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 = “same shape”

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

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) K 2 [(Si 6, Al 2 )] IV [Al 4 ] VI O 20 (OH) 4 (6 x Si 4+ ) + (6 x Al 3+ ) = 42+ (20 x O 2- ) +(4 x OH 1- ) = 44- 42 + + 44 - = -2 Net charge = -2 Satisfied by 2 x K 1+ ions that are “fixed” or tightly held in interlayer Pyrophyllite (no sub’n) [Si 8 ] IV [Al 4 ] VI O 20 (OH) 4 (8 x Si 4+ ) + (4 x Al 3+ ) = 44+ (20 x O 2- ) +(4 x OH 1- ) = 44- 44 + + 44 - = 0 Net charge = 0

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

8. 2:1 minerals with low layer charge (x) Smectitesx = 0.4 – 1.2 Dioctahedral Montmorillonite M x,H 2 O [Si 8 ][Al,Mg] 4 O 20 (OH) 4 Beidellite M x,H 2 O [Si,Al] 8 [Al 4 ]O 20 (OH) 4 Nontronite M x,H 2 O [Si,Al] 8 [Fe +3 ] 4 O 20 (OH) 4 Trioctahedral SaponiteM x,H 2 O [Si,Al] 8 [Mg 6 ]O 20 (OH) 4 HectoriteM x,H 2 O [Si 8 ][Mg,Li] 6 O 20 (OH) 4

9. http://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 m 2 /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 authigenic quartz crystals and smectite clay coating another mineral grain. http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=163 authigenicquartzsmectiteclaycoatingmineral

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