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Chapter 2 continued

Chapter 2 continued. 2:1 phyllosilicates Vermiculite, Mica, and Illite. 2 Tetrahedral sheets. + 1 octahedral sheet. http://pubpages.unh.edu/~harter/crystal.htm#2:1%20MINERALS. Form 2:1 minerals. www.geoclassroom.com/mineralogy/silicatelayer.gif.

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Chapter 2 continued

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  1. Chapter 2 continued 2:1 phyllosilicates Vermiculite, Mica, and Illite

  2. 2 Tetrahedral sheets + 1 octahedral sheet http://pubpages.unh.edu/~harter/crystal.htm#2:1%20MINERALS

  3. Form 2:1 minerals

  4. www.geoclassroom.com/mineralogy/silicatelayer.gif

  5. 2:1 Layer silicates with medium layer charge Vermiculite x = 1.2 – 1.8 • Dioctahedral vermiculite Mx,H2O [Si,Al]8[Al,Mg]4O20(OH)4 • Trioctahedral vermiculite Mx,H2O [Si,Al]8[Mg]6O20(OH)4 • The name vermiculite was created from the Latin word for worm, vermiculus. This is a reference to the fact that when vermiculite is heated, it expands into wormlike shapes.

  6. Vermiculite – common packing material and soil amendment http://www.duralite.com.au/images/Vermiculite_ore.jpg http://www.epa.gov/region8/sf/libby/abcasbestos.html

  7. http://grunwald.ifas.ufl.edu/Nat_resources/silicates/silicates.htmhttp://grunwald.ifas.ufl.edu/Nat_resources/silicates/silicates.htm

  8. http://pubs.usgs.gov/of/2001/of01-041/htmldocs/images/verstru.jpghttp://pubs.usgs.gov/of/2001/of01-041/htmldocs/images/verstru.jpg

  9. Medium-charge layer silicate properties • Variable layer charge • CEC = 10 - 200 cmol/kg (higher for tri- than dioctahedral) • High S.A. = 600-800 m2/g • Moderately Expansive (not as bad as smectites) • Non-plastic, non-sticky • C-spacing = 1.0-15 nm depending on treatment • K+ fixation

  10. Mica (L. micare, to shine) hand samples Oven windows, cosmetics, paints, …

  11. High-charge 2:1 mineralsMica x = 2 Dioctahedral: • Muscovite Kx[Si,Al]8 [Al4]O20(OH, F)4 • Paragonite Nax[Si,Al]8 [Al4]O20(OH, F)4 Trioctahedral: • Biotite Kx[Si,Al]8 [Mg, Fe, Al]6O20(OH, F)4 • Phlogopite Kx[Si,Al]8 [Mg6]O20(OH, F)4 • Lepidolite Kx[Si,Al]8 [Li,Al]6O20(OH, F)4

  12. High-charge 2:1 mineral properties • Source of K+ in soils as they weather • Non-expansive, non-sticky, non-plastic • S.A. = 70-120 m2/g (mostly external) • CEC = 10 - 40 cmol/kg • c-spacing = 1.0 nm • Interlayer held tightly together by K+ fit in ditrigonal cavities of tetrahedral sheet

  13. Mica structure http://www.geoclassroom.com/mineralogy/phyllosilicates.html

  14. http://pubs.usgs.gov/of/2001/of01-041/htmldocs/images/illstruc.jpghttp://pubs.usgs.gov/of/2001/of01-041/htmldocs/images/illstruc.jpg

  15. Illite • “Hydrous mica”, “micaceous clay”, weathered mica • Intermediate in formula and properties between mica and vermiculite or smectite CEC = 20-40 cmol/kg S.A. = 70-120 m2/g Fixed K+ • Term goes in and out of favor; used more by geologists & engineers than soil scientists

  16. http://pubs.usgs.gov/of/2001/of01-041/htmldocs/images/illstruc.jpghttp://pubs.usgs.gov/of/2001/of01-041/htmldocs/images/illstruc.jpg

  17. Hydrous Micas (Illites) • Illite is essentially a group name for non-expanding, clay-sized, dioctahedral, micaceous minerals. • Structurally similar to muscovite in that its basic unit is a layer composed of two inward-pointing silica tetragonal sheets with a central octahedral sheet. • 2 : 1 type minerals containing sufficient interlayer K+ to limit expansion on wetting. • The K+ content of hydrous mica is less than that of micas. • Charges not neutralized by K + are countered by hydrated cations. • Hydrous micas are widespread in soils. • The layer thickness of hydrous micas are about 1.0 nm.

  18. http://grunwald.ifas.ufl.edu/Nat_resources/silicates/illite.gifhttp://grunwald.ifas.ufl.edu/Nat_resources/silicates/illite.gif

  19. http://faculty.plattsburgh.edu/robert.fuller/370%20Files/Week6Mineralogy/Illite.htmhttp://faculty.plattsburgh.edu/robert.fuller/370%20Files/Week6Mineralogy/Illite.htm

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