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Iceland spar

From Wikipedia, the free encyclopedia

Iceland spar,formerly calledIceland crystal(Icelandic:silfurberg[ˈsɪlvʏrˌpɛrk],lit. 'silver-rock') and also calledoptical calcite,is a transparent variety ofcalcite,or crystallizedcalcium carbonate,originally brought fromIceland,and used in demonstrating thepolarizationoflight.[1][2]

Formation and composition

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Calcite rhombohedral crystal structure

Iceland spar is a colourless, transparent variety of calcium carbonate (CaCO3).[3]It crystallizes in the trigonal system, typically formingrhombohedral crystals.[4]It has a Mohs hardness of 3 and exhibitsdouble refraction,splitting a ray of light into two rays that travel at different speeds and directions.[3][5]

Iceland spar forms insedimentary environments,mainly limestone and dolomite rocks, but it also forms in hydrothermalveinsandevaporitedeposits.[6]It precipitates from solutions rich in calcium and carbonate ions, influenced by temperature, pressure, and impurities.[6][7]

The most common crystal structure of Iceland spar is rhombohedral, but other structures, such as scalenohedral or prismatic, can form depending on formation conditions.[8][9]Iceland spar is primarily found inIcelandbut can occur in different parts of the world with suitable geological conditions.[3][10]

Characteristics and optical properties

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Calcite crystal birefringence

Iceland spar is characterized by its large, readilycleavablecrystals, easily divided intoparallelepipeds.[11][12]This feature makes it easily identifiable and workable. One of the most remarkable properties of Iceland spar is itsbirefringence,where the crystal'srefractive indexdiffers for light of different polarizations.[11][12]When a ray of unpolarized light passes through the crystal, it is divided into two rays of mutuallyperpendicularpolarization directed at various angles. This double refraction causes objects seen through the crystal to appear doubled.

Iceland spar possesses several optical properties other than double refraction and birefringence. It is highly transparent to visible light, allowing light to pass through with minimal absorption or scattering, which is ideal for optical applications requiring clarity.[13]Iceland spar can produce vivid colours when viewed under polarized light due to its birefringent nature.[14]This effect is known as the "Becke line"and can be used to determine a mineral's refractive index.[15][16]Additionally, Iceland spar is optically active, meaning it can rotate theplane of polarizationof light passing through it, a property resulting from its asymmetrical atomic arrangement.[17]Theseoptical propertiescontribute to the mineral's scientific use and aesthetic appeal.

Historical significance

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Iceland spar holds historical importance in optics and the study of light.[18]One of its most notable properties is its ability to exhibit double refraction.[18]This phenomenon was first described by the Danish scientistErasmus Bartholinin 1669, who observed it in a specimen of Iceland spar.[19]

The study ofdouble refractionin Iceland spar played a role in developing the wave theory of light. Scientists such asChristiaan Huygens,[20]Isaac Newton,andSir George Stokesstudied this phenomenon and contributed to the understanding of light as a wave.[21][22]Huygens, in particular, used double refraction to support his wave theory of light, in contrast to Newton's corpuscular theory.[23]Augustin-Jean Fresnelpublished a complete explanation of double refraction in light polarization in the 1820s.[24]

The understanding of double refraction in Iceland spar also led to the development ofpolarized light microscopy,which is used in various scientific fields to study the properties of materials.[25][26]Iceland spar has been used historically in optical instruments like polarizing microscopes and navigation equipment.[25]

Mining

[edit]

Minesproducing Iceland spar include many mines producing related calcite andaragonite.Iceland spar occurs in various locations worldwide, historically named after Iceland due to its abundance on the island.[27]Other productive sources include China and the greaterSonoran Desertregion, inSanta Eulalia, Chihuahua,Mexico,andNew Mexico,United States.[28][29][30]The clearest specimens, as well as the largest, have been from theHelgustaðir minein Iceland.[31]

Surveying tools and techniques are combined to reduce the risk and cost of exploration to identify deposits.[32]Geological mapsand remote sensing techniques, such assatellite imageryandaerial photography,are used for initial exploration and regional assessment to identify potential areas for further exploration.[32][33]Geophysical surveys,including magnetometry, gravity surveys, and electromagnetic surveys, are then employed to detect anomalies indicating mineralization.[32]Field mapping of surface geology and mineralogy also plays a role in identifying potential mineralization zones.[34]

