to relatively poor reservoir performance since first oil in 1978, although a new suite of wells has boosted production with plans to keep the field active until 2030. Understanding the origin and distribution of calcite cement would help the development of more realistic reservoir models and boost production rates through optimum well location. We have thus used a suite of techniques, including standard point counting, SEM-EDS mineralogy, BSE microscopy, fluid inclusion thermometry and stable isotope analysis, to develop new and improved models of calcite distribution. Calcite seems to have attributes of both early and late diagenetic cement. A 30–40% intergranular volume in calcite cemented beds seems to support pre-compactional growth but high-temperature fluid inclusions and the presence of primary oil inclusions suggest late growth. Much calcite may have developed early but it seems to have recrystallized, and possibly undergone redistribution, at close to maximum burial or had a late growth event. Calcite cement probably originated as marine-derived micrite, bioclasts or early marine cement but adopted the isotopic characteristics of high-temperature growth as it recrystallized. Quartz grains have corroded outlines in calcite-cemented areas with one sample, with 79% calcite cement, displaying signs of nearly total replacement of quartz grains by calcite. The flank localization of calcite cement remains to be explained, although it could be due to primary depositional factors, early diagenetic loss of calcite from crestal regions or late diagenetic loss of calcite from crestal regions. Controversially, the growth of calcite seems to be associated with quartz dissolution, although the geochemical and petrophysical cause of this remains obscure. Diagenetic loss of quartz from sandstones cannot easily be explained by conventional modelling approaches and yet seems to be an important phenomenon in Heather sandstones.

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MENG, QINGFENG, JOHN HOOKER und JOE CARTWRIGHT. „Role of pressure solution in the formation of bedding-parallel calcite veins in an immature shale (Cretaceous, southern UK)“. Geological Magazine 156, Nr. 5 (15.05.2018): 918–34. http://dx.doi.org/10.1017/s0016756818000377.

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AbstractBedding-parallel fibrous calcite veins in black shales (Cretaceous, southern UK) were investigated using a combined field, stable isotopic geochemistry, petrographic and crystallographic method to examine their formation mechanism. Calcite veins occur in all shale beds and are most abundant in the bituminous shales of the Chief Beef Beds. The calcite fibres in these veins exhibit either an antitaxial fibre growth with curvy stylolites as the median zone, or a predominantly syntaxial, upwards growth. The calcite veins range from –0.49 to 1.78‰ of δ13C values, and –6.53 to –0.03‰ of δ18O values, which are both similar to those of their host shales. Our petrographic observations demonstrate that subhorizontal and interconnecting microstylolite networks commonly occur within the calcite veins. Equant calcite grains in the median zones exhibit indenting, truncating and also interpenetrating grain contacts. It is interpreted that the fibrous calcite veins were sourced by neomorphic calcite from their host shales, with evidence from the δ13C signatures, pressure-solution features (stylolites, microstylolites and grain contact styles) and embedded fossil ghosts within the veins. The diagenetic fluids, from which calcite was precipitated, were a mixing of the original seawaters and 18O-depleted meteoric waters. Development of bedding-parallel calcite veins is considered to have been enhanced by pressure solution as a positive feedback mechanism, which was facilitated by the overburden pressure as the maximum principal stress. Calcite fibres, with a predominant subvertical c-axis orientation, exhibit a displacive growth in porous shales and a replacive growth at vein-limestone contacts. This study highlights the critical role of pressure solution in the formation of bedding-parallel calcite veins during burial and diagenesis of immature black shales.

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Chalmin, Emilie, Yves Perrette, Bernard Fanget und Jean Susini. „Investigation of Organic Matter Entrapped in Synthetic Carbonates—A Multimethod Approach“. Microscopy and Microanalysis 19, Nr. 1 (21.12.2012): 132–44. http://dx.doi.org/10.1017/s1431927612013773.

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AbstractOrganic matter (OM) entrapped in calcite is regularly used for environmental studies; however, insertion mechanisms and types of interaction remain poorly understood. The present study used a new methodology to investigate interactions between OM and the calcite matrix during crystallization processes with humic acid (HA) entrapment. A multimethod approach confirmed that HA is both adsorbed onto the calcite surface and incorporated into the calcite lattice during crystallization. Our results also confirm the log-linear correlation between fluorescence intensity and calcite matrix HA concentration. Fourier transform infrared spectroscopy showed that HA in colloidal conformation is adsorbed onto the calcite surface as a result of the structure of the OH stretching band. We also developed a new method based on synchrotron analysis that uses sulfur as a tracer element for entrapped HA and that localizes the OM electrostatically adsorbed onto the calcite surface. Changes in the sulfur environment, determined using X-ray absorption near-edge structure spectroscopy, indicated more complex insertion mechanisms than simple adsorption of HA during calcite crystallization. Desorption experiments revealed the stability of the OM atomic structure and its layered nature. These results allowed us to draw up a general model of OM insertion in calcite.

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Xing, Dingquan, Ruofan Sun, Shuai Ma, Heping Wen, Zhongchi Wang und Jiushuai Deng. „Effect of Sulfuric Acid Corrosion on Flotation Performance of Calcite by Changing Surface Roughness“. Molecules 29, Nr. 5 (29.02.2024): 1062. http://dx.doi.org/10.3390/molecules29051062.

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Surface roughness is a crucial factor that affects the flotation performance of minerals. In this study, the effect of sulfuric acid corrosion on the surface roughness of calcite flotation was investigated through microflotation tests, scanning electron microscopy (SEM–EDS), atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy, and contact angle analysis. Microflotation test results show that sulfuric acid treatment has a serious negative effect on the floatability of calcite. When the sulfuric acid dosage was 4 mL (3 mol/L), the flotation recovery of calcite was reduced to less than 19%. SEM–EDS and AFM results verified that the sulfuric acid treatment significantly changed the surface morphology of calcite, reduced the average surface roughness and surface area, and reduced the amount of active Ca2+ sites on the calcite surface. As characterized by FT-IR and contact angle analyses, the sulfuric acid treatment enhanced the hydrophilicity of the calcite surface and reduced the amount of sodium oleate adsorbed on the calcite surface. Consequently, sulfuric acid corrosion can reduce the average surface roughness of calcite and have a serious negative effect on the flotation performance of calcite.

