AGR 2320 Lecture Notes - Lecture 31: Ammonium Nitrate, Clay Minerals, Modelling Clay
16 Nov 2017
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Clays -AGR 2320 Thursday, November 16, 2017
• Building blocks of clay minerals: Silica tetrahedron, isomorphic
substitution (more negativity charged)
• Aluminum Octahedron: Mg replacing the Al, has a different charge,
therefore greater negative charge
• Silica tetrahedral sheet- every single O2 molecule is shared between two
Al
• Sometimes you see a side profile of the silica tetrahedron sheet
• Octahedral Sheet: OH group is shared between to Al, half negative on
each side(Al has 3 positive charges)
• Sheets of Si Tetrahedral and Al Octahedral joined by tetrahedral bonded
O replacing an octahedral bonded OH; 1:1 struct.
• Examples of a 1:1 clay struct. Kaolinite
• Kaolinite: one silica tetrahedral sheet to one Al octahedral sheet.
Negative charge on this clay mineral
• Two clay structs of Kaolinite
stacked on each other by
hydrogen bonding- even with
no charge there is still
polarity. Therefore, hydrogen
bonding can happen.
Hydrogen would likely be
located on top of oxygen, far
away from the Al molecule.
No charge in total the bottom
has polar negative and top
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2
has polar positive charge. Hydrogen bonding is very strong.
Kaolinite
• Very small amounts of surface area
• very little shrink swell potential
• used for modeling clay
• glued together by hydrogen bonding
Tetrahedral sheet on top and bottom of Octahedral sheet
• 2:1 struct clay
• Space in struct for potassium to fit or ammonium nitrate
• No ability for cations to move in and out of space
• Low shrink swell potential
• Intermediate surface area
• Relatively small amount of negative charge
• Hydrous mica (clay on steroids, smaller form of mica) Illite
• Low CEC
• Glued together with potassium in between, weathering can cause the
layer to separate, potassium will leave the space, any hydrated cation
will replace (hydrated radius)
• When they weather apart your removing a cation and replaced it with a
hydrated cation. The hydrated cations can move in and out of clay space.
These are called Vermiculite and Smecitite
• Vermiculite and Smecitite: Hydrated cations, high shrink swell potential,
high surface, a lot more net negative charge meaning it can hold on to a
lot more cations , cannot leach through profile very easily (CEC- cation
exchange capacity)
find more resources at oneclass.com
find more resources at oneclass.com
