Crystallochemistry and Geochemistry of Dolomite

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Crystallography and Physical Chemistry of Minerals & Nanominerals".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 9933

Special Issue Editors


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Guest Editor
Department of Mineralogy and Crystallography, Complutense University of Madrid, Madrid, Spain
Interests: mineral formation; crystal growth mechanisms; solid solutions; mineral surfaces; atomic force microscopy

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Guest Editor
Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Av. de las Palmeras, 4. 18100 Armilla, Granada, Spain
Interests: dolomite; carbonates; crystal growth; mineral surfaces; mineral reactivity; atomic force microscopy; fluid–mineral interactions

Special Issue Information

Dear Colleagues,

It is our pleasure to announce a Special Issue of Minerals entitled “Crystallochemistry and Geochemistry of Dolomite”. Dolomite, CaMg(CO3)2, is an ubiquitous carbonate mineral in the Earth crust which plays a key role in the carbon and magnesium global cycles. Since its discovery at the end of the 18th century, dolomite as a rock-forming mineral has consistently attracted the interest of researchers. However, and despite the geological and geochemical importance of dolomite, its formation mechanisms in nature are still little known. The lack of an universal explanation for the formation of dolomite in natural aqueous environments and the difficulties in synthesizing this mineral under certain experimental conditions are usually termed as the “dolomite problem”. The aim of this Special Issue is to provide new insights into this longstanding mineralogical problem through novel contributions on crystallochemical and geochemical aspects of dolomite formation, e.g., structure, cation ordering, isotopic composition, surface reactivity, and synthesis experiments.

For this Special Issue, we invite submissions of full papers and reviews from a broad scope of research on dolomite mineral. Potential topics include but are not limited to the keywords listed below.

Dr. Carlos M. Pina
Dr. Carlos Pimentel
Guest Editors

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Keywords

  • Atomic force microscopy
  • Atomistic simulations
  • Carbonates
  • Cation ordering
  • Crystallization
  • Crystallography
  • Dolomite synthesis
  • Electron microscopy (SEM, TEM, EMPA)
  • Geochemical analysis
  • Surface reactivity
  • X-ray diffraction (XRD)

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Published Papers (3 papers)