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Shahwan, T., B. Zünbül, Ö. Tunusoğlu und A. E. Eroğlu. „AAS, XRPD, SEM/EDS, and FTIR characterization of Zn2+ retention by calcite, calcite–kaolinite, and calcite–clinoptilolite minerals“. Journal of Colloid and Interface Science 286, Nr. 2 (Juni 2005): 471–78. http://dx.doi.org/10.1016/j.jcis.2005.02.047.

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Jones, Brian. „Calcite rafts, peloids, and micrite in cave deposits from Cayman Brae, British West Indies“. Canadian Journal of Earth Sciences 26, Nr. 4 (01.04.1989): 654–64. http://dx.doi.org/10.1139/e89-056.

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Speleothemic deposits from the Oligocene–Miocene Bluff Formation of Cayman Brae include calcite rafts that formed in cave pools. The rafts, which formed at the surface of the cave pools where rapid degassing of CO2 from the surface waters led to the precipitation of the calcite, can be divided into single- or double-sided spar calcite rafts and symmetrical, asymmetrical, or composite micrite – spar calcite rafts. Agitation of the water caused the rafts to sink and accumulate on the floor of the pool.Cavities formed by stacking of the calcite rafts are filled or partly filled with spar calcite, micrite, peloids, and terra rossa glaebules. The micrite laminae, like those in the micrite – spar calcite rafts, probably formed through the merger of peloids, which are formed of either subhedral to euhedral crystals or anhedral to subhedral grains. Available petrographic evidence suggests that the micrite and the peloids formed by precipitation from cave water. This example demonstrates that high-magnesium calcite peloids are not necessarily indicative of early marine diagenesis in reefs.

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Meinhold, Guido, Nick M. W. Roberts, Arzu Arslan, Sören Jensen, Jan Ove R. Ebbestad, Anette E. S. Högström, Magne Høyberget, Heda Agić, Teodoro Palacios und Wendy L. Taylor. „U–Pb dating of calcite in ancient carbonates for age estimates of syn- to post-depositional processes: a case study from the upper Ediacaran strata of Finnmark, Arctic Norway“. Geological Magazine 157, Nr. 8 (10.06.2020): 1367–72. http://dx.doi.org/10.1017/s0016756820000564.

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AbstractResults of in situ U–Pb dating of calcite spherulites, cone-in-cone (CIC) calcite and calcite fibres from a calcareous concretion of the upper Ediacaran of Finnmark, Arctic Norway, are reported. Calcite spherulites from the innermost layers of the concretion yielded a lower intercept age of 563 ± 70 Ma, which, although imprecise, is within uncertainty of the age of sedimentation based on fossil assemblages. Non-deformed CIC calcite from the bottom part of the concretion yielded an age of 475 ± 25 Ma, which is interpreted as the age of CIC calcite formation during a period of fluid overpressure induced during burial of the sediments. Deformed CIC calcite from the top part of the concretion yielded an age of 418 ± 23 Ma, which overlaps with a known Caledonian tectono-metamorphic event, and indicates a potential post-depositional overprint at this time. Calcite fibres that grew in small fissures along spherulite rims, which are interpreted as a recrystallization feature during deformation and formation of a cleavage, gave an imprecise age of 486 ± 161 Ma. Our results show that U–Pb dating of calcite can provide age constraints for ancient carbonates and syn- to post-depositional processes that operated during burial and metamorphic overprinting.

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Mansour, A. M., W. E. Piller und C. L. Lengauer. „Quantitative mineraiogical analyses of carbonate rich sediments by X-ray powder diffraction“. Powder Diffraction 10, Nr. 2 (Juni 1995): 112–16. http://dx.doi.org/10.1017/s0885715600014469.

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The quantitative analysis of carbonate rich materials is tested with conventional and Rietveld methods. In the case of artificial mixtures of aragonite, calcite, Mg-calcite and quartz the Rietveld method provides reliable results with a maximum deviation of ±5 wt %. In the natural samples, however, the conventional methods give more reliable results in comparison to chemical and sedimentological measurements. This is caused by the peak overlap of calcite/Mg-calcite, peak roadening of the Mg-calcite, and the difficulties in the refinement of minor amounts of feldspar phases.

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Kotlyar, V. D. „The Calcite Crystallinity and the Age of Limestone Brick Mortars of Medieval Objects of the North of the Byzantine Oecumene“. Materials Science Forum 974 (Dezember 2019): 83–89. http://dx.doi.org/10.4028/www.scientific.net/msf.974.83.

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The paper describes the process of recrystallization of portlandite of limestone mortar in calcite. The degree of crystallinity of calcite in limestone mortar of some medieval objects of the north of the Byzantine oecumene is shown through the example of Abkhazia and calcite in natural limestone and marble. The work provides a comparative analysis of the calcite crystallinity and the estimated age of the building objects according to historical and architectural data. It is proven that the higher the calcite crystallinity is the elder the lime mortar and, accordingly, the architectural object is.

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Reardon, E. J., und R. Fagan. „The calcite/portlandite phase boundary: enhanced calcite solubility at high pH“. Applied Geochemistry 15, Nr. 3 (März 2000): 327–35. http://dx.doi.org/10.1016/s0883-2927(99)00061-x.

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Qasim, Ahmed, und Hameed Hussein Alwan. „Adsorptive Desulfurization of Iraqi Light Naphtha Using Calcite and Modified Calcite“. Iraqi Journal of Chemical and Petroleum Engineering 25, Nr. 1 (30.03.2024): 83–93. http://dx.doi.org/10.31699/ijcpe.2024.1.8.

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This study used the adsorption method to remove sulfur compounds from light naphtha fuel by using calcite and modified calcite as adsorbents. The calcite was prepared from chicken eggshells by heating and activation methods. It was modified by mixing it with commercial activated carbon as a new adsorbent. XRD and FTIR were used to characterize the adsorbents. Light naphtha fuel from the Al-Diwaniyah refinery, with a sulfur concentration of 776 ppm, was used in batch adsorption studies. Various operation conditions that affect the adsorption process were studied such as temperature (20–40 °C), weight of the adsorbent (1-3 g), and contact time (15–45 min) at constant mixing speed (300 rpm). In this study, the Minitab Program-Box-Behnken design was used to design experiments in batch adsorption studies of light naphtha, which is considered more straightforward and accurate because it shows the effect of each dependent factor on the adsorption efficiency and removal ratio. Results and analysis showed that the increase in temperature, the amount of adsorbent, and contact time would increase the removal efficiency. The analysis of adsorption equilibrium isotherms shows that the experimental data follows the Freundlich isotherm model for adsorbents. According to the results of the study, the highest removal percentages of sulfur content of light naphtha using calcite and modified calcite were 61% and 79%, respectively.

