Artificial mixed carbonates in the CaCO3?MgCO3 series

Érenburg, B. G.

doi:10.1007/bf00750994

Cited by 4 publications

(5 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Many of the proposed calibrations for determining the Mg-content published in the past were based on single peak displacement (Chave 1952;Goldsmith et al 1955) or on lattice parameter, cell volume, or c/a ratio variations (Goldsmith and Graf 1958;Goldsmith et al 1961;Érenburg 1961). Bischoff et al (1983) and Mackenzie et al (1983) were the first to provide a calibration based on lattice parameters determined by a leastsquares regression analysis.…”

Section: Calibration Of the Mg-content Determination In Calcites Withmentioning

confidence: 99%

“…Determination of Mg-content of calcite by means of XRD patterns has been a well-established method since the 1960s (Chave 1952;Harker and Tuttle 1955;Goldsmith et al 1955Goldsmith et al , 1961Goldsmith and Graf 1958;Érenburg 1961;Glover and Sippel 1967;Althoff 1977;Bischoff et al 1983;Mackenzie et al 1983). The method is based on Vegard's law, which states that, in perfect solid solution, the cell dimensions vary linearly with the composition.…”

Section: Mg Determination In Mgcc By Xrdmentioning

confidence: 99%

“…A new calibration for the Mg quantification in biogenic calcite (in this study echinoderms are used) is presented by applying the Rietveld method to refine lattice parameters and to quantify the MgCc phases (e.g., Rietveld 1969). The calibration, achieved in this way, is compared to available calibrations (e.g., Chave 1952;Goldsmith et al 1955;Goldsmith and Graf 1958;Érenburg 1961;Goldsmith et al 1961;Althoff 1977;Bischoff et al 1983;Mackenzie et al 1983). Furthermore, it is evaluated the degree to which two different MgCc phases within a single sample can be differentiated by XRD and how reliable the phase quantification and Mg-content determination of said sample will be.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Magnesium quantification in calcites [(Ca,Mg)CO3] by Rietveld-based XRD analysis: Revisiting a well-established method

Titschack

Goetz-Neunhoeffer

Neubauer

2011

American Mineralogist

View full text Add to dashboard Cite

Mg-calcites commonly occur in natural environments, with Mg-contents ranging between about 0 and 32 mol% (referring to MgCO 3 ). Often, different Mg-calcite phases occur within the same sample. The Mg-content in calcites permits the classification of the diagenetic environment (marine vs. meteoric), or the reconstruction of paleotemperatures from skeletal remains. Since the 1960s, there have been published various calibrations for Mg determination in calcites based on XRD measurements. Recently, this method has come to be superseded by wet chemical, laser ablation, and microprobe analysis, due to their higher accuracy and/or higher sample resolution of these latter methods.This study presents a new calibration for the Mg determination in calcites using XRD measurements analyzed by means of the Rietveld refinement method. The calibration is based on lattice parameters and exhibits a reliable Mg-determination accuracy of more than 0.8 mol% between 0 and 15.5 mol%. The incorporation of the calibration into the Rietveld refinement software TOPAS permits a fast, standardized workflow. This, in turn, enhances the user-friendliness and the reproducibility of results, as well as allows the simultaneous analysis of multiple Mg-calcites in a sample. Mixtures of two Mg-calcites were analyzed using this new method. The Mg-content of two co-occurring Mg-calcite phases can be reliably quantified providing the Mg-calcites differ by at least 4.9 mol% and the minor Mg-calcite phase makes up more than 2.7 wt%. If the Mg-calcite phases differ by 3.4 mol% or less, the reliable identification of different Mg-calcite phases is questionable, due to the fact that differences involved here are too small. If such XRD patterns are refined with only one Mg-calcite phase, then the systematic misfit between measured and refined pattern can be used for the identification of a second Mg-calcite phase down to a difference in the Mg-content of about 3 mol%. However, a reliable phase quantification for these patterns cannot be achieved.

show abstract

Section: Calibration Of the Mg-content Determination In Calcites Withmentioning

confidence: 99%

Section: Mg Determination In Mgcc By Xrdmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Magnesium quantification in calcites [(Ca,Mg)CO3] by Rietveld-based XRD analysis: Revisiting a well-established method

Titschack

Goetz-Neunhoeffer

Neubauer

2011

American Mineralogist

View full text Add to dashboard Cite

show abstract

“…Our data, based mostly on data of Goldsmith et al [23] and Zhang et al [38], extends the linear relation continuously up to 0.287 apfu of Mg. Comparison of the results of our study with different calibrations [22][23][24]26,27,30,32,42] for determination of the molar fraction of MgCO 3 in calcite shows that the new calibration is in agreement with the trend of the former publications (Figure 10), except for the c/a relation, as already observed by Titschack et al [32]. Some authors validate this linear relationship only up to 0.18 apfu of Mg [20,27], stating that the relation is not linear any more above this content.…”

Section: Discussionmentioning

confidence: 99%

Mineral Quantification with Simultaneous Refinement of Ca-Mg Carbonates Non-Stoichiometry by X-ray Diffraction, Rietveld Method

