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

2. Common Experiences with Clays
–Slippery
–Poorly drained
–Crack when dry
–Hard to dig
–Moldable

3. Soil fractions

4. Clay Characteristics
• Small particle size (clay
size fraction) less than
002mm (2 microns)
• Large surface area
(range from 10m2/g to
800m2/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
– Al3+ for Si4+ in Tetrahedral layer
– Fe2+ , Fe3+, Mn2+ , Mg2+ for Al3+ in Octahedral layer
Results in charge imbalance (permanent charge)
Isomorphic “same shape” refers to the substitution
of 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

14. Smectite Vs. Kaolinite

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

16. Smectite

17. 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

18. 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

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

20. Swelling Clay in ND

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

22. Sodic Soils in ND

23. Dispersion
Increasing Na+ in solution
Na+
Na+Na+
Need twice as many Na+ than Ca2+
Ca2+
Ca2+
Ca2+

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