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Wu, Yongxiang, Minyi Huang, Chunlin He, Kaituo Wang, Nguyen Thi Hong Nhung, Siming Lu, Gjergj Dodbiba, Akira Otsuki und Toyohisa Fujita. „The Influence of Air Nanobubbles on Controlling the Synthesis of Calcium Carbonate Crystals“. Materials 15, Nr. 21 (23.10.2022): 7437. http://dx.doi.org/10.3390/ma15217437.

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Numerous approaches have been developed to control the crystalline and morphology of calcium carbonate. In this paper, nanobubbles were studied as a novel aid for the structure transition from vaterite to calcite. The vaterite particles turned into calcite (100%) in deionized water containing nanobubbles generated by high-speed shearing after 4 h, in comparison to a mixture of vaterite (33.6%) and calcite (66.3%) by the reaction in the deionized water in the absence of nanobubbles. The nanobubbles can coagulate with calcite based on the potential energy calculated and confirmed by the extended DLVO (Derjaguin–Landau–Verwey–Overbeek) theory. According to the nanobubble bridging capillary force, nanobubbles were identified as the binder in strengthening the coagulation between calcite and vaterite and accelerated the transformation from vaterite to calcite.

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Ye, Shaoxiong, Pan Feng und Jiaping Liu. „Topographic Analysis of Calcite (104) Cleavage Surface Dissolution in Ethanol–Water Solutions“. Minerals 11, Nr. 4 (02.04.2021): 376. http://dx.doi.org/10.3390/min11040376.

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The interaction of organic molecules with calcite surfaces plays a key role in many geochemical, industrial and biomineralization processes, and exploring the influences of organic molecules on calcite reactions is crucial for a fundamental understanding of the reaction mechanisms. Here, we used digital hologram microscopy to explore the in situ evolution of the calcite (104) surfaces when dissolved in ethanol–water solutions, and total organic carbon analysis was applied to confirm the adsorption of ethanol by calcite. The results showed that the bulk dissolution rate of calcite decreases as the volume fraction of ethanol increases, and the topographic features of etch pits were also altered by the presence of ethanol. When exposed to too much ethanol, the etch pits’ growth was inhibited and their shapes tended to change from rhombuses in ultrapure water to triangles. Our results provide insights into the interaction between adsorbed ethanol and evolving calcite crystal, which highlights the dissolution regulation of calcite by organic molecules that could benefit a broad range of fields.

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Leiss, B., S. Siegesmund und K. Weber. „Texture Asymmetries as Shear Sense Indicators in Naturally Deformed Mono- and Polyphase Carbonate Rocks“. Textures and Microstructures 33, Nr. 1-4 (01.01.1999): 61–74. http://dx.doi.org/10.1155/tsm.33.61.

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The microstructural and quantitative texture analyses of a naturally deformed calcite mylonite, a dolomite mylonite and a dolomitic calcite mylonite reveal different texture asymmetries for comparable deformation conditions. Calcite shows a c-axis maximum rotated against the shear sense with regard to the main shear plane. In contrast, the dolomite shows a c-axis maximum rotated with the shear sense. In accordance with the experimental and simulated textures from the literature, this difference proves e-twinning and r-slip for calcite and f-twinning and c-slip for dolomite as the main deformation mechanisms. The dolomitic calcite mylonite shows for both the calcite and the dolomite a c-axis maximum rotated against the shear sense. On account of the microstructure of this sample, the dolomite texture has been passively overtaken from the deformation texture of calcite during a late-deformative dolomitization. The results significantly contribute to the interpretation that the sampled shear zone is a transpressive strike–slip fault.

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Auqué, Luis F., M. Cinta Osácar, Concha Arenas, Neven Cukrov, Sonja Lojen und Carlos Sancho. „Controls on Mg/Ca Ratios in Recent Stromatolites: Insights from Fluvial Systems in the Iberian Range (Spain)“. Minerals 13, Nr. 1 (29.12.2022): 57. http://dx.doi.org/10.3390/min13010057.

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The utility of the Mg/Ca elemental ratio of calcite ((Mg/Ca)calcite) as a temperature indicator in continental carbonate deposits is a matter of debate due to the different results obtained by diverse authors. In this study, we aimed to test the reliability of the (Mg/Ca)calcite in fluvial carbonates. We selected the recent tufa stromatolite records of four rivers on the Iberian Peninsula for the trace element analysis based on six-monthly sampling. Previous sedimentary and hydrological studies on these fluvial basins provided the information for this work. The water temperature estimates for the stromatolite (Mg/Ca)calcite substantially differed from the measured water temperatures in most of the studied cases. We thus assessed other factors that participate in the control of the Mg partitioning between water and calcite. The correction of the detrital Mg content yielded water temperatures that matched the measured ones in one of the rivers. The (Mg/Ca)water, water discharge and calcite precipitation rates may also occasionally influence the (Mg/Ca)calcite. The six-month behaviour of some of these parameters could interfere with the relationship between the (Mg/Ca)calcite and water temperature. According to these results, and their comparison with other non-marine carbonates, the wide variety of parameters that are involved in the (Mg/Ca)calcite limit it as a geochemical thermometer in continental sedimentary environments.

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Abdel-Halim, Mohamed M., Ruihua Fan, Mohamed A. Abdel Khalek, Renji Zheng, Shihong Xu und Zhiyong Gao. „Apatite–Calcite Flotation Separation Using Sodium N-Lauroylsarcosinate as a Selective Collector“. Minerals 13, Nr. 7 (21.07.2023): 970. http://dx.doi.org/10.3390/min13070970.