The mining process for Iceland spar varies based on the specific geological conditions of the deposit.Open-pit miningor quarrying is common for surface deposits.[35]Once extracted, the calcite is processed to removeimpurities,prepared for various applications, including optical instruments and jewelry, and used as a source of calcium carbonate in industries like construction and agriculture.[35][36]

Environmental issues

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Some potential environmental issues associated with Iceland spar mining includehabitat destruction,water pollution,air pollution,soil degradation,and visual impact.[37][38]Mining activities can destroy natural habitats, mainly if the mining site is located in ecologically sensitive areas, leading to the loss ofbiodiversityand disrupting local ecosystems.[37]Water sources can be contaminated through the discharge of chemicals used in the extraction and processing of minerals, impacting aquatic life and water quality.[38]Mining activities can also lead to soil erosion and degradation, mainly if proper land reclamation measures are not implemented after mining ceases.[39]Open-pit mining operations can have a significant visual impact on the landscape, altering the natural scenery of an area.[40]These measures may includeerosion control,environmentally friendly mining techniques, and the reclamation of mined areas to restore them to a natural state.[40]

Health concerns

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Mining, including Iceland spar mining, poses various health risks to workers and nearby communities.[41]Some key health concerns associated with mining activities include respiratory issues,noise-induced hearing loss,chemical exposure,musculoskeletal disorders,injuries and accidents, and mental health issues.[41]Dust generated during mining operations can contain harmful particles, leading to respiratory problems.[41]The high noise levels generated by mining activities can cause hearing loss over time if proper protective measures are not in place.[41]Miners may also be exposed to harmful chemicals used in the extraction and processing of minerals, which can cause various health issues.[41]The physical demands of mining work, such as heavy lifting and repetitive motions, can result in musculoskeletal disorders.[41]Injuries and accidents are also common risks in mining, including falls, equipment-related incidents, and mine collapses.[41]The demanding nature of mining work, along with long hours and isolation, can contribute to mental health issues such as stress, anxiety, and depression.[42]Mining companies must implement health and safety measures to mitigate these risks to protect workers and nearby communities, including personal protective equipment, dust control measures, and health and safety training.[41]Regularly monitoring air quality, noise levels, and other potential hazards is essential to ensure a safe working environment.[41]

Uses

[edit]
Iceland spar, possibly the Icelandic medieval sun stone used to locate the sun in the sky when obstructed from view[43]

Iceland spar has been historically used in telecommunications due to its unique optical properties.[44]One of its key features, birefringence, made it worthwhile in early optical technologies, such as developing optical instruments like polarizing microscopes and constructing optical rangefinders and gunsights.[44][45]

While uncommon, Iceland spar has historically been used in navigation as a polarizing filter to determine the sun's direction on overcast days.[46]It has been speculated that thesunstone(Old Norse:sólarsteinn,a different mineral from the gem-qualitysunstone) mentioned in medieval Icelandic texts, such asRauðúlfs þáttr,was Iceland spar, and thatVikingsused its light-polarizing property to tell the direction of the sun on cloudy days fornavigationalpurposes.[43][47]The polarization of sunlight in theArcticcan be detected,[46]and the direction of the sun identified to within a few degrees in both cloudy and twilight conditions using the sunstone and the naked eye.[48]The process involves moving the stone across the visual field to reveal a yellowentoptic patternon thefoveaof the eye, probablyHaidinger's brush.The recovery of an Iceland spar sunstone from a ship of theElizabethan erathat sank in 1592 offAlderneysuggests that this navigational technology may have persisted after the invention of the magneticcompass.[49][50]

William Nicol(1770–1851) invented the first polarizing prism, using Iceland spar to create hisNicol prism.[51]

Modern applications

[edit]

Despite being historically significant, Iceland spar still holds an essential place in modern applications. Due to its optical properties, Iceland spar is still used in instruments like polarizing microscopes,lenses,and filters.[52]Iceland spar is also used in optical instruments for geological and biological microscopy as its birefringence helps to reveal material structure.[53]It is also a practical tool used in education and research to demonstrate optical principles.[53]Though its applications are less widespread than in the past, Iceland spar continues to contribute to various scientific and technological endeavours.

