A relationship between d104 value and composition in the calcite-disordered dolomite solid-solution series

Zhang, Fangfu; Xu, Huifang; Konishi, Hiromi; Roden, Eric E.

doi:10.2138/am.2010.3414

Cited by 131 publications

(131 citation statements)

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“…TEM and SAED analyses were carried out using a Philips CM 200UT microscope (with a spherical aberration coefficient of 0.5 mm and a point-topoint resolution of 0.19 nm). TEM-based EDS analyzer (NORAN Voyager) was also used to measure the content ratio of MgCO 3 to CaCO 3 in the thin specimen of each sample, and the method has been described in detail elsewhere (47). Cliff-Lorimer k factors for Mg and Ca were obtained using a well-characterized dolomite standard from Delight (49.43 mol % CaCO 3 , 50.48 mol % MgCO 3 , and 0.09 mol % FeCO 3 by electron microprobe analyses).…”

Section: Methodsmentioning

confidence: 99%

Testing the cation-hydration effect on the crystallization of Ca–Mg–CO ₃ systems

Yan

Zhang

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

146

134

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Dolomite and magnesite are simple anhydrous calcium and/or magnesium carbonate minerals occurring mostly at Earth surfaces. However, laboratory synthesis of neither species at ambient temperature and pressure conditions has been proven practically possible, and the lack of success was assumed to be related to the strong solvation shells of magnesium ions in aqueous media. Here, we report the synthesis of MgCO 3 and Mg x Ca (1−x) CO 3 (0 < x < 1) solid phases at ambient conditions in the absence of water. Experiments were carried out in dry organic solvent, and the results showed that, although anhydrous phases were readily precipitated in the water-free environment, the precipitates' crystallinity was highly dependent on the Mg molar percentage content in the solution. In specific, magnesian calcite dominated in low [Mg 2+ (1−x) CO 3 were formed. These findings exposed a previously unrecognized intrinsic barrier for Mg 2+ and CO 3 2− to develop long-range orders at ambient conditions and suggested that the long-held belief of cation-hydration inhibition on dolomite and magnesite mineralization needed to be reevaluated. Our study provides significant insight into the long-standing "dolomite problem" in geochemistry and mineralogy and may promote a better understanding of the fundamental chemistry in biomineralization and mineral-carbonation processes.sedimentary geology | carbon sequestration | nonaqueous solvent R arely is there a geological challenge that has endured as long a search for answers as the "dolomite problem" has. Identified more than 220 y ago by the French mineralogist Déodat de Dolomieu, the calcium magnesium carbonate mineral known as dolomite [CaMg(CO 3 ) 2 ] has since been synthesized repeatedly but exclusively at high-temperature and, in some instances, highpressure conditions (1-4). However, in many cases other than igneous-originated carbonatite and deep-burial dolomitization, the formation of dolomitic phases (e.g., microbial and cave deposits) are certainly not associated with such high-temperature and/or -pressure environments (5-8). This obvious discrepancy, compounded by the sharp contrast of massive ancient dolomite formations to the scarcity of modern observations, prompted an arduous search for answers for the past two centuries and, because of a lack of success, has been referred to as the dolomite problem (6, 9-16). Our inability to form dolomite at ambient conditions is hardly the only challenge in mineralogy; a similar situation exists in the case of pure magnesium carbonate [magnesite (MgCO 3 )], which has posed the same level of difficulty to nucleate and grow at room temperature and atmospheric pressure in laboratories but frequently occurs in natural sedimentary settings at earth (sub)surfaces. Interestingly, both dolomite and magnesite belong to the mineral class of anhydrous carbonates. Thus, it becomes logical to surmise that the dolomite problem and the magnesite problem probably share the same root, that is, the difficulty to incorporate unhydrated magnesium ions i...

