Cordierite


Cordierite
Cordierite

Cordierite from Italy
General
Category Silicate mineral
Chemical formula (Mg,Fe)2Al4Si5O18
Strunz classification 09.CJ.10
Dana classification 61.02.01.01 Cordierite group
Crystal symmetry 2/m 2/m 2/m Orthorhombic - Dipyramidal
Unit cell a = 17.079 Å, b = 9.730 Å, c = 9.356 Å; Z = 4
Identification
Color Blue, smoky blue, bluish violet; greenish, yellowish brown, gray; colorless to very pale blue in thin section
Crystal habit Pseudo-hexagonal prismatic twins, as imbedded grains, and massive
Crystal system Orthorhombic - Dipyramidal Space Group: C ccm
Twinning Common on {110}, {130}, simple, lamellar, cyclical
Cleavage Fair on {100}, poor on {001} and {010}
Fracture Subconchoidal
Tenacity Brittle
Mohs scale hardness 7 - 7.5
Luster Greasy or vitreous
Streak White
Specific gravity 2.57 - 2.66
Optical properties Usually optically (-), sometimes (+); 2V = 0-90°
Refractive index nα = 1.527 - 1.560 nβ = 1.532 - 1.574 nγ = 1.538 - 1.578 Indices increase with Fe content.
Pleochroism X = pale yellow, green; Y = violet, blue-violet; Z = pale blue
Fusibility on thin edges
Diagnostic features Resembles quartz can be distinguished by pleochroism. Can be distinguished from corundum by its lower hardness
References [1][2][3][4]

Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18).[2] A high temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.[3]

Crystal structure of Cordierite

         

Contents

Name and discovery

Cordierite, which was discovered in 1813, is named after the French geologist Louis Cordier (1777–1861).[2]

Occurrence

Cordierite typically occurs in contact or regional metamorphism of argillaceous rocks. It is especially common in hornfels produced by contact metamorphism of pelitic rocks. Two common metamorphic mineral assemblages include sillimanite-cordierite-spinel and cordierite-spinel-plagioclase-orthopyroxene. Other associated minerals include garnet (cordierite-garnet-sillimanite gneisses) and anthophyllite.[4][5] Cordierite also occurs in some granites, pegmatites, and norites in gabbroic magmas. Alteration products include mica, chlorite, and talc. Cordierite occurs in the granite contact zone at Geevor Tin Mine in Cornwall.

Commercial use

Catalytic converters are commonly made from ceramics containing a large proportion of cordierite. The manufacturing process deliberately aligns the cordierite crystals to make use of the very low thermal expansion seen for one axis. This prevents thermal shock cracking from taking place when the catalytic converter is used.[6]

Gem variety

As the transparent variety iolite, it is often used as a gemstone. The name "iolite" comes from the Greek word for violet. Another old name is dichroite, a Greek word meaning "two-colored rock", a reference to cordierite's strong pleochroism. It has also been called "water-sapphire" and "Vikings' Compass" because of its usefulness in determining the direction of the sun on overcast days, the Vikings having used it for this purpose[7]. This works by determining the direction of polarization of the sky overhead. Light scattered by air molecules is polarized, and the direction of the polarization is at right angles to a line to the sun, even when the sun's disk itself is obscured by dense fog or lies just below the horizon.[8]

Gem quality iolite varies in color from sapphire blue to blue violet to yellowish gray to light blue as the light angle changes. Iolite is sometimes used as an inexpensive substitute for sapphire. It is much softer than sapphires and is abundantly found in Sri Lanka, India, Burma, Australia's Northern Territory, Namibia, Brazil, Tanzania, Madagascar, Connecticut, and the Yellowknife area of the Northwest Territories of Canada.