As a type of calcite, Iceland spar can be used in construction as a building material incementandconcrete.Its high purity and brightness make it an ideal filler in paints and coatings.[54]In metallurgy, calcite acts as afluxto lower the melting point of metals duringsmeltingand refining.[55]Additionally, it is used in agriculture as asoil conditionerand neutralizer to adjust soil pH levels and improve crop yields.[56]Calcite also contributes to environmental remediation efforts, treating acidic water and soil by neutralizing acidity and removing heavy metals.[56]

Geological significance

[edit]

Due to Iceland spar typically forming in sedimentary environments, particularly limestone and dolomite rocks, its formation is closely tied to these carbonate rocks' deposition anddiagenesis(compaction and cementation).[57]Studying Iceland spar can provide valuable information about past environmental conditions, such as the presence of ancient seas and marine life, as carbonate rocks likelimestoneoften form in marine environments.[58]The presence of Iceland spar can also indicate the presence ofhydrothermal activity,as calcite can form in hydrothermal veins.[59]

Conservation and protection

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Due to their scientific and historical significance, conservation efforts related to Iceland spar primarily focus on preserving specimens and mining sites.[60]One of the challenges in preserving Iceland spar specimens is the risk of damage during extraction, handling, and storage.[61]Mining sites that yield high-quality Iceland spar specimens are also of interest for conservation.[60]These sites may be designated protected areas to preventoverexploitation.[60]

Cultural impact

[edit]

TheThomas PynchonnovelAgainst the Dayuses the doubling effect of Iceland spar as a theme.[62]