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Froth flotation is a commonly utilized beneficiation technique for effectively separating apatite from other gangue minerals, such as calcite. It is difficult to achieve good separation with fatty acid collectors due to their similar interactions with apatite and calcite. In this work, sodium N-lauroyl sarcosinate (SNLS) was used as the collector for the selective separation of calcite from apatite without a depressant. The experiments revealed that SNLS had a much better selectivity and a stronger affinity with calcite compared to apatite, with little effect on the flotation of apatite observed at a pH of 10. Fourier transform infrared (FTIR) analyses were conducted to explain the selective collector process of SNLS. The mechanism experiments demonstrate that SNLS can chemically bond to apatite and calcite minerals to produce Ca-NLS chelates. The active O atoms of the amide and carboxyl groups of SNLS accomplish this. Calcite has a greater Ca-reactivity than apatite, and as a result, the adsorption quantity on the calcite surface is greater than that on the apatite surface. FTIR analyses indicate that SNLS exhibits a greater affinity for the calcite surface than for apatite, a finding that is supported by first-principle density functional theory (DFT) calculations showing a higher adsorption energy of SNLS on the calcite surface. DFT calculations showed that SNLS forms stronger O-Ca bonds on the calcite surface and is less hindered by H2O. This work shows that the surfactant sodium N-lauroylsarcosinate (SNLS) can be an ideal collector for the flotation of phosphate minerals.

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Daniels, C. J., R. M. Sheward und A. J. Poulton. „Biogeochemical implications of comparative growth rates of <i>Emiliania huxleyi</i> and <i>Coccolithus</i> species“. Biogeosciences 11, Nr. 23 (10.12.2014): 6915–25. http://dx.doi.org/10.5194/bg-11-6915-2014.

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Abstract. Coccolithophores, a diverse group of phytoplankton, make important contributions to pelagic calcite production and export, yet the comparative biogeochemical role of species other than the ubiquitous Emiliania huxleyi is poorly understood. The contribution of different coccolithophore species to total calcite production is controlled by inter-species differences in cellular calcite, growth rate and relative abundance within a mixed community. In this study we examined the relative importance of E. huxleyi and two Coccolithus species in terms of daily calcite production. Culture experiments compared growth rates and cellular calcite content of E. huxleyi (Arctic and temperate strains), Coccolithus pelagicus (novel Arctic strain) and Coccolithus braarudii (temperate strain). Despite assumptions that E. huxleyi is a fast-growing species, growth rates between the three species were broadly comparable (0.16–0.85 d−1) under identical temperature and light conditions. Emiliania huxleyi grew only 12% faster on average than C. pelagicus, and 28% faster than C. braarudii. As the cellular calcite content of C. pelagicus and C. braarudii is typically 30–80 times greater than E. huxleyi, comparable growth rates suggest that Coccolithus species have the potential to be major calcite producers in mixed populations. To further explore these results we devised a simplistic model comparing daily calcite production from Coccolithus and E. huxleyi across a realistic range of relative abundances and a wide range of relative growth rates. Using the relative differences in growth rates from our culture studies, we found that C. pelagicus would be a larger source of calcite if abundances of E. huxleyi to C. pelagicus were below 34:1. Relative abundance data collected from North Atlantic field samples (spring and summer 2010) suggest that, with a relative growth rate of 88%, C. pelagicus dominated calcite production at 69% of the sites sampled. With a more extreme difference in growth rates, where C. pelagicus grows at 1/10th of the rate of E. huxleyi, C. pelagicus still dominated calcite production in 14% of the field. These results demonstrate the necessity of considering interactions between inter-species differences in growth rates, cellular calcite and relative abundances when evaluating the contribution of different coccolithophores to pelagic calcite production. In the case of C. pelagicus, we find that there is strong potential for this species to make major contributions to calcite production in the North Atlantic, although estimates of relative growth rates from the field are needed to confirm our conclusions.

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Teng, Jianbin, Longwei Qiu, Cunfei Ma, Huimin Liu, Zhengwei Fang und Jiejie Yu. „Rare Earth Partition Characteristics and Sedimentary Diagenetic Response in Layered Argillaceous Limestone: Taking the Shale of Upper Es4 in the Nx55 Well Area as an Example“. Geofluids 2023 (09.03.2023): 1–15. http://dx.doi.org/10.1155/2023/2248940.

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Taking the layered argillaceous limestone in the upper Es4 in the Dongying Sag as the research object, the geochemical analysis of major, trace, and rare earth elements (REEs) established the response relationship between REE distribution characteristics and sedimentary diagenesis. The average values of total light REE ( Σ LREE )/total heavy REE ( Σ HREE ) of micrite calcite and argillaceous laminae are 6.75 and 4.06, respectively. The LREEs and HREEs are differentiated, consistent with the distribution pattern of REEs in the crust. Th and U elements are more enriched in the sediments in the lacustrine sedimentary environment than in the diagenetic calcite veins. In primary sediments (argillaceous clay and micrite calcite laminae), LREEs are more enriched, HREEs are depleted, and Eu shows positive anomaly-enrichment characteristics. The LREEs and HREEs of the sparry calcite veins are lower than those of the original sediment argillaceous clay and micrite calcite, showing characteristics of a negative anomaly depletion. Sparry calcite veins originate from diagenetic fluid crystallization and precipitation and have the characteristics of low Th and U, evident positive anomalies of Sr and Eu, and substantial depletion of La. The distribution patterns of REEs within the four components of the laminated argillaceous sparry limestone reflect the order of REE distribution from primary sediment laminae (argillaceous clay and micrite calcite) to diagenetic laminae (calcite veins). Compared with the North American shale, the four components of the contact surface between the argillaceous and bright crystalline laminae, the micrite calcite, the calcite veins, and the argillaceous laminae all showed weak negative δ Ce anomalies and positive δ Eu anomalies. The fractionation degree between LREEs and HREEs reflected by La / Sm cn and Gd / Yb cn is in descending order: the interface between the argillaceous lamina and sparry calcite lamina, micritic calcite, calcite vein, and argillaceous lamina. The argillaceous laminar material has the characteristics of basalt REEs, indicating that the terrestrial debris and argillaceous lacustrine shale in the upper Es4 member of the Niuzhuang subsag are primarily derived from the basic extrusive rocks of the Qingtuozi bulge. REE differentiation is most noticeable at the interface between the argillaceous lamina and calcite vein, proving the directionality of REE differentiation from the original sedimentary lamina to the diagenetic lamina. Shale in the study area is primarily deposited below the redox interface of water at a certain depth, and the deposition rate is stable and slow, providing good conditions for preserving organic matter.

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Hagège, S. „Description en coincidence des macles de deformation dans les metaux de structure hexagonale compacte“. Acta Metallurgica 37, Nr. 4 (April 1989): 1199–215. http://dx.doi.org/10.1016/0001-6160(89)90115-6.