Geologist Dan Hausel, University of Wyoming, found iolite deposits in Wyoming. These are some of the largest deposits in the world. One iolite that he recovered weighed in at more than 24,000 carats--the largest ever found in the world.[9]

See also

References

  1. ^ "Cordierite" (PDF). Handbook of Mineralogy. RRUFF™ Project. http://rruff.geo.arizona.edu/doclib/hom/cordierite.pdf. 
  2. ^ a b c "Cordierite". Mindat.org. http://www.mindat.org/min-1128.html. 
  3. ^ a b http://webmineral.com/data/Cordierite.shtml Webmineral data
  4. ^ a b Dana, James Dwight; Klein, Cornelis; Hurlbut, Cornelius S. (1985). Manual of Mineralogy (20th ed.). New York: John Wiley and Sons. pp. 395–396. ISBN 0-471-80580-7. 
  5. ^ Klein, Cornelis (2002). The Manual of Mineral Science (22nd ed.). John Wiley & Sons, Inc. ISBN 0-471-25177-1. 
  6. ^ Cybulski, Andrzej; Moulijn, Jacob A., eds (2005). Structured Catalysts and Reactors (Second ed.). CRC Press. pp. 35. ISBN 978-0824723439. 
  7. ^ Guillot, Agnès; Meyer, Jean-Arcady (2010) [Published in French in 2008]. How To Catch a Robot Rat: When Biology Inspires Innovation [La bionique: Quand la science imite la Nature]. Translated by Susan Emanuel. The MIT Press. p. 212. ISBN 978-0-262-01452-6. "Many insects and a few birds perceive polarized light. The Vikings used cordierite for this purpose, a stone that allowed them to reckon the position of the sun by observing the stone's changes in color." 
  8. ^ Noel, Oscar; Bowling, Sue Ann (March 21, 1988). "Polar Navigation and the Sky Compass". Alaska Science Forum. Geophysical Institute, University of Alaska Fairbanks. http://www.gi.alaska.edu/ScienceForum/ASF8/865.html. 
  9. ^ Topix Local News: Casper, WY, Wyoming is Most Gemstone-Rich State in US, Sept. 13, 2011

External links


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Look at other dictionaries:

  • Cordiérite — Cordiérite[1] Catégorie IX : silicates[2] …   Wikipédia en Français

  • Cordierite — Cordiérite Cordiérite Catégorie IX : silicates Cordiérite Généra …   Wikipédia en Français

  • CORDIÉRITE — Minéral auquel le géologue français Louis Cordier donna son nom, connu aussi sous les termes d’iolite (roche violette) ou de dichroïte (roche bicolore). Longtemps classée parmi les cyclosilicates, la cordiérite est classée parmi les… …   Encyclopédie Universelle

  • Cordierite — Cor di*er*ite (k[^o]r d[i^]*[ e]r*[imac]t), n. [Named after the geologist Cordier.] (Min.) See {Iolite}. [1913 Webster] …   The Collaborative International Dictionary of English

  • cordierite — [kôr′dē ər īt΄] n. [after P. L. A. Cordier (1777 1861), Fr geologist + ITE1] a bluish, very hard, pleochroic, crystalline mineral, magnesium aluminum silicate, (Mg,Fe) 2 Al4Si5O18, used sometimes as a gem …   English World dictionary

  • cordierite — /kawr dee euh ruyt /, n. a strongly dichroic blue mineral consisting of a silicate of magnesium, aluminum, and iron: common in metamorphic rocks. Also called dichroite, iolite. [1805 15; named after Pierre L. A. Cordier (1777 1861), French… …   Universalium

  • cordierite — kordieritas statusas T sritis chemija apibrėžtis Mineralas. formulė Mg₂Al₃[AlSi₅O₁₈] atitikmenys: angl. cordierite rus. кордиерит …   Chemijos terminų aiškinamasis žodynas

  • cordierite — noun Etymology: French, from Pierre L. A. Cordier died 1861 French geologist Date: circa 1814 a blue mineral of vitreous luster and strong dichroism that consists of a silicate of aluminum, iron, and magnesium …   New Collegiate Dictionary

  • cordierite — noun a magnesium iron aluminium cyclosilicate Syn: iolite …   Wiktionary

  • cordierite — cor·die·rì·te s.f. TS mineral. minerale rombico, costituente di alcune rocce metamorfiche, formato da silicato di magnesio e ferro, presente in vari colori tra cui l azzurro, che viene impiegato come sostitutivo meno pregiato dello zaffiro… …   Dizionario italiano