Ikaite is the
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...
name for the hexahydrate of
calcium carbonate
Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
, . Ikaite tends to form very steep or spiky pyramidal crystals, often radially arranged, of varied sizes from
thumbnail size
aggregates to gigantic salient spurs. It is only found in a
metastable
In chemistry and physics, metastability is an intermediate energetic state within a dynamical system other than the system's state of least energy.
A ball resting in a hollow on a slope is a simple example of metastability. If the ball is onl ...
state and decomposes rapidly by losing most of its water content once removed from near-freezing water. This "melting mineral" is more commonly known through its
pseudomorphs.
Distribution
It is usually considered a rare mineral, but this is likely due to difficulty in preserving samples. It was first discovered in nature by the Danish
mineralogist
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical mineralogy, optical) properties of minerals and mineralized artifact (archaeology), artifacts. Specific s ...
Pauly in the
Ikka Fjord in southwest
Greenland
Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...
, close to
Ivittuut, the locality of the famous
cryolite
Cryolite ( Na3 Al F6, sodium hexafluoroaluminate) is a rare mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987.
It is used in the reduction ("smelting") of aluminium, in pest ...
deposit. Here ikaite occurs in truly spectacular towers or columns (up to tall) growing out of the fjord floor towards the surface water, where they are naturally truncated by waves, or unnaturally by the occasional boat.
[ At the Ikka Fjord, it is supposed that the ikaite towers are created as the result of a groundwater seep, rich in carbonate and ]bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial bioche ...
ions, entering the fjord bottom in the form of springs, where it hits the marine fjord waters rich in calcium. Ikaite has also been reported as occurring in high-latitude marine sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
s at Bransfield Strait, Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
; Sea of Okhotsk, Eastern Siberia
Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
, off Sakhalin; and Saanich Inlet, British Columbia
British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
, Canada. In addition, it has been reported in a deep sea fan off the Congo, and therefore probably has a worldwide occurrence. The most recent occurrence has been reported by Dieckmann et al. (2008). They found the mineral ikaite directly precipitated in grain sizes of hundreds of micrometers in sea ice in the Weddell Sea
The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha C ...
and throughout fast ice off Adélie Land
Adélie Land ( ) or Adélie Coast is a Territorial claims in Antarctica, claimed territory of France located on the continent of Antarctica. It stretches from a portion of the Southern Ocean coastline all the way inland to the South Pole. Franc ...
, Antarctica. In addition, ikaite can also form large crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s within sediment that grow to macroscopic size, occasionally with good crystal form. There is strong evidence that some of these marine deposits are associated with cold seeps. Ikaite has also been reported as a cryogenic deposit in caves where it precipitates from freezing carbonate-rich water.
Structure
Ikaite crystallizes in the monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...
crystal system in space group C2/c with lattice parameters a~8.87A, b~8.23A, c~11.02A, β~110.2°. The structure of ikaite consists of an ion pair of (Ca2+CO32−)0 surrounded by a cage of hydrogen-bonded water molecules which serve to isolate one ion pair from another.
Stability
Synthetic ikaite was discovered in the nineteenth century in a study by Pelouze. Ikaite is only thermodynamically stable at moderate pressures, so when found near the Earth's surface is always metastable
In chemistry and physics, metastability is an intermediate energetic state within a dynamical system other than the system's state of least energy.
A ball resting in a hollow on a slope is a simple example of metastability. If the ball is onl ...
. Nevertheless, as it appears to be at least moderately common in nature, it is clear that the conditions for metastable nucleation
In thermodynamics, nucleation is the first step in the formation of either a new Phase (matter), thermodynamic phase or Crystal structure, structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically def ...
and growth cannot be too restrictive. Cold water is certainly required for formation, and nucleation inhibitors like phosphate ions for the growth of anhydrous calcium carbonate
Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
phases, such as calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
, aragonite
Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...
, and vaterite
Vaterite is a mineral, a polymorphism (materials science), polymorph of calcium carbonate (calcium, Cacarbon, Coxygen, O3). It was named after the German mineralogist Heinrich Vater. It is also known as mu-calcium carbonate (μ-CaCO3). Vaterite b ...
probably aid its formation and preservation. It is thought that perhaps the structure of calcium carbonate in a concentrated aqueous solution also consists of an ion pair, and this is why ikaite readily nucleates at low temperatures outside of its thermodynamic stability range. When removed from its natural cold water environment, ikaite rapidly disintegrates into monohydrocalcite or anhydrous calcium carbonate phases and water, earning the nickname of the melting mineral.
Pseudomorphs
The presence of ikaite may be recorded through geological time through the presence of pseudomorphs of other calcium carbonate
Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
phases after it. Although it can be hard to uniquely define the original mineral for every specimen, there appears to be good evidence for ikaite as the precursor for the majority of the following locality names of pseudomorphs:
* Glendonite, after type locality, Glendon, New South Wales, Australia.
* Thinolite, (Gr. Thinos = shore) found in the tufa of Mono Lake
Mono Lake ( ) is a Salt lake, saline soda lake in Mono County, California, formed at least 760,000 years ago as a terminal lake in an endorheic basin. The lack of an outlet causes Hypersaline lake, high levels of salts to accumulate in the lake ...
, California, US
* Jarrowite, Jarrow, Northumberland, UK
* Fundylite, Bay of Fundy, Nova Scotia, Canada
* Gersternkorner, (Ger. = Barleycorn)
* Gennoishi, (Jp. = hammerstones)
* Molekryds, (Dan. = Mole Cross), Mors Island, Jutland, Denmark
* Pseudogaylussite (from semblance to Gaylussite)
* White Sea hornlets, White Sea and Kola peninsula.
