Aragonite

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Aragonite
Aragonite crystal - Los Molinillos, Ceunca, Spain - 4x3.6x3.5cm 100g.jpg
Aragonite from Los Molinillos, Cuenca, Spain, sample width about 4 cm
General
Category Carbonate minerals
Formula
(repeating unit)		 Ca CO3
IMA symbol Arg (not to be confused with arginine) [1]
Crystal system Orthorhombic
Unit cell l a = 4.9598(5) Å, b = 7.9641(9) Å, and c = 5.7379(6) Å at 25 °C [2]
Identification
ColorCan come in a variety of colors, but commonly red or white
Crystal habit Commonly dendritic or pseudo-hexagonal; can also be acicular, tabular, prismatic, coral-like
Twinning Cyclic on {110}, forms pseudohexagonal aggregates. If polysynthetic, forms fine striations parallel to [110].
Cleavage Good on [110], Poor on {110}.
Fracture Subconchoidal
Tenacity Very brittle
Mohs scale hardness3.5–4
Luster Vitreous, waxy, resinous
Streak White
Diaphaneity Transparent to opaque
Specific gravity 2.94
Optical propertiesBiaxial (−)
Refractive index nω = 1.550 nε = 1.650
Birefringence δ = 0.155
2V angle Measured 18–19°
Dispersion Weak
ExtinctionParallel
Ultraviolet fluorescence Faint white-blue to blue-violet
Solubility Soluble in acids, and saltwater (but takes longer)
Common impuritiesCommonly strontium, zirconium, lead
Other characteristicsThermodynamically unstable, Morphs slowly back into calcite
References [3] [4]

Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate ( Ca CO3 ), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation from marine and freshwater environments.

Contents

Aragonite crystal structure AragoniteFromCrystalMaker.png
Aragonite crystal structure

The crystal lattice of aragonite differs from that of calcite, resulting in a different crystal shape, an orthorhombic crystal system with acicular crystal. [5] Repeated twinning results in pseudo-hexagonal forms. Aragonite may be columnar or fibrous, occasionally in branching helictitic forms called flos-ferri ("flowers of iron") from their association with the ores at the Carinthian iron mines. [6]

Occurrence

The type location for aragonite is Molina de Aragón in the Province of Guadalajara in Castilla-La Mancha, Spain, for which it was named in 1797. [7] Aragonite is found in this locality as cyclic twins inside gypsum and marls of the Keuper facies of the Triassic. [8] This type of aragonite deposit is very common in Spain, and there are also some in France. [6]

An aragonite cave, the Ochtinská Aragonite Cave, is situated in Slovakia. [9]

In the US, aragonite in the form of stalactites and "cave flowers" (anthodite) is known from Carlsbad Caverns and other caves. [10] For a few years in the early 1900s, aragonite was mined at Aragonite, Utah (now a ghost town). [11]

Massive deposits of oolitic aragonite sand are found on the seabed in the Bahamas. [12]

P-T Diagram for CaCO3.svg

Aragonite is the high pressure polymorph of calcium carbonate. As such, it occurs in high pressure metamorphic rocks such as those formed at subduction zones. [13]

Aragonite forms naturally in almost all mollusk shells, and as the calcareous endoskeleton of warm- and cold-water corals (Scleractinia). Several serpulids have aragonitic tubes. [14] Because the mineral deposition in mollusk shells is strongly biologically controlled, [15] some crystal forms are distinctively different from those of inorganic aragonite. [16] In some mollusks, the entire shell is aragonite; [17] in others, aragonite forms only discrete parts of a bimineralic shell (aragonite plus calcite). [15] The nacreous layer of the aragonite fossil shells of some extinct ammonites forms an iridescent material called ammolite. [18]

Aragonite also forms naturally in the endocarp of Celtis occidentalis . [19]

The skeleton of some calcareous sponges is made of aragonite.[ citation needed ]

Aragonite also forms in the ocean inorganic precipitates called marine cements (in the sediment) or as free crystals (in the water column). [20] [21] Inorganic precipitation of aragonite in caves can occur in the form of speleothems. [22] Aragonite is common in serpentinites where magnesium-rich pore solutions apparently inhibit calcite growth and promote aragonite precipitation. [23]

Aragonite is metastable at the low pressures near the Earth's surface and is thus commonly replaced by calcite in fossils. Aragonite older than the Carboniferous is essentially unknown. [24]

Aragonite can be synthesized by adding a calcium chloride solution to a sodium carbonate solution at temperatures above 60 °C (140 °F) or in water-ethanol mixtures at ambient temperatures. [25]