2017

View full text Add to dashboard Cite

Quantitative phase analyses of carbonate rocks containing Mg-rich calcite and non-stoichiometric dolomite by the Rietveld method yielded improved results when the substitutions are refined for either minerals. The refinement is constrained by the c-axis of the lattice for both minerals using the formula c = −1.8603 nMg + 17.061 for calcite, where nMg is the molar fraction of Mg replacing Ca, and c = 16.0032 + 0.8632∆n Ca for dolomite, with ∆n Ca being the excess Ca in its B site. The one-step procedure was implemented into the Topas software and tested on twenty-two carbonate rock samples from diverse geological settings, considered analogues to petroleum system lithotypes of the pre-evaporite deposits of Southeastern Brazil. The case study spans over a wide range of calcite and dolomite compositions: up to 0.287 apfu Mg in magnesian calcite, and Ca in excess of up to 0.25 apfu in non-stoichiometric dolomite, which are maximum substitutions the formulas support. The method overcomes the limitations for the quantification of minerals by stoichiometry based on whole-rock chemical analysis for complex mineralogy and can be employed for multiple generations of either carbonate. It returns the mineral quantification with unprecedented detailing of the carbonates' composition, which compares very well to spot analysis (both SEM-EDS and EMPA) if those cover the full range of compositions. The conciliation of the quantification results based on the XRD is also excellent against chemical analysis, thermogravimetry, and carbon elemental analysis.

show abstract

“…Mg-calcite with Mg contents higher than 10 mol % is thermodynamically metastable under ambient conditions . Single-phase crystals can be synthesized under high temperature and high pressure. , Despites this fact, Mg-calcite represents the second most important mineral in marine environments. It occurs in marine skeletal hard parts and cements. − Mg-calcite produced by marine organisms is a biomineral, i.e., a mineral formed by living organisms.…”

Section: Introductionmentioning

confidence: 99%

Thermally Induced Modifications and Phase Transformations of Red Coral Mg-Calcite Skeletons from Infrared Spectroscopy and High Resolution Synchrotron Powder Diffraction Analyses

Floquet

Vielzeuf

Ferry

et al. 2015

Crystal Growth & Design

View full text Add to dashboard Cite

Thermal modifications and decomposition of synthetic Mg-calcite and biogenic red coral skeletons are studied using thermogravimetry coupled with differential thermal analysis, infrared spectroscopy, and high temperature synchrotron powder diffraction. Synthetic Mg-calcite with 10 mol % Mg is stable up to 1073 K in self-controlled CO2, with no phase transformation, a parabolic thermal expansion of the c cell parameter, and noticeably, a nonmonotonic thermal variation of the a cell parameter with a minimum at 673 K. By contrast, biogenic Mg-calcite in the range of 9–15 mol % Mg in the red coral skeletons undergoes anomalous structural modifications prior to a phase transformation at 823 K. The thermally induced structural modifications occur concomitantly to degradation and release of organic molecules occluded within the structure. In the range 423–623 K, the c parameter dilatation increases, leading to the anisotropic increase of (18 ± 11) % in branches and (43 ± 3) % in sclerites of the cell volume expansion. Conversely, from 623 to 823 K, the c parameter dilatation highly decreases, corresponding to the anisotropic decrease of (36 ± 3) % in branches and (60 ± 19) % in sclerites. The relative unit cell contraction, Δa/a = −1.1 × 10–4 and Δc/c = −4.3 × 10–4, measured at ambient in red coral skeletons annealed at 823 K is attributed to the native trace elements such as sulfate evidenced by FTIR analyses. The thermal decomposition starts in the range 823–923 K. The formation of lower Mg-calcite phases as intermediate phases supports the direct formation of calcite via a gradual release of Mg2+ ions to form calcite and periclase. The produced calcite is 400 ± 40 nm in size and shows a c-elongated unit cell than can be ascribed to lattice defects due to incorporated strontium and inorganic sulfate ions. Differences in decomposition steps and degree of conversion observed between branches and sclerites are responses to microstructural and chemical features (size, shape, hierarchical organization, and main trace elements Na, S, Sr, P, K) that are distinct in branches and sclerites. As important additional findings, the XRD-based calibration curves used to determine the Mg content in Mg-calcites are not applicable to biogenic Mg-calcites but efficient to evidence their anisotropic distortion compared to geologic or synthetic calcites.

show abstract

Artificial mixed carbonates in the CaCO3?MgCO3 series

Cited by 4 publications

References 5 publications

Magnesium quantification in calcites [(Ca,Mg)CO3] by Rietveld-based XRD analysis: Revisiting a well-established method

Magnesium quantification in calcites [(Ca,Mg)CO3] by Rietveld-based XRD analysis: Revisiting a well-established method

Mineral Quantification with Simultaneous Refinement of Ca-Mg Carbonates Non-Stoichiometry by X-ray Diffraction, Rietveld Method

Thermally Induced Modifications and Phase Transformations of Red Coral Mg-Calcite Skeletons from Infrared Spectroscopy and High Resolution Synchrotron Powder Diffraction Analyses

Contact Info

Product

Resources

About