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{{Short description|Group of non-expanding clay minerals}}
⚫ ]
{{Infobox mineral
⚫ '''Illite''' is a non-expanding, ]-sized, micaceous mineral. Illite is a ] or layered alumino-silicate. Its structure is constituted by the repetition of Tetrahedron – Octahedron – Tetrahedron (TOT) layer. The interlayer space is mainly occupied by poorly hydrated potassium cations responsible for the absence of swelling. Structurally illite is quite similar to ] or ] with slightly more ], ], ], and water and slightly less tetrahedral ] and interlayer ]. The chemical formula is given as (K,H<sub>3</sub>O)(Al,Mg,Fe)<sub>2</sub>(Si,Al)<sub>4</sub>O<sub>10</sub><ref></ref>, but there is considerable ion substitution. It occurs as aggregates of small ] grey to white crystals. Due to the small size, positive identification usually requires ] analysis. Illite occurs as an alteration product of muscovite and ] in ] and ] environments. It is common is sediments, soils, and argillaceous ] as well as in some low grade ]. ] in sediments can be differentiated by x-ray analysis.
| name = Illite
| category = ]- ]
| boxwidth =
| boxbgcolor =
| image = Illite.jpg
| imagesize = 260px
| alt =
| caption =
| formula = {{Chem2|(K,H3O)(Al,Mg,Fe)2(Si,Al)4O10}}
| IMAsymbol = Ilt<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight =
| strunz = 9.EC.60
| dana = 71.02.02d.02
| system = ]
| class = Prismatic (2/m) <br/><small>(same ])</small>
| symmetry = ''C2/m'' (no. 12)
| color = Grey-white to silvery-white, greenish-gray
| colour =
| habit = Micaceous aggregates
| twinning =
| cleavage = {001} Perfect
| fracture =
| tenacity =
| mohs = 1–2
| luster = Pearly to dull
| streak = white
| diaphaneity = Translucent
| gravity = 2.6–2.9
| density =
| polish =
| opticalprop = Biaxial (−)
| refractive = nα = 1.535 – 1.570 nβ = 1.555 – 1.600 nγ = 1.565 – 1.605
| birefringence =
| pleochroism =
| 2V =
| dispersion =
| extinction =
| length fast/slow =
| fluorescence=
| absorption =
| melt =
| fusibility =
| diagnostic =
| solubility =
| other =
| alteration =
| references = <ref name=Mindat/><ref name=Webmin/><ref>{{cite journal |last1=Drits |first1=V. A. |last2=Zviagina |first2=B. B. |last3=McCarty |first3=D. K. |last4=Salyn |first4=A. L. |title=Factors responsible for crystal-chemical variations in the solid solutions from illite to aluminoceladonite and from glauconite to celadonite |journal=American Mineralogist |date=1 February 2010 |volume=95 |issue=2–3 |pages=348–361 |doi=10.2138/am.2010.3300|bibcode=2010AmMin..95..348D |s2cid=62881038 }}</ref>}}
⚫ ]


⚫ '''Illite''', also called '''hydromica''' or '''hydromuscovite''',<ref>{{Cite web|url=http://www.mindat.org/min-9603.html|title=Hydromuscovite: Mineral information, data and localities|website=www.mindat.org|access-date= 2023-08-27}}</ref> is a group of closely related non-expanding ] minerals. Illite is a secondary mineral precipitate, and an example of a ], or layered alumino-silicate. Its structure is a 2:1 sandwich of silica tetrahedron (T) – ] octahedron (O) – silica tetrahedron (T) layers.<ref name="USGS">{{Cite web|url=https://pubs.usgs.gov/of/2001/of01-041/htmldocs/clays/illite.htm|title=USGS OFR01-041: Illite Group Minerals|website=] Coastal and Marine Geology Program|access-date=3 Apr 2019}}</ref> The space between this T-O-T sequence of layers is occupied by poorly hydrated potassium cations which are responsible for the absence of swelling. Structurally, illite is quite similar to ] with slightly more ], ], ], and water and slightly less tetrahedral ] and interlayer ]. The chemical formula is given as {{Chem2|(K,H3O)(Al,Mg,Fe)2(Si,Al)4O10}},<ref name="Webmin">{{Cite web|url=http://webmineral.com/data/Illite.shtml|title=Illite Mineral Data|website=webmineral.com|access-date=3 Apr 2019}}</ref> but there is considerable ion (isomorphic) substitution. It occurs as aggregates of small ] grey to white crystals. Due to the small size, positive identification usually requires ] or SEM-EDS (]) analysis. Illite occurs as an altered product of muscovite and ] in ] and ] environments; it may be a component of ]. It is common in sediments, soils, and argillaceous ] as well as in some low grade ]. The iron-rich member of the illite group, ], in sediments can be differentiated by x-ray analysis.<ref>{{Cite journal|url=https://books.google.com/books?id=KhAJAQAAIAAJ|title=Crystal Structures of Clay Minerals and Their X-ray Identification|vauthors=Brindley GW, Brown G|journal=Mineralogical Society Monograph|publisher=Mineralogical Society|year=1980|edition=3rd|location=UK|isbn=9780903056083|issn=0144-1485}}</ref>
⚫ The cation exchange capacity (CEC) of illite is smaller than that of ] but higher than that of ], typically around 20 – 30 meq/100 g.


