Phyllosilicate clays

1. Phyllosilicate Clay Minerals Structure and Properties Presented by Leah Brueggeman

2. C ommon Experiences w ith C lays Slippery Poorly drained Crack when dry Hard to dig M oldable

3. Soil fractions

4. Clay Characteristics Small particle size (clay size fraction) less than 002mm (2 microns) Large surface area (range from 10m 2 /g to 800m 2 /g) Carry a negative charge

5. Phyllosilicate Structure Phyllon – meaning leaf, Silic meaning flint Basic building blocks are Silicate Tetrahedron Aluminum Octahedron Basal oxygens Apical oxygen

6. Clay Structure Basal oxygens Apical oxygens Makes one layer

7. Two Layer Types 1:1 one tetrahedral: one octahedral 2:1 two tetrahedral : one octahedral Apical oxygen Apical oxygen Basal oxygen

8. Molecular and Structural

9. Origin Fluid and Rock Interaction Alteration Or Decomposition Weathering is a continual Process

10. Isomorphic Substitution Ions substitution in the basic mineral structure Al 3+ for Si 4+ in T etrahedral layer Fe 2+ , Fe 3+ , Mn 2+ , Mg 2+ for Al 3+ in Octahedral layer Results in charge imbalance (permanent charge) Isomorphic “same shape” refers to the substitution o f one ion for another without changing the morphology or structure of the mineral

11. Isomorphic Substitution 4 + 4 + 3+ 3+

12. Clay Types The type and amount of substitution creates clay minerals with different properties Properties affected include stickiness , plasticity, swelling, and cation exchange capacity 2:1 clay minerals fine grained micas, smectites and vermiculites,chlorites 1:1 clay minerals kaolinite

13. Smectite Vs. Kaolinite

14. Kaolinite Layers are electrically neutral because there is little cation substition in the structure Layers are held together by hydrogen bonds ( N on Expansive ) Charges are unsatisfied only on broken edges and surface (pH dependent) H + bonds

15. S mectite

16. Cation Exchange Capacity 1:1 Kaolinite Clay 2:1 Smectite clay At least as 20x greater CEC Non pH dependent because structural pH Dependent AEC Low CEC No Interlayer

17. Role in Importance to Ag Nutrient Retention Many plant nutrients are cations ( Ca , Mg, K,Na,H ) Water Holding Capacity : opposite charged end of the polar water molecule attracted to the internal and external surfaces CEC Soils with high CEC hold and retain important plant nutrients

18. Other actions of clay in soil Retention of contaminants Sorption of metals Soil Structure

19. Swelling Clay in ND

20. Hydrated Interlayer Shrinks and swells Can expand up to 30% Most Surface Area

21. Sodic Soils in ND

22. Dispersion Increasing Na + in solution Na + Na + Na + Need twice as many Na + than Ca 2+ Ca 2+ Ca 2+ Ca 2+

23. Slippery, Swells, Shrinks, Hard BUT Holds Water, Retains Nutrients Structure, Reduces Contaminants