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Research

15 pages, 1468 KiB  
Article
Relative Contributions of Mg Hydration and Molecular Structural Restraints to the Barrier of Dolomite Crystallization: A Comparison of Aqueous and Non-Aqueous Crystallization in (BaMg)CO3 and (CaMg)CO3 Systems
by Shi Zhou, Yuebo Wang and Henry Teng
Minerals 2021, 11(11), 1214; https://doi.org/10.3390/min11111214 - 30 Oct 2021
Cited by 1 | Viewed by 1952
Abstract
Carbonate mineralization is reasonably well-understood in the Ca–CO2–H2O system but continuously poses difficulties to grasp when Mg is present. One of the outstanding questions is the lack of success in dolomite MgCa(CO3)2 crystallization at atmospheric conditions. [...] Read more.
Carbonate mineralization is reasonably well-understood in the Ca–CO2–H2O system but continuously poses difficulties to grasp when Mg is present. One of the outstanding questions is the lack of success in dolomite MgCa(CO3)2 crystallization at atmospheric conditions. The conventional view holds that hydration retards the reactivity of Mg2+ and is supported by solvation shell chemistry. This theory however is at odds with the easy formation of norsethite MgBa(CO3)2, a structural analogue of dolomite, leading to the premise that crystal or molecular structural constrains may also be at play. The present study represents our attempts to evaluate the separate contributions of the two barriers. Crystallization in the Mg–Ba–CO2 system was examined in a non-aqueous environment and in H2O to isolate the effect of hydration by determining the minimal relative abundance of Mg required for norsethite formation. The results, showing an increase from 1:5 to 6:4 in the solution Mg/Ba ratio, represented a ~88% reduction in Mg2+ reactivity, presumably due to the hydration effect. Further analyses in the context of transition state theory indicated that the decreased Mg2+ reactivity in aqueous solutions was equivalent to an approximately 5 kJ/mol energy penalty for the formation of the activated complex. Assuming the inability of dolomite to crystallizes in aqueous solutions originates from the ~40 kJ/mol higher (relative to norsethite) Gibbs energy of formation for the activated complex, a hydration effect was estimated to account for ~12% of the energy barrier. The analyses present here may be simplistic but nevertheless consistent with the available thermodynamic data that show the activated complex of dolomite crystallization reaction is entropically favored in comparison with that of norsethite formation but is significantly less stable due to the weak chemical bonding state. Full article
(This article belongs to the Special Issue Crystallochemistry and Geochemistry of Dolomite)
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12 pages, 9036 KiB  
Article
Effect of pH Cycling and Zinc Ions on Calcium and Magnesium Carbonate Formation in Saline Fluids at Low Temperature
by Veerle Vandeginste
Minerals 2021, 11(7), 723; https://doi.org/10.3390/min11070723 - 5 Jul 2021
Cited by 4 | Viewed by 3233
Abstract
The formation of dolomite is very challenging in the laboratory under ambient conditions due to kinetic inhibition. The goal of this study was to test the impact of pH cycling and zinc ions on the formation of magnesium-rich carbonates in saline fluids at [...] Read more.
The formation of dolomite is very challenging in the laboratory under ambient conditions due to kinetic inhibition. The goal of this study was to test the impact of pH cycling and zinc ions on the formation of magnesium-rich carbonates in saline fluids at a low temperature. Batch reactor experiments were conducted in two series of pH cycling experiments, one without and one with zinc ions, at 43 °C. The results after 36 diel pH cycles indicate a reaction product assemblage of hydromagnesite, aragonite and magnesite in the experiments without zinc ions, and of magnesite and minor aragonite in the experiments with zinc ions. The presence of zinc ions leads to a decrease in the pH in the acid phase of the cycling experiments, which likely plays a role in the reaction product assemblage. Moreover, the hydration enthalpy and other specific ion effects could be additional factors in the formation of magnesium-rich carbonate. The results show a clear evolution towards increasing incorporation of magnesium in the carbonate phase with cycle number, especially in the experiments with zinc ions, reflecting a ripening process that is enhanced by pH cycling. Hence, repeated pH cycling did not lead to more ordered dolomite (from protodolomite), but rather to the formation of magnesite with 92 mol% MgCO3 after 36 cycles, even though geochemical models indicate a higher saturation index for dolomite than for magnesite. Full article
(This article belongs to the Special Issue Crystallochemistry and Geochemistry of Dolomite)
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9 pages, 2491 KiB  
Article
The Effect of Stoichiometry, Mg-Ca Distribution, and Iron, Manganese, and Zinc Impurities on the Dolomite Order Degree: A Theoretical Study
by Yuliya Zvir, Carlos Pimentel and Carlos M. Pina
Minerals 2021, 11(7), 702; https://doi.org/10.3390/min11070702 - 29 Jun 2021
Cited by 5 | Viewed by 3415
Abstract
The determination of the degree of Mg-Ca order in the dolomite structure is crucial to better understand the process or processes leading to the formation of this mineral in nature. I01.5/I11.0 intensity ratios in the X-ray powder diffractograms are [...] Read more.
The determination of the degree of Mg-Ca order in the dolomite structure is crucial to better understand the process or processes leading to the formation of this mineral in nature. I01.5/I11.0 intensity ratios in the X-ray powder diffractograms are frequently measured to quantify dolomite cation order in dolomites. However, the intensity of diffraction peaks can be affected by factors other than the Mg-Ca distribution in the dolomite structure. The most relevant among these factors are (i) deviations from the ideal dolomite stoichiometry, and (ii) the partial substitution of Mg and Ca atoms by Fe, Mn, and Zn impurities. Using the VESTA software, we have constructed crystal structures and calculated I01.5/I11.0 ratios for dolomites with Mg:Ca ratios ranging from 0.5 to 1.5, and with Fe, Mn, and Zn contents up to 30%. Our results show that both deviations from dolomite ideal stoichiometry and the presence of impurities in its structure lead to a significant decrease in I01.5/I11.0 intensity ratios, an effect which must be considered when cation orders of natural dolomites from different origins are compared. Full article
(This article belongs to the Special Issue Crystallochemistry and Geochemistry of Dolomite)
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