See also

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References

[edit]
  1. ^Public DomainThis article incorporates text from this source, which is in thepublic domain.Porter, Noah,ed. (1913). "Polarimetry".Webster's Dictionary.Springfield, Massachusetts: C. & G. Merriam Co.
  2. ^"Iceland spar".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)
  3. ^abcKristjansson, Leo (2002)."Iceland Spar: The Helgustadir Calcite Locality and its Influence on the Development of Science".Journal of Geoscience Education.50(4): 419–427.Bibcode:2002JGeEd..50..419K.doi:10.5408/1089-9995-50.4.419.ISSN1089-9995.
  4. ^Hughes, H. Herbert., Iceland spar and optical fluorite:U. S. Bureau of Mines, Information Circular6468 (1931)
  5. ^Wada, Shinobu; Suzuki, Hitomi (2003-01-06)."Calcite and fluorite as catalyst for the Knövenagel condensation of malononitrile and methyl cyanoacetate under solvent-free conditions".Tetrahedron Letters.44(2): 399–401.doi:10.1016/S0040-4039(02)02431-0.ISSN0040-4039.
  6. ^abRollion-Bard, Claire; Marin-Carbonne, Johanna (2011-06-01)."Determination of SIMS matrix effects on oxygen isotopic compositions in carbonates".Journal of Analytical Atomic Spectrometry.26(6): 1285–1289.doi:10.1039/C0JA00213E.ISSN1364-5544.
  7. ^Morse, John W.; Arvidson, Rolf S.; Lüttge, Andreas (2007-02-01)."Calcium Carbonate Formation and Dissolution".Chemical Reviews.107(2): 342–381.doi:10.1021/cr050358j.ISSN0009-2665.PMID17261071.
  8. ^Skomorovsky, Valery; Kushtal, Galina; Tokareva (Lopteva), Lyubov (2022-03-25)."Iceland spar and birefringent filter (BF) development".Solar-Terrestrial Physics.8(1): 69–84.Bibcode:2022STP.....8a..69S.doi:10.12737/stp-81202209.ISSN2500-0535.
  9. ^Skropyshev, A. V. (1959)."Gaseous-Liquid Inclusions in Crystals of Iceland Spar".International Geology Review.1(9): 1–11.Bibcode:1959IGRv....1R...1S.doi:10.1080/00206815909473436.ISSN0020-6814.
  10. ^Cook, Robert B. (2009)."Mineral Oddities: Theme of the 2009 Tucson Gem & Mineral Show".Rocks & Minerals.84(1): 16–25.Bibcode:2009RoMin..84...16C.doi:10.3200/RMIN.84.1.16-25.ISSN0035-7529.
  11. ^abPublic DomainThis article incorporates text from this source, which is in thepublic domain.Webster, Noah(1828)."Birefringence".Webster's Dictionary.Springfield, Massachusetts: C. & G. Merriam Co.
  12. ^abMiers, Henry A.,Mineralogy: an introduction to the scientific study of minerals.Nabu Press.ISBN1-177-85127-XChap. 6, p. 128.
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  15. ^Kristjansson, Leo (2002)."Iceland Spar: The Helgustadir Calcite Locality and its Influence on the Development of Science".Journal of Geoscience Education.50(4): 419–427.Bibcode:2002JGeEd..50..419K.doi:10.5408/1089-9995-50.4.419.ISSN1089-9995.
  16. ^Choi, Ju H.; Eichele, Chad; Lin, Yuan C.; Shi, Frank G.; Carlson, Bob; Sciamanna, Steven (2008-03-01)."Determination of effective refractive index of molecular diamondoids by Becke line method".Scripta Materialia.Viewpoint set no. 43 “Friction stir processing”.58(5): 413–416.doi:10.1016/j.scriptamat.2007.10.036.ISSN1359-6462.
  17. ^Kristjánsson, L. (2012-05-16)."Iceland spar and its legacy in science".History of Geo- and Space Sciences.3(1): 117–126.Bibcode:2012HGSS....3..117K.doi:10.5194/hgss-3-117-2012.ISSN2190-5029.
  18. ^abKristjansson, Leo (2002)."Iceland Spar: The Helgustadir Calcite Locality and its Influence on the Development of Science".Journal of Geoscience Education.50(4): 419–427.Bibcode:2002JGeEd..50..419K.doi:10.5408/1089-9995-50.4.419.ISSN1089-9995.
  19. ^Bartholin, Rasmus; Archibald, Thomas; Buchwald, Jed Z.; Møller Pedersen, Kurt (1991).Experiments on Birefringent icelandic crystal: with a facsimile of the original publication 1669.Acta historica scientiarum naturalium et medicinalium (Reprod. en fac-sim. ed.). Copenhagen: the Danish national library of science and medicine.ISBN978-87-7709-010-3.
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  21. ^Public DomainThis article incorporates text from a publication now in thepublic domain:Chambers, Ephraim,ed. (1728). "Isaac Newton".Cyclopædia, or an Universal Dictionary of Arts and Sciences(1st ed.). James and John Knapton, et al.
  22. ^Larmor, Joseph2010. Retrieved January 2, 2011.Memoir and scientific correspondence of the late Sir George Gabriel Stokes, bart., selected and arranged by Joseph Larmor.Nabu Press.ISBN1-177-14275-9p. 269.
  23. ^Huygens, Christiaan (1912).Treatise On Light.Osmania University, Digital Library Of India. Macmillan And Company., Limited.
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  26. ^Skomorovsky, Valery; Kushtal, Galina; Tokareva (Lopteva), Lyubov (2022-03-25)."Iceland spar and birefringent filter (BF) development".Solar-Terrestrial Physics.8(1): 69–84.Bibcode:2022STP.....8a..69S.doi:10.12737/stp-81202209.ISSN2500-0535.
  27. ^Russell, Daniel E. 17 February 2008. Retrieved December 31, 2010. "Helgustadir Iceland Spar Mine"mindat.org
  28. ^Retrieved January 2, 2011. "Calcite"Granite Gap"Several variety names exist for calcite. Iceland Spar is an ice-clear variety that demonstrates the effect of double refraction or birefringence... Young mountain ranges in Mexico and South America also host fine localities for calcite. They include Chihuahua, Chihuahua; the Santa Eulalia Dist., Chihuahua; Mapimí, Durango; Guanajuato, Guanajuato; and Charcas, San Luis Potosí; all Mexico"
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  30. ^WANG Jing-teng, CHEN Hen-shui, YANG En-lin, WU Bo. 2009. Retrieved January 3, 2011. "Geological Characteristics of Iceland Spar Mineral Deposit of Mashan District in Guizhou".China National Knowledge Infrastructure,P619.2CNKI:SUN:KJQB.0.2009-33-061
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  38. ^abSaliu, Muyideen Alade; Shehu, Shaib Abdulazeez (2012). "Effects of Calcite and Dolomite Mining on Water and Soil Qualities: A case study of Freedom Group of Companies, Ikpeshi, Edo State Nigeria".Journal of Emerging Trends in Engineering and Applied Sciences.3(1): 19–24.
  39. ^Saliu, Muyideen Alade; Shehu, Shaib Abdulazeez (2012). "Effects of Calcite and Dolomite Mining on Water and Soil Qualities: A case study of Freedom Group of Companies, Ikpeshi, Edo State Nigeria".Journal of Emerging Trends in Engineering and Applied Sciences.3(1): 19–24.
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