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
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
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
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
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
Add red scale arrow
https://growabundant.com/wp-content/themes/natural/lib/timthumb.php?src=http://growabundant.com/wp-content/uploads/2015/03/220px-Sand_under_electron_microscope.jpg&w=358&h=0&zc=1
http://www.azonano.com/images/Article_Images/ImageForArticle_3080(3).gif
http://bedecid.com/bedington-silt-loam-soil.html
Give an example of how small .002 mm is compared to a biological (bacteria) Image
Example of surface area e.g. football field
Keep these characteristics in mind as we discuss the structure
Tetrahedral sheet: two planes of oxygens with mainly Si in the spaces between the oxygens (four sided geometric solid interlocking array with each sharing its basal oxygens with the Si neighbor results in large sheets.
Octahedral sheet: six oxygen atoms around a centra Al or Mg atom forming an eight sided geometric solid (octahedron) they link together to form the octahedral sheet
It is variances in the planes, sheets and layers that vary between one clay mineral and another
Can be confusing but the important aspects of the layers are the way they are stacked
NOT just a smaller version of sand and silt fraction. Cant make clay by grinding sand and silt
http://download.e-bookshelf.de/download/0003/7612/78/L-X-0003761278-0002098135.XHTML/images/c01_image009.jpg
Although this seems like backtracking I’m actually leading up to the next step in clay structure which depends on the origin
Takes place during crystallization and not subject to change.
http://www.thedirtdoctors.com/wp-content/uploads/2015/03/Structure-of-clay.png
In this slide need to introduce the idea of differences in the sheet (isomorphic substitution) and how it makes such a difference in mineral layers
Compare and contrast to show how structure affects properties
Highligts the importance of interlayer and isomorphic substitution
----- Meeting Notes (7/1/15 16:32) -----
maybe dont talk about pH dependent or at least practice it better
Provides soils cohesion (structure), binding soil particles creates soil pore. Holds water through capillary action
So knowing that just 20% clay in a soil can dominate the soil and also that each phyllosilicate has unique propertiies makes it important to use the specific clay mineralogy of a soil to select the best management practices.