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Section: Methodsmentioning

confidence: 99%

Testing the cation-hydration effect on the crystallization of Ca–Mg–CO ₃ systems

Yan

Zhang

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

146

134

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“…3 Variation of the a 0 and c 0 cell parameters (a) with Mg-content in Mg-calcite having a disordered distribution of cations, based on Zhang et al (2010), and (b) with Ca-content in dolomite, based on Turpin et al (2012) tion of the cell parameters is almost linear for disordered structures with a MgCO 3 content between 0 and 30% (Reeder and Sheppard 1984;Zhang et al 2010). Thus, for modeling the Mg-calcite 104 peak we derived the relationship between a 0 and c 0 from the empirical curve obtained by Zhang et al (2010) (Fig. 3a), and simply converted the observed 104 d-spacings into compositions.…”

Section: Central European Geology 57 2014mentioning

confidence: 99%

“…Synthetic Mg-calcites with completely disordered arrangements of Ca and Mg ions have significantly larger cell parameters than dolomite (Zhang et al 2010) (Fig. 3a).…”

Section: Central European Geology 57 2014mentioning

confidence: 99%

Distribution and composition of Mg-calcite and dolomite in the water and sediments of Lake Balaton

Tompa

Nyírő-Kósa

Rostási

et al. 2014

Central European Geology

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Lake Balaton is a large and shallow lake that is of great economic and cultural importance in landlocked Hungary. Even though the lake has been studied extensively in the last century from a large number of scientific aspects, the mineralogy of its sediments has not been fully explored. The mud at the bottom of the lake consists mostly of silt-sized grains of carbonate minerals with compositions between those of calcite (CaCO 3 ) and dolomite CaMg (CO 3 ) 2 . In order to understand the processes of carbonate precipitation and the influence of water budget fluctuations on the mineralogical character of the sediment, we used X-ray powder diffraction to analyze the changes of cell parameters of carbonate minerals in the upper half meter of the sediment. The major carbonate phase is Mg-calcite that shows a distinct reduction in cell parameters from west to east, reflecting an increase of its Mg-content, in parallel with a gradient of dissolved Mg/Ca ratio in the water. Intriguingly, dolomite, the other widespread carbonate phase in the sediment, also shows a change in cell parameters from west to east, with the deviations from values of stoichiometric dolomite being largest in the Eastern Basin of the lake. The similar pattern of cell parameter changes of Mg-calcite and dolomite suggests that ordered dolomite with slightly anomalous, Ca-rich composition also forms in the lake, probably by direct precipitation from the water. In contrast, protodolomite forms within the sediment through diagenetic processes. Based on our X-ray powder diffraction measurements, we propose a model of carbonate mineral formation and transformation in Lake Balaton. Since the Mg/Ca ratio of the water appears to be the major factor in controlling the compositions of carbonate minerals, and this ratio in turn is governed by the amount of water supply, the properties of the precipitating carbonate minerals are affected by the actual level of the lake water.

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“…Differences in ionic sizes between substitute and host cations lead to systematic variations in unit-cell parameters and inter-planar spacings that can be measured using XRD. This approach has been widely used in analyzing rhombohedral Ca-Mg carbonates, for example, the composition of biogenic and inorganic (Ca, Mg)CO 3 crystals are often calculated by comparing the difference in d 104 value with the published determinative curves (Zhang et al, 2010;Raz et al, 2000; Falini et al, 1996; Bischoff et al, 1983;Milliman et al, 1971). At least five empirical curves are currently known in the literature (Bischoff et al, 1983;Milliman et al, 1971;Goldsmith et al, 1961Goldsmith et al, , 1955Goldsmith and Graf, 1958; Chave, 1952).…”