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Wei, Zhao, Junhao Fu, Haisheng Han, Wei Sun, Tong Yue, Li Wang und Lei Sun. „A Highly Selective Reagent Scheme for Scheelite Flotation: Polyaspartic Acid and Pb–BHA Complexes“. Minerals 10, Nr. 6 (23.06.2020): 561. http://dx.doi.org/10.3390/min10060561.

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Previous studies have proved that the lead complexes of benzohydroxamic acid (Pb–BHA) are effective collectors of scheelite flotations; however, the separation of scheelite from calcite needs depressants with high selectivity. In this study, we reported a novel depressant for calcite minerals, and Pb–BHA served as the collector of scheelite. The flotation behavior of polyaspartic acid (PASP) in a scheelite and calcite flotation that uses Pb–BHA was determined via flotation experiments. Furthermore, the selective adsorption of PASP on the mineral surfaces and the effect of PASP on the adsorption of Pb–BHA on the mineral surfaces were investigated through zeta potential measurements, X-ray photoelectron spectroscopy (XPS), crystal chemistry calculations, and Fourier transform infrared spectroscopy (FTIR) measurements. Thus, PASP demonstrated high selectivity in both scheelite and calcite and contributed to the successful separation of scheelite from calcite. PASP exhibited a higher adsorption capacity and stronger chemisorption with the active sites of calcium atoms on the calcite surface. The crystal chemistry calculations indicated that the distance of the PASP functional groups matched with the calcium distance of a calcite mineral surface, which can be attributed to the selectivity of PASP. Furthermore, the adsorption of PASP impeded the adsorption of Pb–BHA on the calcite surfaces, whereas the opposite was the case for scheelite. The mutually reinforcing selectivity of PASP and Pb–BHA considerably contributes to the efficient flotation separation of scheelite from calcite.

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Zhang, Zehan, Kelai Xi, Honggang Xin, Chunming Yang, Hui Zhao, Youcheng Wang, Weidong Dan und Bin Luo. „Origin of Calcite Cements in Tight Sandstone Reservoirs of Chang 8 Member of the Yanchang Formation in Zhijing-Ansai Area, Ordos Basin, China“. Energies 15, Nr. 24 (15.12.2022): 9544. http://dx.doi.org/10.3390/en15249544.

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Calcite cement is a common type of cementation in tight sandstone reservoirs of the Upper Triassic Yanchang Formation Chang 8 Member in the Zhijing-Ansai area of the Ordos Basin, which has significant influence on reservoir densification and heterogeneity. Calcite cements affect the quality of the reservoir conspicuously. The characteristics and origins of calcite were investigated using a series of approaches from the perspective of petrography and geochemistry, including thin section observation and identification, cathode luminescence, scanning electron microscopy, AMICS analysis, LA-ICP-MS elements analysis, and carbon and oxygen isotopes analysis. The results of all analytical tests indicated that calcite cements can be divided into two types according to their occurrence and origins. Type-I calcite cements mainly occur in sandstone reservoirs near the sandstone–mudstone interface or the sandstone layers adjacent to mudstone. Generally, there is no chlorite coating around them, and they appear dark orange under cathode luminescence. The carbon source of Type-I calcite cements may be related to the compaction and drainage of mudstone. Type-II calcite cements are formed in the early stage, and their carbon source may be related to the compaction and drainage of the adjacent mudstone. Type-II calcite cements are surrounded by chlorite coating primarily present in the interior of fine-grained sandstone, showing as bright yellow under cathode luminescence. Decarboxylation of organic matter in the source rocks may provide a crucial source of carbon for Type-II calcite cements.

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Antia, A. N., K. Suffrian, L. Holste, M. N. Müller, J. C. Nejstgaard, P. Simonelli, Y. Carotenuto und S. Putzeys. „Dissolution of coccolithophorid calcite by microzooplankton and copepod grazing“. Biogeosciences Discussions 5, Nr. 1 (02.01.2008): 1–23. http://dx.doi.org/10.5194/bgd-5-1-2008.

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Abstract. Independent of the ongoing acidification of surface seawater, the majority of the calcium carbonate produced in the pelagial is dissolved by natural processes above the lysocline. We investigate to what extent grazing and passage of coccolithophorids through the guts of copepods and the food vacuoles of microzooplankton contribute to calcite dissolution. In laboratory experiments where the coccolithophorid Emiliania huxleyi was fed to the rotifer Brachionus plicatilis, the heterotrophic flagellate Oxyrrhis marina and the copepod Acartia tonsa, calcite dissolution rates of 45–55%, 37–53% and 5–22% of ingested calcite were found. We ascribe higher loss rates in microzooplankton food vacuoles as compared to copepod guts to the strongly acidic digestion and the individual packaging of algal cells. In further experiments, specific rates of calcification and calcite dissolution were also measured in natural populations during the PeECE III mesocosm study under differing ambient pCO2 concentrations. Microzooplankton grazing accounted for between 27 and 70% of the dynamic calcite stock being lost per day, with no measurable effect of CO2 treatment. These measured calcite dissolution rates indicate that dissolution of calcite in the guts of microzooplankton and copepods can account for the calcite losses calculated for the global ocean using budget and model estimates.

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Loope, David. „Plant Root Systems Preserved in the Permian Cedar Mesa Sandstone at Moki Dugway, Southeastern Utah“. Geosites 1 (30.12.2019): 1–6. http://dx.doi.org/10.31711/geosites.v1i1.60.

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Rooted green plants represent the base of the food chain for most terrestrial ecosystems, but, compared to animal burrows, root systems are relatively rarely recognized in ancient sedimentary rocks. Plant roots that penetrate unconsolidated sand dunes, especially those containing not only quartz grains, but also abundant grains of calcite (CaCO) are commonly replaced by fine crystals of calcite (Klappa, 1980). These structures (known by geologists as rhizoliths from the Greek for “root rock”) are one form of calcite cemented soil and sediment called caliche. Caliche crystallizes well above the water table and its calcite crystals are tiny because of rapid evaporation of soil water. One source of the calcium (Ca) and carbonate (CO) ions necessary for making the calcite of caliche is falling dust, and another source is the dissolution of calcite grains already in the soil.

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Guo, Ya Ping, Bao Qiang Li, Yu Zhou und De Chang Jia. „Effect of pH Values on Conversion of Calcite Crystals into Calcium Phosphate Phases in Buffer Solutions“. Key Engineering Materials 353-358 (September 2007): 2183–86. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.2183.