Physical properties

Aragonite is a thermodynamically unstable phase of calcium carbonate at any pressure below about 3,000 bars (300,000 kPa) at any temperature. [26] Aragonite nonetheless frequently forms in near-surface environments at ambient temperatures. The weak Van der Waals forces inside aragonite give an important contribution to both the crystallographic and elastic properties of this mineral. [27] The difference in stability between aragonite and calcite, as measured by the Gibbs free energy of formation, is small, and effects of grain size and impurities can be important. The formation of aragonite at temperatures and pressures where calcite should be the stable polymorph may be an example of Ostwald's step rule, where a less stable phase is the first to form. [28] The presence of magnesium ions may inhibit calcite formation in favor of aragonite. [29] Once formed, aragonite tends to alter to calcite on scales of 107 to 108 years. [30]

The mineral vaterite, also known as μ-CaCO3, is another phase of calcium carbonate that is metastable at ambient conditions typical of Earth's surface, and decomposes even more readily than aragonite. [31] [32]

Uses

In aquaria, aragonite is considered essential for the replication of reef conditions. Aragonite provides the materials necessary for much sea life and also keeps the pH of the water close to its natural level, to prevent the dissolution of biogenic calcium carbonate. [33]

Aragonite has been successfully tested for the removal of pollutants like zinc, cobalt and lead from contaminated wastewaters. [34]

See also

Related Research Articles

<span class="mw-page-title-main">Limestone</span> Type of sedimentary rock

Limestone is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO3. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.

<span class="mw-page-title-main">Calcite</span> Calcium carbonate mineral

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses.

<span class="mw-page-title-main">Calcium carbonate</span> Chemical compound

Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. Materials containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is produced when calcium ions in hard water react with carbonate ions to form limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.

<span class="mw-page-title-main">Strontianite</span> Rare carbonate mineral and raw material for the extraction of strontium

Strontianite (SrCO3) is an important raw material for the extraction of strontium. It is a rare carbonate mineral and one of only a few strontium minerals. It is a member of the aragonite group.

<span class="mw-page-title-main">Dolomite (mineral)</span> Carbonate mineral - CaMg(CO₃)₂

Dolomite is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally CaMg(CO3)2. The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite (see Dolomite (rock)). An alternative name sometimes used for the dolomitic rock type is dolostone.

<span class="mw-page-title-main">Speleothem</span> Structure formed in a cave by the deposition of minerals from water

A speleothem is a geological formation made by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depending on their depositional history and environment. Their chemical composition, gradual growth, and preservation in caves make them useful paleoclimatic proxies.

<span class="mw-page-title-main">Ooid</span> Small sedimentary grain that forms on shallow tropical seabeds

Ooids are small, spheroidal, "coated" (layered) sedimentary grains, usually composed of calcium carbonate, but sometimes made up of iron- or phosphate-based minerals. Ooids usually form on the sea floor, most commonly in shallow tropical seas. After being buried under additional sediment, these ooid grains can be cemented together to form a sedimentary rock called an oolite. Oolites usually consist of calcium carbonate; these belong to the limestone rock family. Pisoids are similar to ooids, but are larger than 2 mm in diameter, often considerably larger, as with the pisoids in the hot springs at Carlsbad in the Czech Republic.

<span class="mw-page-title-main">Dolomite (rock)</span> Sedimentary carbonate rock that contains a high percentage of the mineral dolomite

Dolomite (also known as dolomite rock, dolostone or dolomitic rock) is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite, CaMg(CO3)2. It occurs widely, often in association with limestone and evaporites, though it is less abundant than limestone and rare in Cenozoic rock beds (beds less than about 66 million years in age). One of the first geologists to distinguish dolomite from limestone was Déodat Gratet de Dolomieu; a French mineralogist and geologist whom it is named after. He recognized and described the distinct characteristics of dolomite in the late 18th century, differentiating it from limestone.

<span class="mw-page-title-main">Vaterite</span> Calcium carbonate mineral

Vaterite is a mineral, a polymorph of calcium carbonate (CaCO3). It was named after the German mineralogist Heinrich Vater. It is also known as mu-calcium carbonate (μ-CaCO3). Vaterite belongs to the hexagonal crystal system, whereas calcite is trigonal and aragonite is orthorhombic.

