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[il-ahyt] /ˈɪl aɪt/
any of a group of clay minerals, hydrous potassium aluminosilicates, characterized by a three-layer micalike structure and a gray, light green, or yellowish-brown color.
1937; ill(inois) + -ite1
Related forms
[ih-lit-ik] /ɪˈlɪt ɪk/ (Show IPA),
adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for illite
  • Dyna- illite only brought the remains of old shipwrecks to the surface.
  • Infiltration capacity seems to be influenced by the proportion of illite within the silt sized fraction.
British Dictionary definitions for illite


a clay mineral of the mica group, found in shales and mudstones. Crystal structure: monoclinic. Formula: K1–1.5Al4(Si6.5–7Al1–1.5O20)(OH)4
Word Origin
C20: named after Illinois, where it was first found
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Encyclopedia Article for illite

any of a group of mica-type clay minerals widely distributed in marine shales and related sediments. Illite contains more water and less potassium than true micas, but it has a micalike sheet structure and is poorly crystallized. It may form a chemical series with both muscovite and montmorillonite; it is a weathering product of muscovite and alters to montmorillonite under humid conditions. For chemical formula and detailed structure and physical properties, see clay mineral (table); mica (table)

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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