Aragonite

Source: Wikipedia, the free encyclopedia.
Aragonite
2V angle
Measured 18–19°
DispersionWeak
ExtinctionParallel
Ultraviolet fluorescenceFaint white-blue to blue-violet
SolubilitySoluble 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

crystal forms of calcium carbonate (CaCO3), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation from marine and freshwater
environments.

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

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

Aragonite, Utah (now a ghost town).[11]

Massive deposits of

Bahamas.[12]

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

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

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

metastable at ambient conditions typical of Earth's surface, and decomposes even more readily than aragonite.[31][32]

Uses

In

biogenic calcium carbonate.[33]

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

Claims that magnetic water treatment can reduce scaling, by converting calcite to aragonite, have been met with skepticism,[35] but continue to be investigated.[36][37]

Gallery

See also

References

  1. S2CID 235729616
    .
  2. PMID 34876711
    .
  3. ^ "Aragonite Properties, Occurrence » Geology Science". 26 October 2021.
  4. ^ Aragonite, Mindat.org
  5. ISSN 0950-1207
    .
  6. ^
    ISBN 0442276249
    .
  7. ISBN 978-1-43170-084-4
    .
  8. ISBN 978-84-95063-98-4
    .
  9. doi:10.3390/app10134633
    .
  10. ISBN 978-1-4612-3748-8
    .
  11. ISBN 978-0-88150-738-6
    .
  12. S2CID 129571671
    .
  13. ISBN 9780195106916
    .
  14. ISBN 0131547283
    .
  15. ^
    S2CID 4285912
    .
  16. doi:10.1016/j.nimb.2009.07.007
    .
  17. S2CID 130591343
    .
  18. doi:10.5741/GEMS.37.1.4
    . Retrieved 1 August 2021.
  19. S2CID 49232599.[permanent dead link
    ]
  20. PMID 36153366
    .
  21. ISBN 9781444314175
    .
  22. ^ Nesse 2000, p. 337.
  23. doi:10.1016/0016-7037(80)90074-5
    .
  24. doi:10.1080/03115518508618971
    .
  25. 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. S2CID 250059382
    .
  28. ^ Fyfe, W.S. (1964). "Calcite aragonite problem" (PDF). AAPG Bulletin. 48 (4): 526. Retrieved 31 July 2021.
  29. doi:10.1029/JZ067i012p04873
    .
  30. ISBN 0136427103
    .
  31. PMID 25031482
    .
  32. 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. doi:10.1021/es060756j
  35. ^ Krauter, PW; Harrar, JE; Orloff, SP; Bahowick, SM (1996). "Test of a Magnetic Device for Amelioration of Scale Formation at Treatment Facility D" (PDF). Internal Report.
    OSTI 567404
    . Retrieved 2009-12-11.
  36. S2CID 96367372
    .
  37. doi:10.5004/dwt.2010.1549
    .

External links
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