<span class="mw-page-title-main">Flowstone</span> Geological phenomenon

Flowstones are sheetlike deposits of calcite or other carbonate minerals, formed where water flows down the walls or along the floors of a cave. They are typically found in "solution caves", in limestone, where they are the most common speleothem. However, they may form in any type of cave where water enters that has picked up dissolved minerals. Flowstones are formed via the degassing of vadose percolation waters.

<span class="mw-page-title-main">Carbonate rock</span> Class of sedimentary rock

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and dolomite rock (also known as dolostone), which is composed of dolomite (CaMg(CO3)2). They are usually classified on the basis of texture and grain size. Importantly, carbonate rocks can exist as metamorphic and igneous rocks, too. When recrystallized carbonate rocks are metamorphosed, marble is created. Rare igneous carbonate rocks even exist as intrusive carbonatites and, even rarer, there exists volcanic carbonate lava.

<span class="mw-page-title-main">Biomineralization</span> Process by which living organisms produce minerals

Biomineralization, also written biomineralisation, is the process by which living organisms produce minerals, often resulting in hardened or stiffened mineralized tissues. It is an extremely widespread phenomenon: all six taxonomic kingdoms contain members that are able to form minerals, and over 60 different minerals have been identified in organisms. Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates. These minerals often form structural features such as sea shells and the bone in mammals and birds.

The carbonate compensation depth (CCD) is the depth, in the oceans, at which the rate of supply of calcium carbonates matches the rate of solvation. That is, solvation 'compensates' supply. Below the CCD solvation is faster, so that carbonate particles dissolve and the carbonate shells (tests) of animals are not preserved. Carbonate particles cannot accumulate in the sediments where the sea floor is below this depth.

<span class="mw-page-title-main">Calcite sea</span> Sea chemistry favouring low-magnesium calcite as the inorganic calcium carbonate precipitate

A calcite sea is a sea in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate. An aragonite sea is the alternate seawater chemistry in which aragonite and high-magnesium calcite are the primary inorganic carbonate precipitates. The Early Paleozoic and the Middle to Late Mesozoic oceans were predominantly calcite seas, whereas the Middle Paleozoic through the Early Mesozoic and the Cenozoic are characterized by aragonite seas.

<span class="mw-page-title-main">Aragonite sea</span> Chemical conditions of the sea favouring aragonite deposition

An aragonite sea contains aragonite and high-magnesium calcite as the primary inorganic calcium carbonate precipitates. The reason lies in the highly hydrated Mg2+ divalent ion, the second most abundant cation in seawater after Na+, known to be a strong inhibitor of CaCO3 crystallization at the nucleation stage. The chemical conditions of the seawater must be notably high in magnesium content relative to calcium (high Mg/Ca ratio) for an aragonite sea to form. This is in contrast to a calcite sea in which seawater low in magnesium content relative to calcium (low Mg/Ca ratio) favors the formation of low-magnesium calcite as the primary inorganic marine calcium carbonate precipitate.

<span class="mw-page-title-main">Mollusc shell</span> Exoskeleton of an animal in the phylum Mollusca

The molluscshell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Not all shelled molluscs live in the sea; many live on the land and in freshwater.

<span class="mw-page-title-main">Amorphous calcium carbonate</span>

Amorphous calcium carbonate (ACC) is the amorphous and least stable polymorph of calcium carbonate. ACC is extremely unstable under normal conditions and is found naturally in taxa as wide-ranging as sea urchins, corals, mollusks, and foraminifera. It is usually found as a monohydrate, holding the chemical formula CaCO3·H2O; however, it can also exist in a dehydrated state, CaCO3. ACC has been known to science for over 100 years when a non-diffraction pattern of calcium carbonate was discovered by Sturcke Herman, exhibiting its poorly-ordered nature.

<span class="mw-page-title-main">Shell growth in estuaries</span>

Shell growth in estuaries is an aspect of marine biology that has attracted a number of scientific research studies. Many groups of marine organisms produce calcified exoskeletons, commonly known as shells, hard calcium carbonate structures which the organisms rely on for various specialized structural and defensive purposes. The rate at which these shells form is greatly influenced by physical and chemical characteristics of the water in which these organisms live. Estuaries are dynamic habitats which expose their inhabitants to a wide array of rapidly changing physical conditions, exaggerating the differences in physical and chemical properties of the water.

<span class="mw-page-title-main">Marine biogenic calcification</span> Shell formation mechanism

Marine biogenic calcification is the production of calcium carbonate by organisms in the global ocean.