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Calcium phosphate phases with laminar-plate structure were converted from calcite powders after soaking in phosphate buffer solutions of pH’s 6.0-8.0 at 37 °C for 9 days. The effect of pH values on the conversion of calcite crystals was investigated by X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectroscopy. If the pH value of a buffer solution is kept at 6.0, calcite powders are converted mainly to dicalcium phosphate dehydrate (DCPD) or octacalcium phosphate (OCP). If the pH value is kept at 6.4 or 7.0, calcite powders are converted mainly to OCP. Hydroxyapatite (HAP) with poorly crystalline can be obtained from calcite powders both by treatment of a basic buffer solution, and by treatment of an acid buffer solution without regulating its pH value during the reaction. The conversion mechanism of calcite crystals is a dissolution-precipitation reaction.

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Шмурак, С. З., В. В. Кедров, А. П. Киселев, Т. Н. Фурсова und И. И. Зверькова. „Влияние индия на спектральные и структурные характеристики Lu-=SUB=-0.98-x-=/SUB=-In-=SUB=-x-=/SUB=-Eu-=SUB=-0.02-=/SUB=-BO-=SUB=-3-=/SUB=-“. Физика твердого тела 62, Nr. 12 (2020): 2110. http://dx.doi.org/10.21883/ftt.2020.12.50215.162.

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The structure and the IR absorption and luminescence spectra of the Lu0.98-хInхEu0.02BO3 orthoborates are studied at 0 ≤ x ≤ 0.1. The Lu1-xInxBO3 solid solution, which consists of lutetium borate LuBO3 having two stable structural modifications (calcite, vaterite) and indium orthoborate InBO3 having one structural modification (calcite), crystallizes at x = 0.1 to form a calcite structure almost throughout the volume. We showed that the structural transformations in the Lu0.98-хInхEu0.02BO3 orthoborates induced by an increase in the In3+ ion concentration begin in the near-surface layers of the orthoborate microcrystals. The amount of calcite increases in the sample volume with x, and calcite occupies 98% of the Lu0.88In0.1Eu0.02BO3 sample volume.

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Mârza, Ioan, Călin Gabriel Tămaș, Romulus Tetean, Alina Andreica, Ioan Denuț und Réka Kovács. „Epithermal Bicolor Black and White Calcite Spheres from Herja Ore Deposit, Baia Mare Neogene Ore District, Romania-Genetic Considerations“. Minerals 9, Nr. 6 (08.06.2019): 352. http://dx.doi.org/10.3390/min9060352.

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White, black, or white and black calcite spheres were discovered during the 20th century within geodes from several Pb-Zn ± Au-Ag epithermal vein deposits from the Baia Mare ore district, Eastern Carpathians, Romania, with the Herja ore deposit being the maiden occurrence. The black or black and white calcite spheres are systematically accompanied by needle-like sulfosalts which are known by the local miners as “plumosite”. The genesis of epithermal spheres composed partly or entirely of black calcite is considered to be related to the deposition of calcite within voids filled by hydrothermal fluids that contain acicular crystals of sulfosalts, mostly jamesonite in suspension. The proposed genetic model involves gravitational concentration of sulfosalt acicular crystals towards the base of open spaces within paleochannels of epithermal fluid flow and the subsequent formation of calcite spheres by geochemical self organization of amorphous calcium carbonate that crystallized to calcite via vaterite.

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Hassan, Kamaleldin. „Note on the stable isotope values of vein calcite in the El-Seboah peralkaline granite (SW Egypt)“. Mineralogia 42, Nr. 2-3 (01.01.2011): 113–20. http://dx.doi.org/10.2478/v10002-011-0010-y.

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Note on the stable isotope values of vein calcite in the El-Seboah peralkaline granite (SW Egypt)Stable isotope data for carbon (δ13C) and oxygen (δ18O) are used to constrain the environments of calcite formation in two veins in the El-Seboah peralkaline granite in south-western Egypt. Vein I with calcite-magnetite-goethite-hematite-quartz, and vein II with calcite-magnetite-goethite-kaolinite-hematite-quartz are texturally distinct. The calcite of each vein has characteristic δ13C- and δ18O-values: + 0.32 and -7.28‰ for vein I and + 1.16 and - 1.21‰ for vein II, respectively. The observed differences between the δ13C values of the two veins indicate that they represent two separate systems of primary dissolved inorganic carbon formed at or near equilibrium with atmospheric CO2. The δ18O values, on the other hand, indicate calcite deposition from meteoric waters which were fresh for vein I and brackish for vein II.

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Zeng, Xiao Le, Shi Qiang Lu, Jian Min Zeng, Zhi Liu Hu und De Guang Cao. „Effect of Calcite Content on Firing Characteristics and its Sintering Properties of Nixing Pottery“. Advanced Materials Research 941-944 (Juni 2014): 560–63. http://dx.doi.org/10.4028/www.scientific.net/amr.941-944.560.

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According to the characteristics that purple red of nixing pottery contains an amount of calcite; different samples were fired with different content of calcite in the mud and varying temperature under oxidizing conditions. The phase composition and microstructure were analyzed. The results show that number and size of pores in the sintered samples increased and pore morphology changed from irregular closed hole to round closed then converted to irregular inter-connected one along with the increase of calcite content. As calcite content in the mud increases the viscosity of liquid phase decreases while the crystalline phase gradually increased as sintering, thus wollastonite phase transformed into eutectic phase of aluminum scapolite and wollastonite, and quartz content gradually reduced. Higher sintering temperatures and content of calcite were helpful to the reduction in viscosity, as calcite content increased gradually, the amount of liquid phase increased at first then decreased.

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Payne, V. E., R. E. M. Rickaby, L. G. Benning und S. Shaw. „Calcite crystal growth orientation: implications for trace metal uptake into coccoliths“. Mineralogical Magazine 72, Nr. 1 (Februar 2008): 269–72. http://dx.doi.org/10.1180/minmag.2008.072.1.269.

