Special Issue "Research on Ikaite—Natural Occurrences and Synthetic Mineral Precipitation"

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 (13 May 2023) | Viewed by 2468

Special Issue Editors

Institute of Earth Sciences, University of Iceland, 101 Reykjavík, Iceland
Interests: geochemistry; fluid-rock reactions; carbonates; ikaite; CO2 sequestration
Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland
Interests: mineral formation; mineral-water interaction processes; carbonate mineralogy and geochemistry

Special Issue Information

Dear Colleagues,

This Special Issue of Minerals focuses on research on the mineral ikaite (CaCO3·6H2O), which despite being metastable is found at several localities around the world. Its formation is linked to aqueous environments, and it precipitates in the whole range of natural aqueous environments from marine to fresh water. Ikaite can precipitate close to the water surface, in sea ice, on the beach and deep within sediments. Oddities such as Greenlandic shrimps and industrial pipelines are other known sites for the growth of ikaite. In general, these localities are characterized by low temperature ranging from below zero to approximately +10 °C. At some localities, ikaite forms solely during the wintertime. Nevertheless, laboratory experiments have found ikaite to precipitate at 25 °C or even higher if certain inhibitors of calcite are present in solution. A great deal of research has focused on the phosphate-inhibiting effects on calcite in connection with ikaite formation, but recent research has shown that other inhibitors of calcite ± aragonite can lead to the precipitation of ikaite, such as the presence of Mg in marine systems. Researchers working on calcium carbonate phases in laboratory experiments often come across ikaite, especially when working at low temperatures as stated above. Because ikaite is a metastable mineral phase at all P-T conditions found on Earth, kinetics is at play when ikaite is forming (i.e., rather than thermodynamics). With this Special Issue, we would like to narrow down what geochemical and perhaps even biogeochemical factors control ikaite formation at localities where ikaite is found in Nature. We must be aware that ikaite might not be the first mineral phase to precipitate, but it could be amorphous calcium carbonate (ACC,) as seen from laboratory experiments. Therefore, it is crucial to add to this Special Issue what these experiments have taught us about the different calcium carbonate phases, and what controls ikaite to form either directly from solution or from ACC, and why ikaite when encountered is favored as a calcium carbonate phase over calcite, aragonite, vaterite, and/or monohydrocalcite(s). For what time intervals can we expect ikaite to remain stable, and what mineral alteration pathways can be expected? As already observed both in nature and in experiments, ikaite does not always transform directly into calcite, but takes other mineral pathways depending on, for example, the chemistry of the aqueous environment or solution, possible temperature or pH changes inflicted on the system, and the rate of these changes. The compiled knowledge of this Special Issue of Minerals will be of importance to anyone working on ikaite and research attempting to use the presence of ikaite or what are believed to be pseudomorphs of ikaite as paleoclimate indicators. A Special Issue on Ikaite is highly called for in order to provide an overview of the multiple factors that can lead to its formation, and what could preserve them to eventually allow them to form pseudomorphs composed of calcite or aragonite.

Dr. Gabrielle J. Stockmann
Dr. Juan Diego Rodríguez-Blanco
Guest Editors

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  • natural occurrences of ikaite worldwide
  • synthetic ikaite mineral precipitation
  • (bio-)geochemical controls on ikaite formation
  • parameters favouring metastable minerals
  • hydrated and amorphous calcium carbonates
  • ikaite as a cold-climate paleo indicator

Published Papers (2 papers)

