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Cited by 445Calcium Carbonate Crystallization and InhibitionGeochemistry and Elemental AnalysisGeological formations and processes

Mg/Ca Ratio and Salinity: Two Controls over Crystallization of Dolomite

Folk, Robert L., Land, Lynton S.·1975·AAPG Bulletin
DOI 10.1306/83d91c0e-16c7-11d7-8645000102c1865d
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Abstract

Carbonate precipitation is governed by both thermodynamic and kinetic considerations. The concentration and ionic composition of natural solutions influence not only the mineralogy of the precipitate, but also the crystal size and habit of both metastable and stable phases. Under marine conditions sparry calcite does not precipitate because of poisoning of sideward crystal growth by Mg, which forces Mg-calcite and aragonite to assume a micritic, steep-rhombic, or fibrous habit. Blocky calcite can form only in low Mg/Ca waters, either from primary meteoric solutions, or where Mg has been removed from marine water by dolomite or clays. In hypersaline environments precipitation is commonly rapid and, together with the high concentrations of foreign ions, it is difficult for dolomite to form because of the precise Ca-Mg ordering required. Instead, aragonite or Mg-calcite crystallizes. Dolomite can form only if the Mg/Ca ratio exceeds 5-10:1, and even then it is aphanitic and poorly ordered. At progressively reduced salinities dolomite is able to nucleate at still lower Mg/Ca ratios, approaching 1:1 in meteoric waters. The absence of foreign ions and slow crystallization, commonly under phreatic conditions, cause both dolomite and calcite to form exquisitely limpid, euhedral rhombs. Thus, dolomite probably forms most readily by a reduction in salinity, particularly in a schizohaline environment (alternating between hypersaline and near-fresh conditions, as in a floodable sabkha or…

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  • Carbonate precipitation is controlled by both kinetic and thermodynamic considerations.

    “Carbonate precipitation is controlled by both kinetic and thermodynamic considerations [12].”

    From Thermodynamic and Kinetic Studies of Dolomite Formation: A Review (2023) · cites this paper as [12]

  • In modern hypersaline environments biogenic proto-dolomite forms at ambient to moderately high temperatures (27-50°C), high alkalinities (up to 500 mM), and high-Mg:Ca concentration ratios (>1:1 to 100:1).

    “In such environments biogenic proto-dolomite forms at ambient to moderately high temperatures (e.g., alkaline lakes or shabkhas T between 27-50 ° C), high alkalinities (up to 500 mM), and high-Mg:Ca concentration ratios (>1:1 to 100:1) (Folk and Land 1975; Last and De Deckker 1990; Meister et al. 2011 and references therein).”

    From A route for the direct crystallization of dolomite (2015) · cites this paper as Folk and Land 1975

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Authors
Folk, R. L., & Land, L. S.
Affiliations
Austin, Texas 78712
Venue
AAPG Bulletin
Publisher
American Association of Petroleum Geologists AAPG/Datapages
Published
1975-01-01
Volume
59
Issue
1
Pages
60-68
ISSN
  • 0149-1423 (ISSN-L)
  • 1558-9153
DOI
10.1306/83d91c0e-16c7-11d7-8645000102c1865d
OpenAlex
W2132147684
Cited by
445
References
37
Citations by year
2026: 1 · 2025: 8 · 2024: 8 · 2023: 13 · 2022: 8 · 2021: 17 · 2020: 16 · 2019: 15 · 2018: 8 · 2017: 20 · 2016: 17 · 2015: 13 · 2014: 8 · 2013: 7 · 2012: 7
FWCI
7.97
Type
journal article
Language
en
Open access
closed
Locations
AAPG Bulletin (publishedVersion)
Topics
  • Physical Sciences › Materials Science › Biomaterials › Calcium Carbonate Crystallization and Inhibition
  • Physical Sciences › Earth and Planetary Sciences › Geochemistry and Petrology › Geochemistry and Elemental Analysis
  • Physical Sciences › Earth and Planetary Sciences › Earth-Surface Processes › Geological formations and processes
Keywords
Mg/Ca ratio, salinity, carbonate precipitation, Mg-calcite, aragonite, sparry calcite, crystal morphology, nucleation, sabkha, hypersaline water, meteoric water, coexisting ions

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