Download - Phyllosilicate clays
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Phyllosilicate Clay Minerals
Structure and PropertiesPresented by Leah Brueggeman
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Common Experiences with Clays
– Slippery–Poorly drained–Crack when dry–Hard to dig–Moldable
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Soil fractions
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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
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Phyllosilicate Structure
– Phyllon – meaning leaf, Silic meaning flint– Basic building blocks are
Silicate Tetrahedron Aluminum Octahedron
Basal oxygens
Apical oxygen
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Clay Structure
Basal oxygens
Apical oxygens
Makes one layer
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Two Layer Types• 1:1 one tetrahedral:
one octahedral• 2:1 two tetrahedral:
one octahedral
Apical oxygen
Apical oxygen
Basal oxygen
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Molecular and Structural
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Origin
Fluid and Rock Interaction
Alteration Or Decomposition
Weathering is a continual Process
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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
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Isomorphic Substitution
4+
4+
3+
3+
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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 smectites, vermiculites, chlorites
• 1:1 clay mineralskaolinite
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Smectite Vs. Kaolinite
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Cation Exchange Capacity
1:1 Kaolinite ClayLow CEC No InterlayerNo isomorphic substitution
2:1 Smectite clayAt least 20x greater CECHydrated interlayer
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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
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Swelling Clay in ND
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Hydrated Interlayer
• Shrinks and swells
• Can expand up to 30%
• Most Surface Area
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Sodic Soils in ND
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DispersionIncreasing Na+ in solution
Na+
Na+Na+
Need twice as many Na+ than Ca2+
Ca2+
Ca2+
Ca2+
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