Ikaite or its pseudomorphs have been reported as occurring in marine, freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
, and estuarine environments.
The common ingredient appears to be cold temperatures, although the presence of traces of other chemicals, such as nucleation inhibitors for anhydrous calcium carbonate, may also be required. It has also been reported as forming in winter on Hokkaido
is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...
at a saline spring.
Since cold water can be found at depth in the oceans, even in the tropics, ikaite can form at all latitudes. However, the presence of ikaite pseudomorphs can be used as a paleoclimate proxy or paleothermometry representing water near freezing conditions.
Thinolite deposits
Thinolite is an unusual form of calcium carbonate found on the shore (Greek: ''thinos'' = shore) of Mono Lake
Mono Lake ( ) is a Salt lake, saline soda lake in Mono County, California, formed at least 760,000 years ago as a terminal lake in an endorheic basin. The lack of an outlet causes Hypersaline lake, high levels of salts to accumulate in the lake ...
, California
California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
. This and other lakes now largely in the desert or semi-desert environments of the southwestern US were part of a larger post-glacial lake that covered much of the region near the end of the last glaciation. It is thought that at this time, conditions similar to that of the Ikka fjord allowed for the growth of massive ikaite.
Isotope geochemistry
Isotope geochemistry
Isotope geochemistry is an aspect of geology based upon the study of natural variations in the relative abundances of isotopes of various Chemical element, elements. Variations in isotopic abundance are measured by isotope-ratio mass spectrometry, ...
can reveal information about the origin of the elements that make up minerals. The isotopic composition of ikaite and the pseudomorphs is actively studied. Studies of the ratio of 13C to 12C in ikaite relative to a natural, standard ratio can help to determine the origin of the carbon pool (organic/inorganic) which was consumed to form ikaite. Some studies have shown that oxidizing methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
is the source of both modern-day ikaite and glendonites in high-latitude marine sediments. Similarly, the ratio of 18O to 16O, which varies in nature with temperature and latitude, can be used to show that glendonites were formed in waters very close to the freezing point, in agreement with the observed formation of ikaite.
References
Further reading
*
*
* King, C., (1878). U. S. Geological exploration of the fortieth parallel, Vol. 1. Washington: D.C., U. S. Government Printing Office.
* Russell, I.C. (1889). Quaternary history of Mono Valley, California. Reprint from the Eighth Annual Report of the United States Geological Survey, Pages 267–394. Artemisia Press, Lee Vining, California 1984
* Schultz, B.P., Vickers, M.L., Huggett, J., Madsen, H., Heilmann-Clausen, C., Friis, H. & Suess, E. 2020. Palaeogene glendonites from Denmark. Bulletin of the Geological Society of Denmark, Vol. 68, pp. 23–35, https://doi.org/10.37570/bgsd-2020-68-03-rev
* Schultz, B.P., Huggett J.M., Kennedy, G.L., Burger, P., Jensen, A.M., Kanstrup, M., Bernasconi, S.M., Thibault, N., Ullmann, C.V., Vickers, M.L. (2023) Petrography and geochemical analysis of Arctic ikaite pseudomorphs from Utqiagvik (Barrow), Alaska NJG volume 103, https://dx.doi.org/10.17850/njg103-1-3
* Schultz, B.P.; Huggett, J.; Ullmann, C.V.; Kassens, H.; Kölling, M. Links between Ikaite Morphology, Recrystallised Ikaite Petrography and Glendonite Pseudomorphs Determined from Polar and Deep-Sea Ikaite. Minerals 2023, 13, 841, https://doi.org/10.3390/min13070841
* Schultz, B.P.; Huggett, J.; Schootbrugge, B.v.d.; Ullmann, C.V.; Broch, M.C. Transgression Related Holocene Coastal Glendonites from Historic Sites. Minerals 2023, 13, 1159, https://doi.org/10.3390/min13091159
* Whiticar, M.J.; Suess, E.; Wefer, G.; Müller, P.J. Calcium Carbonate Hexahydrate (Ikaite): History of Mineral Formation as Recorded by Stable Isotopes. Minerals 2022, 12, 1627. https://doi.org/10.3390/min12121627
* Tollefsen, E., Balic-Zunic, T., Mörth, CM. et al. Ikaite nucleation at 35 °C challenges the use of glendonite as a paleotemperature indicator. Sci Rep 10, 8141 (2020). https://doi.org/10.1038/s41598-020-64751-5
* Vickers, M.L., Lengger, S.K., Bernasconi, S.M. et al. Cold spells in the Nordic Seas during the early Eocene Greenhouse. Nat Commun 11, 4713 (2020). https://doi.org/10.1038/s41467-020-18558-7
External links
Mineralogical and crystallographic data about ikaite
{{Webarchive, url=https://web.archive.org/web/20061009133026/http://www.minweb.co.uk/carbonates/ikaidata.html , date=2006-10-09
Ikaite homepage
Glendonites and pseudomorphs after ikaite (in German)
* ttps://web.archive.org/web/20080106224839/http://www.glendonite.com/ Pyramidia – Lair of the Rare and Fascinating Glendonite
A study of the type locality of the mineral ikaite
Calcium minerals
Carbonate minerals
Hexahydrate minerals
Monoclinic minerals
Minerals in space group 15