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AbstractInorganic calcite precipitation experiments were conducted to determine whether inducing specific orientations of calcite crystal growth can cause the enrichment of cations larger than Ca. Malonic acid (CH2(COOH)), a di-carboxylic acid, was used to poison growth on acute kink sites, promoting growth on obtuse kink sites, causing calcite crystals elongated along their c-axes to form in a mechanism similar to that seeninthe growth of E. huxleyi coccoliths. Calcite was precipitated with a range of malonic acid concentrations (0 to 10-1 M), and 9x10-5 M of either SrCl2 or MgCl2. The results show that calcite crystals precipitated in the presence of large malonic acid concentrations show significant elongation along the c axis, and suggest that increasing malonate concentrations corresponded with increasing DSr. Experiments with 10-1 M malonic acid caused elevated DSr comparable to that predicted for E. huxleyi coccolith calcite (Langer et al., 2006).

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Devda, Sakshi, und Harshada Joshi. „Screening and Characterization of Calcite Solubilizing Bacteria isolated from Marble Slurry dumped in Sukher, Udaipur, Rajasthan, India“. Research Journal of Biotechnology 16, Nr. 11 (25.10.2021): 78–82. http://dx.doi.org/10.25303/1611rjbt7882.

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Rajasthan is known as mineral majestic state as more than 50 types of minerals are produced including marble. Various types of marbles are spread over in 16 belts in 33 districts of the State. Large amount of marble slurry is discharged as a waste generated by the quarries which is dumped in empty pits in the forest area; thereby creating huge dumping area. The present study was undertaken for screening and characterization of calcite solubilizing bacteria from marble slurry collected from dumping yard in Sukher, Udaipur, India. Screening of calcite solubilizing bacteria was done on calcite agar medium. Calcite solubilizing efficiency (CSE) and calcite solubilizing activity index (CSAI) of the isolates were determined using 0.1% calcite agar medium at 37C for 10 days of incubation. Characterization of the isolates was done on the basis of morphological, biochemical and molecular methods. A total of 27 isolates appeared on calcite agar medium after an incubation of 24 hours at 37°C. Among them only 3 isolates namely isolate CS6, CS13 and CS25 showed clear halo zone of 20 mm, 29 mm and 2mm diameters respectively after 10 days of incubation indicating demonstrable calcite solubilizing activity. The maximum CSE and CSAI 362% and 4.62 respectively were observed for isolate CS13. Isolates CS6, CS13 and CS25 were identified as Exiguobacterium aquaticum CS6 (accession no. MK353511), Staphylococcous aureus CS13 (accession no. KY694446) and Bacillus endophyticus CS25 (accession no. MK353513) respectively. Two isolates that showed remarkable calcite solubilizing activity can be further analyzed for their possible use in restoration of marble slurry contaminated soil.

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Suchý, Václav, Kateřina Pachnerová Brabcová, Jiří Zachariáš, Ivo Světlík und Lenka Borecká. „Gothic-Arch Calcite from Speleothems of the Bohemian Karst (Czech Republic): Its Occurrence, Microscopic Ultrastructure and Possible Mechanism of Growth“. Minerals 11, Nr. 8 (11.08.2021): 866. http://dx.doi.org/10.3390/min11080866.

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Gothic arch calcite, a specific crystallographic variety of calcite known from some hot springs and tufa streams, has been newly recognized in the Koněprusy Caves. The gothic-arch calcite occurs on the exteriors of exotic coralloid speleothems where it coexists with scalenohedral (dogtooth) spar crystals. The crystals exhibit microscopic ultrastructural features including deeply eroded topography, etch pits, and spiky and ribbon calcite crystallites, pointing to its extensive natural etching. Many gothic-arch calcites originated as late-stage, secondary overgrowths on older, etched dogtooth calcite crystals. Its characteristic outward curvature resulted from the recrystallization of etching-liberated fine carbonate grains and newly formed needle-fiber calcite laths, which were accumulated and bound on the faces and at the bases of corroded crystals. These intimately coexisting destructive and constructive processes of carbonate crystal corrosion and growth were probably mediated by bacteria, fungi, or other microorganisms. Fluid inclusions embedded in calcite crystals point to a vadose setting and temperatures below ~50 °C. This, combined with the wider geological context, indicates that the gothic arch calcite crystals originated only during the late Pleistocene to Holocene epochs, when the cave, initially eroded by hypogene fluids in the deeper subsurface, was uplifted to the subaerial setting and exposed to the meteoric waters seeping from the topographic surface. The radiocarbon analysis shows that gothic-arch calcite crystals are generally older than ~55,000 years, but the surface layers of some crystals still reveal a weak 14C activity, suggesting that microbiologically mediated alterations of the speleothems may have been occurring locally until now.

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Izumoto, Satoshi, Johan Alexander Huisman, Yuxin Wu und Harry Vereecken. „Effect of solute concentration on the spectral induced polarization response of calcite precipitation“. Geophysical Journal International 220, Nr. 2 (15.11.2019): 1187–96. http://dx.doi.org/10.1093/gji/ggz515.

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SUMMARY Induced calcite precipitation is used in geotechnics to modify the mechanical and hydrological properties of the underground. Laboratory experiments have shown that spectral induced polarization (SIP) measurements can detect calcite precipitation. However, the results of previous studies investigating the SIP response of calcite precipitation were not fully consistent. This study aims to investigate how the SIP response of calcite depends on solute concentration to explain the differences in SIP response observed in previous studies. A four-phase experiment with SIP measurements on a column filled with sand was performed. In phase I, calcite precipitation was generated for a period of 12 d by co-injecting Na2CO3 and CaCl2 solutions through two different ports. This resulted in a well-defined calcite precipitation front, which was associated with an increase in the imaginary part of the conductivity ($\sigma ^{\prime\prime}$). In phase II, diluted solutions were injected into the column. This resulted in a clear decrease in $\sigma ^{\prime\prime}$. In phase III, the injection of the two solutions was stopped while calcite precipitation continued and solute concentrations in the mixing zone decreased. Again, this decreased $\sigma ^{\prime\prime}$. Finally, the injection rate of the Na2CO3 solution was reduced relative to that of the CaCl2 solution in phase IV. This resulted in a shift of the mixing zone away from the calcite precipitation front established in phase I and an associated decrease of $\sigma ^{\prime\prime}$. These results imply that the SIP response of calcite is highly sensitive to the solute concentration near the precipitates, which may explain previously reported conflicting results.

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Dawson, J. B., und R. W. Hinton. „Trace-element content and partitioning in calcite, dolomite and apatite in carbonatite, Phalaborwa, South Africa“. Mineralogical Magazine 67, Nr. 5 (Oktober 2003): 921–30. http://dx.doi.org/10.1180/0026461036750151.