⚫ The ] (CEC) of illite is smaller than that of ] but higher than that of ], typically around 20 – 30 meq/100 g.
⚫ Illite was first described for occurrences in the Maquoketa ] in ], USA, in 1937. The name was derived from its type location in Illinois. Illite is also called hydromica or hydromuscovite. ] is a sodium rich analogue.


⚫ Illite was first described for occurrences in the Maquoketa ] in ], US, in 1937. The name was derived from its type location in Illinois.<ref name="Mindat">{{Cite web|url=http://www.mindat.org/min-2011.html|title=Illite: Mineral information, data and localities|website=www.mindat.org|access-date=3 Apr 2019}}</ref>
Illite is also used in '''food supplements''', with claimed benefits that range from bowel function to reduction of ] in the blood. Apparently, a French company, Argiletz, provides a wide range of products which are offered for sale in the ] and elsewhere. "Green clay", a term used in several languages, often contains illite. In ], internal uses of illite probably date back to ] times.

] is a sodium rich analogue. Avalite is a ] bearing variety which has been described from ], ], ].<ref>{{Cite web|url=https://www.mindat.org/min-435.html|title=Avalite: Mineral information, data and localities|website=www.mindat.org|access-date=3 Apr 2019}}</ref>

Zipao 'jade' is an ornamental form of illite showing bands of red-purple and pale yellow-green. It may be carved into pendants and other ornaments.

==Illite crystallinity==
{{main|Illite crystallinity}}
The crystallinity of illite has been used as an indicator of metamorphic grade in clay-bearing rocks metamorphosed under conditions between ] and low-grade metamorphism.<ref name="FreyRobinson1999">{{cite book|url=https://books.google.com/books?id=n4Sxrlq1g58C&pg=PA61|title=Low-Grade Metamorphism|vauthors=Frey M, Robinson D|publisher=Wiley|year=1999|isbn=9780632047567|pages=61–107}}</ref> With increasing temperature, illite is thought to undergo a transformation into ].<ref>{{Cite journal|vauthors=Gharrabi M, Velde B, Sagon JP|date=1998|title=The Transformation of Illite to Muscovite in Pelitic Rocks: Constraints from X-ray Diffraction|journal=Clays and Clay Minerals|volume=46|issue=1|pages=79–88|doi=10.1346/CCMN.1998.0460109|bibcode=1998CCM....46...79G|doi-access=}}</ref>


==References== ==References==
* Fundamentals of soil behavior. Second edition. John Wiley and Sons, Inc., New York. 437 pp, see Chapter 3, Soil Mineralogy, p. 32. *{{Cite book|title=Fundamentals of soil behavior|vauthors=Mitchell JK|publisher=John Wiley and Sons, Inc.|year=1993|isbn=9780471463023|edition=2nd|location=New York|pages=32|chapter=Ch. 3: Soil Mineralogy}}
{{reflist}} {{Reflist}}


==External links== ==External links==
*{{Commons category-inline}}
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{{Phyllosilicates}}
{{Clay minerals}}


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Latest revision as of 21:40, 3 August 2024

Group of non-expanding clay minerals
Illite
General
CategoryMica- phyllosilicates
Formula
(repeating unit)		(K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)]
IMA symbolIlt
Strunz classification9.EC.60
Dana classification71.02.02d.02
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m (no. 12)
Identification
ColorGrey-white to silvery-white, greenish-gray
Crystal habitMicaceous aggregates
Cleavage{001} Perfect
Mohs scale hardness1–2
LusterPearly to dull
Streakwhite
DiaphaneityTranslucent
Specific gravity2.6–2.9
Optical propertiesBiaxial (−)
Refractive indexnα = 1.535 – 1.570 nβ = 1.555 – 1.600 nγ = 1.565 – 1.605
References
Structure of illite mica – USGS