Automicrite is autochthonous micrite, that is, a carbonate mud precipitated in situ and made up of fine-grained calcite or aragonite micron-sized crystals. It precipitates on the sea floor or within the sediment as an authigenic mud thanks to physicochemical, microbial, photosynthetic and biochemical processes. It has peculiar fabrics and uniform mineralogical and chemical composition.

References

  1. ↑ Warr, L. N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine . 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. ↑ Dickens, B.; Bowen, J. S. (1971). "Refinement of the Crystal Structure of the Aragonite Phase of CaCO(3)". Journal of Research of the National Bureau of Standards Section A. 75A (1): 27–32. doi:10.6028/jres.075A.004. PMC   6715969 . PMID   34876711.
  3. ↑ "Aragonite Properties, Occurrence » Geology Science". 26 October 2021.
  4. ↑ Aragonite, Mindat.org
  5. ↑ Bragg, William Lawrence (1924-01-01). "The structure of aragonite". Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character. 105 (729): 16–39. Bibcode:1924RSPSA.105...16B. doi: 10.1098/rspa.1924.0002 . ISSN   0950-1207.
  6. 1 2 Sinkankas, John (1964). Mineralogy for amateurs. Princeton, N.J.: Van Nostrand. pp. 371–372. ISBN   0442276249.
  7. ↑ Cairncross, B.; McCarthy, T. (2015). Understanding Minerals & Crystals. Cape Town: Struik Nature. p. 187. ISBN   978-1-43170-084-4.
  8. ↑ Calvo, Miguel (2012). Minerales y Minas de España. Vol. V. Carbonatos y Nitratos. Madrid: Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo. pp. 314–398. ISBN   978-84-95063-98-4.
  9. ↑ Pukanská, Katarína; Bartoš, Karol; Bella, Pavel; Gašinec, Juraj; Blistan, Peter; Kovanič, Ľudovít (4 July 2020). "Surveying and High-Resolution Topography of the Ochtiná Aragonite Cave Based on TLS and Digital Photogrammetry". Applied Sciences. 10 (13): 4633. doi: 10.3390/app10134633 .
  10. ↑ Gonzalez, Luis A.; Lohmann, Kyger C. (1988). "Controls on Mineralogy and Composition of Spelean Carbonates: Carlsbad Caverns, New Mexico". In James, Noel P.; Choquette, Philip W. (eds.). Paleokarst. New York: Springer-Verlag. pp. 81–101. doi:10.1007/978-1-4612-3748-8. ISBN   978-1-4612-3748-8.
  11. ↑ Balaz, Christine (2009). An Explorer's Guide: Utah. Vermont: The Countryman Press. p. 368. ISBN   978-0-88150-738-6.
  12. ↑ Newell, Norman D.; Purdy, Edward G.; Imbrie, John (1960). "Bahamian Oölitic Sand". The Journal of Geology. 68 (5): 481–497. Bibcode:1960JG.....68..481N. doi:10.1086/626683. ISSN   0022-1376. S2CID   129571671.
  13. ↑ Nesse, William D. (2000). Introduction to mineralogy. New York: Oxford University Press. pp. 336–337. ISBN   9780195106916.
  14. ↑ Boggs, Sam (2006). Principles of sedimentology and stratigraphy (4th ed.). Upper Saddle River, N.J.: Pearson Prentice Hall. pp. 161–164. ISBN   0131547283.
  15. 1 2 Belcher, A. M.; Wu, X. H.; Christensen, R. J.; Hansma, P. K.; Stucky, G. D.; Morse, D. E. (May 1996). "Control of crystal phase switching and orientation by soluble mollusc-shell proteins". Nature. 381 (6577): 56–58. Bibcode:1996Natur.381...56B. doi:10.1038/381056a0. S2CID   4285912.
  16. ↑ Chateigner, D.; Ouhenia, S.; Krauss, C.; Belkhir, M.; Morales, M. (February 2010). "Structural distortion of biogenic aragonite in strongly textured mollusc shell layers". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. 268 (3–4): 341–345. Bibcode:2010NIMPB.268..341C. doi:10.1016/j.nimb.2009.07.007.
  17. ↑ Loftus, Emma; Rogers, Keith; Lee-Thorp, Julia (November 2015). "A simple method to establish calcite:aragonite ratios in archaeological mollusc shells: CALCITE:ARAGONITE IN ARCHAEOLOGICAL SHELLS". Journal of Quaternary Science. 30 (8): 731–735. doi:10.1002/jqs.2819. S2CID   130591343.