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AbstractA carbonatite sample from Phalaborwa, South Africa, consists of apatite, magnetite and a calcitedolomite ‘perthite’ which is interpreted as being due to exsolution of dolomite from a high-Mg calcite precursor. Carbon and oxygen isotope data indicate that the carbonates are equilibrated. In situ ionmicroprobe analyses for Fe, Mn, Na, Si, Y, the REEs, Pb, Th and U give the following average concentrations (in ppm) in the sequence apatite, calcite, dolomite: Fe 98, 1680, 8190; Mn 61, 510, 615; Na 1171, 627, 125; Si 368; 1.6, 0.2; Sr 4447, 5418, 2393; Ba 37, 2189, 75; La 1245, 300, 67; Y 121, 50, 5.8; Pb 16, 5.4, 1.4; Th 20, 0.02, 0; U 2.4, 0, 0.01. The concentrations are reasonably uniform in both apatite and dolomite, but in calcite are more variable. Na, Si, Y, the REEs, Pb, Th and U partition into apatite relative to both carbonates (and, hence, the precursor carbonate); KD ap/cc for REE decreases from ∽4 for La to ∽2 for Tm. There is almost equal partitioning of Sr between apatite and calcite. During separation of dolomite from calcite, Sr and Ba partition strongly into calcite and all the other analysed elements, except Fe and Mn, also preferentially enter calcite. The REEs prefer calcite relative to dolomite, and the KD dol/cc is reasonably constant, only varying from 0.23 to 0.17. Sr, Ba and Pb in the carbonates, and their partitioning between the calcite and dolomite, differ from other carbonatite carbonates reported in the literature.

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González-Lemos, Saúl, José Guitián, Miguel-Ángel Fuertes, José-Abel Flores und Heather M. Stoll. „Technical note: An empirical method for absolute calibration of coccolith thickness“. Biogeosciences 15, Nr. 4 (22.02.2018): 1079–91. http://dx.doi.org/10.5194/bg-15-1079-2018.

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Abstract. As major calcifiers in the open ocean, coccolithophores play a key role in the marine carbon cycle. Because they may be sensitive to changing CO2 and ocean acidification, there is significant interest in quantifying past and present variations in their cellular calcification by quantifying the thickness of the coccoliths or calcite plates that cover their cells. Polarized light microscopy has emerged as a key tool for quantifying the thickness of these calcite plates, but the reproducibility and accuracy of such determinations has been limited by the absence of suitable calibration materials in the thickness range of coccoliths (0–4 µm). Here, we describe the fabrication of a calcite wedge with a constant slope over this thickness range, and the independent determination of calcite thickness along the wedge profile. We show how the calcite wedge provides more robust calibrations in the 0 to 1.55 µm range than previous approaches using rhabdoliths. We show the particular advantages of the calcite wedge approach for developing equations to relate thickness to the interference colors that arise in calcite in the thickness range between 1.55 and 4 µm. The calcite wedge approach can be applied to develop equations relevant to the particular light spectra and intensity of any polarized light microscope system and could significantly improve inter-laboratory data comparability.

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EENSAAR, JAAN, TÕNU PANI, MIKK GAŠKOV, HOLAR SEPP und KALLE KIRSIMÄE. „Stable isotope composition of hypogenic speleothem calcite in Kalana (Estonia) as a record of microbial methanotrophy and fluid evolution“. Geological Magazine 154, Nr. 1 (11.12.2015): 57–67. http://dx.doi.org/10.1017/s0016756815000928.

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AbstractAeronian (Silurian Period) carbonate rocks in Kalana quarry in central Estonia contain cave and fracture structures filled with calcitic speleothem precipitates of atypical composition. Calcite crystals in dolomitized limestone cave walls have diverse shapes (equant-blocky, bladed and fibrous), but most of the cave walls and speleothems are covered with an up to 10 cm thick crust of microcrystalline botryoidal calcite. The morphology of precipitates suggests their formation in low hydrodynamic conditions in water supersaturated with calcite. Calcite in speleothems is associated with the mineralization of sulphur-bearing minerals, such as pyrite and abundant barite. Unlike that of speleothem calcite, the stable isotope composition of authigenic calcite shows extreme depletion in 13C and large variations in δ13CPDB from –11 to –56‰, whereas the δ18OPDB values range from –5 to –12‰, suggesting calcite precipitation from a 13C-depleted carbon source supplied by microbially mediated anaerobic oxidation of methane and/or other hydrocarbons at elevated temperatures (up to 70°C). Systematic variation in the δ13CPDB and δ18OPDB values of layered precipitates indicates a change from an initially biogenic methane source to an either thermogenic methane or hydrocarbon source in the low-temperature hydrothermal fluid. Calcite speleothems in Kalana possibly developed at the mixing front of sulphate-rich seawater or groundwater and low-temperature methane-bearing hydrothermal fluids in the phreatic zone of a hypogenic-hydrothermal (karst) system.

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Offeddu, Francesco Giancarlo, Jordi Cama, Josep Maria Soler und Christine V. Putnis. „Direct nanoscale observations of the coupled dissolution of calcite and dolomite and the precipitation of gypsum“. Beilstein Journal of Nanotechnology 5 (11.08.2014): 1245–53. http://dx.doi.org/10.3762/bjnano.5.138.

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In-situ atomic force microscopy (AFM) experiments were performed to study the overall process of dissolution of common carbonate minerals (calcite and dolomite) and precipitation of gypsum in Na2SO4 and CaSO4 solutions with pH values ranging from 2 to 6 at room temperature (23 ± 1 °C). The dissolution of the carbonate minerals took place at the (104) cleavage surfaces in sulfate-rich solutions undersaturated with respect to gypsum, by the formation of characteristic rhombohedral-shaped etch pits. Rounding of the etch pit corners was observed as solutions approached close-to-equilibrium conditions with respect to calcite. The calculated dissolution rates of calcite at pH 4.8 and 5.6 agreed with the values reported in the literature. When using solutions previously equilibrated with respect to gypsum, gypsum precipitation coupled with calcite dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the calcite surface, forming arrow-like forms parallel to the crystallographic orientations of the calcite etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of calcite, indicating the dissolution rate to be the rate-controlling step. The resulting gypsum coating partially covered the surface during the experimental duration of a few hours.

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