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Chapter 2 continued

Chapter 2 continued. 2:1 phyllosilicates. Isomorphous Substitution. Substitution, during formation , of one ion for another of similar SIZE (but not necessarily the same charge) in an ionic solid without changing the structure (shape, morphology) of the crystal. Isomorphic = “same shape”.

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Chapter 2 continued

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  1. Chapter 2 continued 2:1 phyllosilicates

  2. Isomorphous Substitution Substitution, during formation, of one ion for another of similar SIZE (but not necessarily the same charge) in an ionic solid without changing the structure (shape, morphology) of the crystal. Isomorphic = “sameshape”

  3. 2 Tetrahedral sheets + 1 octahedral sheet http://pubpages.unh.edu/~harter/crystal.htm#2:1%20MINERALS

  4. Form 2:1 minerals

  5. Oreo cookies serve as models for layer minerals (phyllosilicates) One Oreo can be a mica or smectite-type mineral First proposed by Jerry Irvin at UCR

  6. Muscovite (Tet’l sub’n) K2[(Si6, Al2)]IV[Al4]VIO20(OH)4 (6 x Si4+) + (6 x Al3+) = 42+ (20 x O2-) +(4 x OH1-) = 44- 42+ + 44- = -2 Net charge = -2 Satisfied by 2 x K1+ ions that are “fixed” or tightly held in interlayer Pyrophyllite (no sub’n) [Si8]IV[Al4]VIO20(OH)4 (8 x Si4+) + (4 x Al3+) = 44+ (20 x O2-) +(4 x OH1-) = 44- 44+ + 44- = 0 Net charge = 0

  7. Muscovite Pyrophyllite http://www.a-m.de/images/pyrophyllit_01gre.jpg

  8. 2:1 minerals with low layer charge (x) Smectites x = 0.4 – 1.2 Dioctahedral Montmorillonite Mx,H2O [Si8][Al,Mg]4O20(OH)4 Beidellite Mx,H2O [Si,Al]8[Al4]O20(OH)4 Nontronite Mx,H2O [Si,Al]8[Fe+3]4O20(OH)4 Trioctahedral Saponite Mx,H2O [Si,Al]8[Mg6]O20(OH)4 Hectorite Mx,H2O [Si8][Mg,Li]6O20(OH)4

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

  10. Low-charge smectite properties • Shrink-swell characteristics • Plastic • High S.A. (both external + internal or interlayer area) = 600-800 m2/g • High CEC; 80-150 cmol/kg • Expansive - c-spacing variable with cation saturation and heat (1.0 –2.0 nm) • Very small particles (fine clay) • Flakey shape (e.g., corn flakes)

  11. Authigenic smectite (montmorillonite) overgrown on pore spaces and authigenicly-overgrown quartz grains in a sandstone. http://webmineral.com/specimens/picshow.php?id=1285

  12. Quartz. This SEM (scanning electron microscope) photograph shows authigenicquartz crystals and smectiteclaycoating another mineral grain.http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=163

  13. Montmorillonite www-esd.lbl.gov/sposito/ figure created by Dr. Sung-Ho Park

  14. surface cracks in Vertisol (Utah) soils.ag.uidaho.edu/soilorders/i/Vert_07b.jpg

  15. Damage to buildings on Vertisols soils.ag.uidaho.edu/soilorders/vertisols_07.htm

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