phyllosilicate clays
TRANSCRIPT
Phyllosilicate Clay Minerals
Structure and PropertiesPresented by Leah Brueggeman
Common Experiences with Clays
– Slippery–Poorly drained–Crack when dry–Hard to dig–Moldable
Soil fractions
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
Phyllosilicate Structure
– Phyllon – meaning leaf, Silic meaning flint– Basic building blocks are
Silicate Tetrahedron Aluminum Octahedron
Basal oxygens
Apical oxygen
Clay Structure
Basal oxygens
Apical oxygens
Makes one layer
Two Layer Types• 1:1 one tetrahedral:
one octahedral• 2:1 two tetrahedral:
one octahedral
Apical oxygen
Apical oxygen
Basal oxygen
Molecular and Structural
Origin
Fluid and Rock Interaction
Alteration Or Decomposition
Weathering is a continual Process
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
Isomorphic Substitution
4+
4+
3+
3+
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 mineralskaolinite
Smectite Vs. Kaolinite
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
Smectite
Cation Exchange Capacity
1:1 Kaolinite Clay
2:1 Smectite clayAt least as 20x greater CECNon pH dependent because structural
pH Dependent AECLow CEC No Interlayer
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
Other actions of clay in soil
• Retention of contaminants• Sorption of metals• Soil Structure
Swelling Clay in ND
Hydrated Interlayer
• Shrinks and swells
• Can expand up to 30%
• Most Surface Area
Sodic Soils in ND
DispersionIncreasing Na+ in solution
Na+
Na+Na+
Need twice as many Na+ than Ca2+
Ca2+
Ca2+
Ca2+
Slippery, Swells, Shrinks, Hard
BUT
Holds Water, Retains NutrientsStructure, Reduces Contaminants