Iceland spar
Iceland spar, formerly called Iceland crystal (Icelandic: silfurberg [ˈsɪlvʏrˌpɛrk], lit. 'silver-rock') and also called optical calcite, is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light.[1][2]
Formation and composition
Iceland spar is a colourless, transparent variety of calcium carbonate (CaCO3).[3] It crystallizes in the trigonal system, typically forming rhombohedral crystals.[4] It has a Mohs hardness of 3 and exhibits double refraction, splitting a ray of light into two rays that travel at different speeds and directions.[3][5]
Iceland spar forms in sedimentary environments, mainly limestone and dolomite rocks, but it also forms in hydrothermal veins and evaporite deposits.[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 in Iceland but can occur in different parts of the world with suitable geological conditions.[3][10]
Characteristics and optical properties
Iceland spar is characterized by its large, readily cleavable crystals, easily divided into parallelepipeds.[11][12] This feature makes it easily identifiable and workable. One of the most remarkable properties of Iceland spar is its birefringence, where the crystal's refractive index differs for light of different polarizations.[11][12] When a ray of unpolarized light passes through the crystal, it is divided into two rays of mutually perpendicular polarization 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 the plane of polarization of light passing through it, a property resulting from its asymmetrical atomic arrangement.[17] These optical properties contribute to the mineral's scientific use and aesthetic appeal.
Historical significance
Iceland spar holds historical importance in optics and the study of light.
The study of
The understanding of double refraction in Iceland spar also led to the development of polarized 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
Mines producing Iceland spar include many mines producing related calcite and aragonite. 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 greater Sonoran Desert region, in Santa Eulalia, Chihuahua, Mexico, and New Mexico, United States.[28][29][30] The clearest specimens, as well as the largest, have been from the Helgustaðir mine in Iceland.[31]
Surveying tools and techniques are combined to reduce the risk and cost of exploration to identify deposits.[32] Geological maps and remote sensing techniques, such as satellite imagery and aerial 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.
Environmental issues
Some potential environmental issues associated with Iceland spar mining include
Health concerns
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
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.
William Nicol (1770–1851) invented the first polarizing prism, using Iceland spar to create his Nicol prism.[51]
Modern applications
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 in cement and concrete. Its high purity and brightness make it an ideal filler in paints and coatings.[54] In metallurgy, calcite acts as a flux to lower the melting point of metals during smelting and refining.[55] Additionally, it is used in agriculture as a soil conditioner and 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
Due to Iceland spar typically forming in sedimentary environments, particularly limestone and dolomite rocks, its formation is closely tied to these carbonate rocks' deposition and
Conservation and protection
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 prevent overexploitation.[60]
Cultural impact
The Thomas Pynchon novel Against the Day uses the doubling effect of Iceland spar as a theme.[62]
See also
References
- ^ This article incorporates text from this source, which is in the public domain. Porter, Noah, ed. (1913). "Polarimetry". Webster's Dictionary. Springfield, Massachusetts: C. & G. Merriam Co.
- ^ "Iceland spar". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
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- ^ Hughes, H. Herbert., Iceland spar and optical fluorite: U. S. Bureau of Mines, Information Circular 6468 (1931)
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- ^ a b This article incorporates text from this source, which is in the public domain. Webster, Noah (1828). "Birefringence". Webster's Dictionary. Springfield, Massachusetts: C. & G. Merriam Co.
- ^ ISBN 1-177-85127-XChap. 6, p. 128.
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- ^ C. Huygens, Treatise on Light (Leiden: Van der Aa, 1690), translated by Silvanus P. Thompson, London: Macmillan, 1912, archive.org/details/treatiseonlight031310mbp; Project Gutenberg edition, 2005, gutenberg.org/ebooks/14725; Errata, 2016.
- ^ This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). "Isaac Newton". Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al.
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- ^ Huygens, Christiaan (1912). Treatise On Light. Osmania University, Digital Library Of India. Macmillan And Company., Limited.
- ^ Whittaker, E. T., A History of the Theories of Aether and Electricity. Dublin University Press, 1910.
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- ^ Russell, Daniel E . 17 February 2008. Retrieved December 31, 2010. "Helgustadir Iceland Spar Mine" mindat.org
- ^ 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"
- ^ Kelley, Vincent C. 1940. Retrieved December 31, 2010. "Iceland Spar in New Mexico". American Mineralogist, Volume 25, pp. 357-367
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- ^ "Helgustaðanáma". Umhverfisstofnun (in Icelandic). Retrieved 2020-08-20.
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- ^ a b 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.
- ^ 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.
- ^ a b Duffy, Lawrence (2015). "BCS 312: Land and Environments of the Circumpolar North II" (PDF). UArtic.
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- ^ Le Floch, A., Ropars, G., Lucas, J., Wright, S., Davenport, T., Corfield, M., & Harrisson, M. (2013). The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass?. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 469(2153), 20120651.
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- ^ "Pynchon's First Novel in 10 Years Has Sex, Explosives (Update1)". Bloomberg News. 2007-09-30. Archived from the original on 2007-09-30. Retrieved 2023-05-25.