Illite, also called hydromica or hydromuscovite, is a group of closely related non-expanding clay minerals. Illite is a secondary mineral precipitate, and an example of a phyllosilicate, or layered alumino-silicate. Its structure is a 2:1 sandwich of silica tetrahedron (T) – alumina octahedron (O) – silica tetrahedron (T) layers. The space between this T-O-T sequence of layers is occupied by poorly hydrated potassium cations which are responsible for the absence of swelling. Structurally, illite is quite similar to muscovite with slightly more silicon, magnesium, iron, and water and slightly less tetrahedral aluminium and interlayer potassium. The chemical formula is given as (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2·(H2O)], but there is considerable ion (isomorphic) substitution. It occurs as aggregates of small monoclinic grey to white crystals. Due to the small size, positive identification usually requires x-ray diffraction or SEM-EDS (automated mineralogy) analysis. Illite occurs as an altered product of muscovite and feldspar in weathering and hydrothermal environments; it may be a component of sericite. It is common in sediments, soils, and argillaceous sedimentary rocks as well as in some low grade metamorphic rocks. The iron-rich member of the illite group, glauconite, in sediments can be differentiated by x-ray analysis.

The cation-exchange capacity (CEC) of illite is smaller than that of smectite but higher than that of kaolinite, typically around 20 – 30 meq/100 g.

Illite was first described for occurrences in the Maquoketa shale in Calhoun County, Illinois, US, in 1937. The name was derived from its type location in Illinois.

Brammallite is a sodium rich analogue. Avalite is a chromium bearing variety which has been described from Mt. Avala, Belgrade, Serbia.

Zipao 'jade' is an ornamental form of illite showing bands of red-purple and pale yellow-green. It may be carved into pendants and other ornaments.

Illite crystallinity

Main article: Illite crystallinity

The crystallinity of illite has been used as an indicator of metamorphic grade in clay-bearing rocks metamorphosed under conditions between diagenesis and low-grade metamorphism. With increasing temperature, illite is thought to undergo a transformation into muscovite.

References

  • Mitchell JK (1993). "Ch. 3: Soil Mineralogy". Fundamentals of soil behavior (2nd ed.). New York: John Wiley and Sons, Inc. p. 32. ISBN 9780471463023.
  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. ^ "Illite: Mineral information, data and localities". www.mindat.org. Retrieved 3 Apr 2019.
  3. ^ "Illite Mineral Data". webmineral.com. Retrieved 3 Apr 2019.
  4. Drits, V. A.; Zviagina, B. B.; McCarty, D. K.; Salyn, A. L. (1 February 2010). "Factors responsible for crystal-chemical variations in the solid solutions from illite to aluminoceladonite and from glauconite to celadonite". American Mineralogist. 95 (2–3): 348–361. Bibcode:2010AmMin..95..348D. doi:10.2138/am.2010.3300. S2CID 62881038.
  5. ^ "USGS OFR01-041: Illite Group Minerals". USGS Coastal and Marine Geology Program. Retrieved 3 Apr 2019.
  6. "Hydromuscovite: Mineral information, data and localities". www.mindat.org. Retrieved 2023-08-27.
  7. Brindley GW, Brown G (1980). "Crystal Structures of Clay Minerals and Their X-ray Identification". Mineralogical Society Monograph (3rd ed.). UK: Mineralogical Society. ISBN 9780903056083. ISSN 0144-1485.
  8. "Avalite: Mineral information, data and localities". www.mindat.org. Retrieved 3 Apr 2019.
  9. Frey M, Robinson D (1999). Low-Grade Metamorphism. Wiley. pp. 61–107. ISBN 9780632047567.
  10. Gharrabi M, Velde B, Sagon JP (1998). "The Transformation of Illite to Muscovite in Pelitic Rocks: Constraints from X-ray Diffraction". Clays and Clay Minerals. 46 (1): 79–88. Bibcode:1998CCM....46...79G. doi:10.1346/CCMN.1998.0460109.

External links

  • Media related to Illite at Wikimedia Commons
Phyllosilicates
Micas
Talcs
Pyrophyllite series
Kaolinites
Serpentines
Corrensites
Smectites and vermiculite family
Chlorites
Allophanes
Sepiolites
Pyrosmalites
Stilpnomelanes
  • Structural groups mainly; based on rruff.info/ima, modified
  • Minerals portal
Clay minerals
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