Section: Introductionmentioning

confidence: 99%

Metamorphic temperature investigation of coexisting calcite and dolomite marble––examples from Nikani Ghar marble and Nowshera Formation, Peshawar Basin, Pakistan

et al. 2016

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INTRODUCTIONDetermining peak metamorphic temperature of low grade rocks has always been a challenge. X-ray diffraction (XRD) is an established technique for the determination of constituent phases in solid-solution series. Differences in ionic sizes between substitute and host cations lead to systematic variations in unit-cell parameters and inter-planar spacings that can be measured using XRD. This approach has been widely used in analyzing rhombohedral Ca-Mg carbonates, for example, the composition of biogenic and inorganic (Ca, Mg)CO 3 crystals are often calculated by comparing the difference in d 104 value with the published determinative curves (Zhang et al., 2010;Raz et al., 2000; Falini et al., 1996; Bischoff et al., 1983;Milliman et al., 1971). At least five empirical curves are currently known in the literature (Bischoff et al., 1983;Milliman et al., 1971;Goldsmith et al., 1961Goldsmith et al., , 1955Goldsmith and Graf, 1958; Chave, 1952). Determinative curves based on synthetic magnesian calcite crystals are probably the most widely used (Milliman et al., 1971;Goldsmith et al., 1961;Goldsmith and Graf, 1958).Owing to the abundance of calcite and dolomite in the Earth's crust, knowledge of their limits of stability can be used to assess the conditions of temperature prevailing during their formation and subsequent metamorphism. The calcite-dolomite solvus in the system CaCO 3 -MgCO 3 was first investigated by Graf and Goldsmith (1955) and Harker and Tuttle (1955). They recognized that the temperature dependence of the amount of MgCO 3 in calcite in equilibrium with dolomite is potentially a precise method of estimating metamorphic temperatures. Goldsmith (1958, 1955) and Goldsmith et al., (1955) used XRD to determine the MgCO 3 content in natural and synthetic samples to establish phase relationships in the CaO-MgO-CO 2 system from the concentration of 0 to 15 mol.% of MgCO 3 . Later on, calcite-dolomite thermometry has been widely used (e.g., Wada and Suzuki, 1983; Bowman and Essene, 1982;Iii et al., 1982;Nesbitt and Essene, 1982;Ralph and Diane, 1980;Rice, 1977;Suzuki, 1977;Puhan, 1976;Hatcher et al., 1973; Hutcheon and Moore, 1973;Sobol, 1973). Talantsev (1978Talantsev ( , 1976, Bickle and Powell (1977), and Barron (1974) evaluated the effect of FeCO 3 on calcitedolomite thermometry and reported that its effect is negligible at concentrations <1 mol.%. Bickle and Powell (1977) reported that the metamorphic temperature of coexisting calcitedolomite samples from the Glockner area of the Tauern Window, Austria ranged from 410 to 490 o C. The solvus temperature determined from XRD data for Grenville calcite ranged from 415 to 485 o C (Sheppard, 1966). Höy (1970) estimated a temperature of 600 o C by using the calcite from brucite marble.

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A relationship between d104 value and composition in the calcite-disordered dolomite solid-solution series

Cited by 131 publications

References 16 publications

Testing the cation-hydration effect on the crystallization of Ca–Mg–CO ₃ systems

Testing the cation-hydration effect on the crystallization of Ca–Mg–CO ₃ systems

Distribution and composition of Mg-calcite and dolomite in the water and sediments of Lake Balaton

Metamorphic temperature investigation of coexisting calcite and dolomite marble––examples from Nikani Ghar marble and Nowshera Formation, Peshawar Basin, Pakistan

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A relationship between d104 value and composition in the calcite-disordered dolomite solid-solution series

Cited by 131 publications

References 16 publications

Testing the cation-hydration effect on the crystallization of Ca–Mg–CO 3 systems

Testing the cation-hydration effect on the crystallization of Ca–Mg–CO 3 systems

Distribution and composition of Mg-calcite and dolomite in the water and sediments of Lake Balaton

Metamorphic temperature investigation of coexisting calcite and dolomite marble––examples from Nikani Ghar marble and Nowshera Formation, Peshawar Basin, Pakistan

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Testing the cation-hydration effect on the crystallization of Ca–Mg–CO ₃ systems

Testing the cation-hydration effect on the crystallization of Ca–Mg–CO ₃ systems