Structure of Illite mica - USGS.

Illite is a non-expanding, clay-sized, micaceous mineral. Illite is a phyllosilicate or layered slilcate. Structurally illite is quite similar to muscovite or sericite 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)][1] (http://webmineral.com/data/Illite.shtml), but there is considerable ion substitution. It occurs as aggregates of small monoclinic grey to white crystals. Due to the small size, positive identification usually requires x-ray diffraction analysis. Illite occurs as an alteration product of muscovite and feldspar in weathering and hydrothermal environments. It is common is sediments, soils, and argillaceous sedimentary rocks as well as in some low grade metamorphic rocks. Glauconite in sediments can be differentiated by x-ray analysis. Clay is a generic term for an aggregate of hydrous silicate particles less than 4 μm (micrometres) in diameter. ... The silicate minerals make up the the largest and most important class of rock-forming minerals. ... Muscovite layer Muscovite, also known as potash mica, is a phyllosilicate mineral of aluminium and potassium. ... General Name, Symbol, Number silicon, Si, 14 Series metalloid Group, Period, Block 14 (IVA), 3, p Density, Hardness 2330 kg/m3, 6. ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white Atomic mass 24. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metal Group, Period, Block 8 (VIIIB), 4, d Density, Hardness 7874 kg/m3, 4. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13 (IIIA), 3, p Density, Hardness 2700 kg/m3, 2. ... General Name, Symbol, Number potassium, K, 19 Series alkali metals Group, Period, Block 1(IA), 4, s Density, Hardness 856 kg/m3, 0. ... In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. ... X-ray crystallography is a technique in crystallography in which the pattern produced by the diffraction of x-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. ... Feldspar (from the German Feld, field, and Spat, a rock that does not contain ore) is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... Weathering is the process of decomposition and/or disintegration of rocks in situ, that is, in place. ... Hydrothermal circulation in the oceans is the passage of the water through mid-ocean Ridge (MOR) systems. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means change in form, derived from the Greek words meta, change, and morphe, form. The protolith is subjected to extreme heat (>150 degrees Celsius) and pressure causing profound... Glauconite is a phyllosilicate (mica group) mineral of formula: (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2. ...

Illite was first described for occurrences in the Maquoketa shale in Calhoun County, Illinois, USA, in 1937. The name was derived from its type location in Illinois. Illite is also called hydromica or hydromuscovite. Brammallite is a sodium rich analogue. Shale Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. ... Calhoun County is a county located in the state of Illinois. ...

References

• Webmineral (http://webmineral.com/data/Illite.shtml)
• USGS (http://pubs.usgs.gov/of/of01-041/htmldocs/clays/illite.htm)
• Mindat (http://www.mindat.org/min-2011.html)