  18. ↑ Mychaluk, Keith A.; Levinson, Alfred A.; Hall, Russel L. (Spring 2001). "Ammolite: Iridescent fossilized ammonite from southern Alberta, Canada" (PDF). Gems & Gemology. 37 (1): 4–25. doi:10.5741/GEMS.37.1.4 . Retrieved 1 August 2021.
  19. ↑ Wang, Jang; Jahren, A. Hope; Amundsen, Ronald (1996). "Potential For [Carbon 14] Dating Of Biogenic Carbon In Hackberry (Celtis) Endocarps" (PDF). Quaternary Research. 47: 337–343. doi:10.1006/qres.1997.1894. S2CID   49232599.[ permanent dead link ]
  20. ↑ Bialik, Or M.; Sisma-Ventura, Guy; Vogt-Vincent, Noam; Silverman, Jacob; Katz, Timor (24 September 2022). "Role of oceanic abiotic carbonate precipitation in future atmospheric CO2 regulation". Scientific Reports. 12 (1): 15970. doi:10.1038/s41598-022-20446-7. PMC   9509385 . PMID   36153366.
  21. ↑ Tucker, Maurice E. (1990). Carbonate sedimentology. Oxford [England]: Blackwell Scientific Publications. ISBN   9781444314175.
  22. ↑ Nesse 2000, p. 337.
  23. ↑ Bonatti, E.; Lawrence, J.R.; Hamlyn, P.R.; Breger, D. (August 1980). "Aragonite from deep sea ultramafic rocks". Geochimica et Cosmochimica Acta. 44 (8): 1207–1214. Bibcode:1980GeCoA..44.1207B. doi:10.1016/0016-7037(80)90074-5.
  24. ↑ Runnegar, B. (1987). "Shell microstructures of Cambrian molluscs replicated by phosphate". Alcheringa: An Australasian Journal of Palaeontology. 9 (4): 245–257. doi:10.1080/03115518508618971.
  25. ↑ Sand, K.K., Rodriguez-Blanco, J.D., Makovicky, E., Benning, L.G. and Stipp, S. (2012) Crystallization of CaCO3 in water-ethanol mixtures: spherulitic growth, polymorph stabilization and morphology change. Crystal Growth & Design, 12, 842-853. doi : 10.1021/cg2012342.
  26. ↑ Carlson, W.D. (1980). "The calcite–aragonite equilibrium: effects of Sr substitution and anion orientational disorder". American Mineralogist. 65 (11–12): 1252–1262. Retrieved 31 July 2021.
  27. ↑ Ulian, Gianfranco; Valdrè, Giovanni (2022-09-01). "Structural and elastic behaviour of aragonite at high-pressure: A contribution from first-principle simulations". Computational Materials Science. 212: 111600. doi:10.1016/j.commatsci.2022.111600. hdl: 11585/893023 . ISSN   0927-0256. S2CID   250059382.
  28. ↑ Fyfe, W.S. (1964). "Calcite aragonite problem" (PDF). AAPG Bulletin. 48 (4): 526. Retrieved 31 July 2021.
  29. ↑ Kitano, Yasushi; Park, Kilho; Hood, Donald W. (November 1962). "Pure aragonite synthesis". Journal of Geophysical Research. 67 (12): 4873–4874. Bibcode:1962JGR....67.4873K. doi:10.1029/JZ067i012p04873.
  30. ↑ Blatt, Harvey; Middleton, Gerard; Murray, Raymond (1980). Origin of sedimentary rocks (2d ed.). Englewood Cliffs, N.J.: Prentice-Hall. ISBN   0136427103.
  31. ↑ Ni, M.; Ratner, B.D. (2008). "Differentiation of Calcium Carbonate Polymorphs by Surface Analysis Techniques – An XPS and TOF-SIMS study". Surf. Interface Anal. 40 (10): 1356–1361. doi:10.1002/sia.2904. PMC   4096336 . PMID   25031482.
  32. ↑ Kamiya, Kanichi; Sakka, Sumio; Terada, Katsuyuki (November 1977). "Aragonite formation through precipitation of calcium carbonate monohydrate". Materials Research Bulletin. 12 (11): 1095–1102. doi:10.1016/0025-5408(77)90038-1.
  33. ↑ Orr, J. C., et al. (2005) Anthropogenic ocean acidification over the 21st century and its impact on calcifying organisms. Nature 437: 681-686
  34. ↑ Köhler, S., Cubillas, et al. (2007) Removal of cadmium from wastewaters by aragonite shells and the influence of other divalent cations. Environmental Science and Technology, 41, 112-118. doi : 10.1021/es060756j
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