1. 1 Duration = 15 mins.

2. SIVA Copyright©2001 2 Elements of Earth 12500 km dia 8-35 km crust % by weight in crust O= 49.2 Si= 25.7 Al= 7.5 Fe= 4.7 Ca= 3.4 Na= 2.6 K= 2.4 Mg= 1.9 other= 2.6 82.4%

3. SIVA Copyright©2001 3 Soil Formation Parent Rock Residual soil Transported soil ~ in situ weathering (by physical & chemical agents) of parent rock ~ weathered and transported far away by wind, water and ice.

4. SIVA Copyright©2001 Parent Rock ~ formed by one of these three different processes igneous sedimentary metamorphic formed by cooling of molten magma (lava) formed by gradual deposition, and in layers formed by alteration of igneous & sedimentary rocks by pressure/temperature e.g., limestone, shale e.g., marble e.g., granite

5. SIVA Copyright©2001 5 Residual Soils Formed by in situ weathering of parent rock

6. SIVA Copyright©2001 6 Transported Soils Transported by:Special name:  wind“Aeolian”  sea (salt water)“Marine”  lake (fresh water)“Lacustrine”  river “Alluvial”  ice“Glacial”

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8. SIVA Copyright©2001 8 Basic Structural Units 0.26 nm oxygen silicon 0.29 nm aluminium or magnesium hydroxyl or oxygen Clay minerals are made of two distinct structural units. Silicon tetrahedronAluminium Octahedron

9. SIVA Copyright©2001 9 Tetrahedral Sheet Several tetrahedrons joined together form a tetrahedral sheet. tetrahedron hexagonal hole

10. SIVA Copyright©2001 10 Tetrahedral & Octahedral Sheets For simplicity, let’s represent silica tetrahedral sheet by: Si and alumina octahedral sheet by: Al

11. SIVA Copyright©2001 11 Different Clay Minerals Different combinations of tetrahedral and octahedral sheets form different clay minerals: 1:1 Clay Mineral (e.g., kaolinite, halloysite):

12. SIVA Copyright©2001 12 Different Clay Minerals Different combinations of tetrahedral and octahedral sheets form different clay minerals: 2:1 Clay Mineral (e.g., montmorillonite, illite)

13. SIVA Copyright©2001 Kaolinite Si Al Si Al Si Al Si Al joined by strong H-bond  no easy separation 0.72 nm Typically 70-100 layers joined by oxygen sharing

14. SIVA Copyright©2001 14 Kaolinite  used in paints, paper and in pottery and pharmaceutical industries Halloysite  kaolinite family; hydrated and tubular structure  (OH) 8 Al 4 Si 4 O 10.4H 2 O  (OH) 8 Al 4 Si 4 O 10

15. SIVA Copyright©2001 15 Montmorillonite Si Al Si Al Si Al Si 0.96 nm joined by weak van der Waal’s bond  easily separated by water  also called smectite; expands on contact with water

16. SIVA Copyright©2001 16 Montmorillonite  A highly reactive (expansive) clay  montmorillonite family  used as drilling mud, in slurry trench walls, stopping leaks  (OH) 4 Al 4 Si 8 O 20.nH 2 O high affinity to water Bentonite swells on contact with water

17. SIVA Copyright©2001 17 Illite Si Al Si Al Si Al Si 0.96 nm joined by K + ions fit into the hexagonal holes in Si-sheet

18. SIVA Copyright©2001 18 Others…  A 2:1:1 (???) mineral.  montmorillonite family; 2 interlayers of water  chain structure (no sheets); needle-like appearance Chlorite Vermiculite Attapulgite Si Al Al or Mg

19. SIVA Copyright©2001 19 A Clay Particle Plate-like or Flaky Shape

20. SIVA Copyright©2001 20 Clay Fabric Flocculated Dispersed edge-to-face contact face-to-face contact

21. SIVA Copyright©2001 21 Clay Fabric  Electrochemical environment (i.e., pH, acidity, temperature, cations present in the water) during the time of sedimentation influence clay fabric significantly.  Clay particles tend to align perpendicular to the load applied on them.

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23. SIVA Copyright©2001 23 Scanning Electron Microscope  common technique to see clay particles plate-like structure  qualitative

24. SIVA Copyright©2001 24 Others… X-Ray Diffraction (XRD) Differential Thermal Analysis (DTA)  to identify the molecular structure and minerals present  to identify the minerals present

25. SIVA Copyright©2001 25 Casagrande’s PI-LL Chart montmorillonite illite kaolinite chlorite halloysite

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27. SIVA Copyright©2001 27 Specific Surface  surface area per unit mass (m 2 /g)  smaller the grain, higher the specific surface e.g., soil grain with specific gravity of 2.7 10 mm cube 1 mm cube spec. surface = 222.2 mm 2 /gspec. surface = 2222.2 mm 2 /g

28. SIVA Copyright©2001 28 Isomorphous Substitution  substitution of Si 4+ and Al 3+ by other lower valence (e.g., Mg 2+ ) cations  results in charge imbalance (net negative) + + + ++ + + _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ positively charged edges negatively charged faces Clay Particle with Net negative Charge

29. SIVA Copyright©2001 29 Cation Exchange Capacity (c.e.c)  capacity to attract cations from the water (i.e., measure of the net negative charge of the clay particle)  measured in meq/100g (net negative charge per 100 g of clay) milliequivalents known as exchangeable cations  The replacement power is greater for higher valence and larger cations. Al 3+ > Ca 2+ > Mg 2+ >> NH 4 + > K + > H + > Na + > Li +

30. SIVA Copyright©2001 30 A Comparison MineralSpecific surface (m 2 /g) C.E.C (meq/100g) Kaolinite10-203-10 Illite80-10020-30 Montmorillonite80080-120 Chlorite8020-30

31. SIVA Copyright©2001 31 Cation Concentration in Water + ++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + cations  cation concentration drops with distance from clay particle - - - - - - - clay particle double layer free water

32. SIVA Copyright©2001 32 Adsorbed Water - - - - - - -  A thin layer of water tightly held to particle; like a skin  1-4 molecules of water (1 nm) thick  more viscous than free water adsorbed water

33. SIVA Copyright©2001 33 Clay Particle in Water - - - - - - - free water double layer water adsorbed water 50 nm 1nm

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35. SIVA Copyright©2001 35 Summary - Clays  Clay particles are like plates or needles. They are negatively charged.  Clays are plastic; Silts, sands and gravels are non-plastic.  Clays exhibit high dry strength and slow dilatancy.

36. SIVA Copyright©2001 36 Summary - Montmorillonite  Montmorillonites have very high specific surface, cation exchange capacity, and affinity to water. They form reactive clays.  Bentonite (a form of Montmorillonite) is frequently used as drilling mud.  Montmorillonites have very high liquid limit (100+), plasticity index and activity (1-7).