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Calcium Carbonate Hexahydrate (Ikaite): History of Mineral Formation as Recorded by Stable Isotopes
Minerals 2022, 12(12), 1627; https://doi.org/10.3390/min12121627 - 17 Dec 2022
Cited by 1 | Viewed by 842
Calcium carbonate hexahydrate (ikaite) is a rare mineral that forms as metastable species in the organic-carbon-rich sediments of the King George Basin, Bransfield Strait, Antarctica, as a consequence of early diagenetic decomposition of organic matter under cold water (−1.4 °C) and high pressure [...] Read more.
Calcium carbonate hexahydrate (ikaite) is a rare mineral that forms as metastable species in the organic-carbon-rich sediments of the King George Basin, Bransfield Strait, Antarctica, as a consequence of early diagenetic decomposition of organic matter under cold water (−1.4 °C) and high pressure (200 bar) conditions. Large crystals grow in the sediment immediately below the diagenetic transition between microbial sulfate reduction and methanogenesis at ~320 cm below sea floor (bsf). This process is reflected in the dissolved sulfate, total carbon dioxide, and methane concentrations, as well as in the carbon, hydrogen, and oxygen isotope chemistries of the interstitial fluids and dissolved gases of the host sediment. The ikaite crystal faithfully records in its zonal structure the changing carbon isotope ratio of the total dissolved carbon dioxide pool as it gradually diminishes during methanogenesis (δ13Cikaite = −17.5 to −21.4‰). These changes in the crystal’s host environment follow general Rayleigh carbon isotope fractionation. The oxygen isotopes of the ikaite carbonate (δ18Oikaite = 1.46 to 4.45‰) also show a strong zonal distribution, unrelated to temperature of formation, but perhaps controlled by the degree of recrystallization of ikaite to calcite. The crystal water of the ikaite is depleted 11‰ in 2H/1H (VSMOW) relative to the coexisting interstitial water, which is in excellent agreement with the isotope fractionation of other hydrated minerals. In addition to the in situ temperature and pressure, nucleation of the ikaite crystals in the Bransfield Basin sediments may be induced by the high alkalinity, high phosphate concentrations, and dissolved organic compounds. Intense microbial metabolism generates such compounds; of these, aspartic acid and glutamic acid may play an important role, as they do in biological and extracellular carbonate mineral precipitation. All indications are that low temperatures (such as of polar environments), high calcium carbonate supersaturation caused by interstitial methanogenesis, and a sufficiently large supply of dissolved phosphate and amino acids favor metastable ikaite formation. These conditions, modified by recrystallization, may be preserved in calcite glendonites, thinolites, and other calcitic pseudomorphs derived from ikaite and found throughout the ancient sedimentary record. Full article
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Mineral Changes to the Tufa Columns of Ikka Fjord, SW Greenland
Minerals 2022, 12(11), 1430; https://doi.org/10.3390/min12111430 - 10 Nov 2022
Cited by 1 | Viewed by 843
The submarine tufa columns of Ikka Fjord in Southwest Greenland have been studied during multiple field campaigns since 1995. The fjord contains close to thousand columns previously shown to consist of the metastable carbonate mineral ikaite (CaCO3·6H2O), which requires [...] Read more.
The submarine tufa columns of Ikka Fjord in Southwest Greenland have been studied during multiple field campaigns since 1995. The fjord contains close to thousand columns previously shown to consist of the metastable carbonate mineral ikaite (CaCO3·6H2O), which requires near-freezing conditions to remain stable over longer periods of time. During a field campaign to Ikka Fjord in the summer of 2019, seawater temperatures of 6–9 °C and visual physical changes to the columns were observed. These are the highest recorded seawater temperatures measured in Ikka Fjord in over three decades of research. In response, three selected columns at three different locations were sampled at their bases, middle, and top sections for mineralogical analysis. These samples were supplemented by a four further column samples and an extensive hydrographical campaign during fieldwork in the summer 2021. Here, we report the results of the mineralogical analyses performed by X-ray diffraction and µ-Raman Spectroscopy on these column samples. The results show that the columns analysed now consist of the less hydrated carbonate minerals, monohydrocalcite (CaCO3·H2O), aragonite, and calcite (CaCO3). One of the columns has completely altered into monohydrocalcite, whereas the other columns have crusts of ikaite and cores of monohydrocalcite ± aragonite and calcite. This change is interpreted as a dehydration reaction and mineral alteration from ikaite to monohydrocalcite continuing to aragonite ± calcite in response to being bathed in warming seawater. Hydrographic profilers and static dataloggers recorded seawater temperatures of 4–8 °C in the column-containing fjord areas during June–August 2021. The upper parts of the columns are particularly exposed to temperatures > 6 °C, considered to be the long-term stability threshold of ikaite in Ikka Fjord. The mineral dehydration reactions are irreversible. It is therefore predicted in a warming Arctic, ikaite will only appear as new growth on the columns for a short period, and that with time, the columns of Ikka Fjord will change mineralogy into mainly monohydrocalcite. Full article
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