LECTURE 4:
CHEMICAL WEATHERING,
“CLAY” MINERALS, & SOILS
Coming Soon: List of potential
questions for Test 1 on 9 February
2005 and Earlier on Line for Example
Physical
Vs. Chemical
Fragmentation
Vs. Decay
(Geochemical &
Pedochemical)
Stability Series
Compare to
Bowen's Reaction Series
High-Temperature
Geochemical Equilibrium
1
High
Bowen’s Reaction Series
(for Silicate Minerals)
Olivine
Temperature
Ca Plagioclase
Pyroxene
Amphibole
Na Plagioclase
Biotite
Orthoclase
Low
Muscovite
Quartz
Most Important Igneous Rocks
Mineral Composition
Texture
Felsic
Intermediate Mafic
scoria
Cellular, pumice
obsidian
Glassy
Fine
Mix
rhyolite andesite basalt
rhyolite andesite basalt
UltraMafic
rare
rare
porphyry porphyry porphyry rare
Coarse granite diorite
peridotite
Olivine
Pyroxene
Amphibole
Ca Plag
Orthoclase
Quartz
Muscovite
Biotite Na Plag
Bowen’s Reaction Series &
Igneous Rock Classification
gabbro
Texture
Mineral Composition
Intermediate
Felsic
scoria
Cell, Glassy pumice obsidian
Fine
Mix
Coarse
Mafic
Ultra-Mafic
rare
rhyolite
andesite
basalt
rhyolite
basalt
porphyry
andesite
porphyry
porphyry
rare
granite
diorite
gabbro
peridotite
rare
2
High
Bowen’s Reaction Series
(for Silicate Minerals)
Olivine
Amphibole
Biotite
Na Plagioclase
Orthoclase
Low
Muscovite
Temperature
Ca Plagioclase
Pyroxene
Quartz
Unstable
Goldich (1938) Stability Series
(for Sand & Silt)
Olivine
Pyroxene
Amphibole
Biotite
Ca Plagioclase
Na Plagioclase
Stable
Orthoclase
Muscovite
Quartz
M.L. Jackson's Weathering Index (1968)
for Clay-size Particles (Partial List)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Gypsum, Halite, Anhydrite
Calcite, Apatite
Olivine, Pyroxene, Amphibole
Biotite, Glauconite
Albite, Anorthite, Obsidian
Quartz, Cristobalite
Muscovite, Sericite*
Vermiculite*
Smectite*
Kaolinite*
Gibbsite*
Hematite*, Goethite*
Rutile, Zircon
*=
Weathering Products
Leave Room
for all this!
Rock-forming Minerals Underlined
3
Jackson's Weathering Index
for Clay-Sized Particles
1.
2.
3.
4.
5.
6.
7.
Gypsum, Halite, Anhydrite
Calcite, Apatite
Olivine, Pyroxene, Amphibole
Biotite, Glauconite
Albite, Anorthite, Obsidian
Quartz, Cristobalite
Muscovite, Sericite*
Jackson's Weathering Index
for Clay-Sized Particles
8.
9.
10.
11.
12.
13.
Vermiculite*
Smectite*
Kaolinite*
Gibbsite*
Hematite*, Goethite*
Rutile, Zircon
* = Weathering Products
Rock-forming Minerals Underlined
No cell phone use in class or lab.
The American Geological Institute is pleased
to announce the 2007 William L. Fisher
Congressional Fellowship program and the
2007 Government Affairs Internship program
for students interested in working on Federallevel policy issues.
E-mail Drs. Kite or Wilson if interested.
4
Types of Chemical Weathering
Reactions (List, Cover)
1.
2.
3.
4.
5.
6.
7.
Solution
Oxidation-reduction
Carbonation
Hydration
Chelation
Ion Exchange
Hydrolysis
1. Solution
CaCO3 = Ca2+ (aq) + CO32- (aq)
Common-ion Effect:
e.g. Anhydrite: (Ca2+) Increases
in Solution
2. OXIDATION-REDUCTION
Fe+2 (Ferrous) = Fe+3 (Ferric) + Electron
Loss of Electron = Oxidation
(Not Always Lost to Oxygen)
Gain of Electron = Reduction
5
Eh = Redox Potential:
Ability of an Environment to
Yield or Absorb Electrons
Electron Volts:
+ Favors Oxidation
- Favors Reduction
Stability Fields of
Hematite and
Magnetite in Water
Source:
Garrels, Robert M., and Christ,
Charles L., 1965, Solution,
Minerals, and Equilibria: San
Francisco, Freeman, Cooper
& Company, 450 p.
Stability Fields of
Cu - Fe – S - O - H
System
Think About Complexity of
Real World with 92 Elements
Source:
Garrels, Robert M., and Christ,
Charles L., 1965, Solution,
Minerals, and Equilibria: San
Francisco, Freeman, Cooper
& Company, 450 p.
6
FeS2 = Pyrite
AMD =
Acid Mine Drainage
Dobbin, WV
Pyrite
Fe(OH)3(s) = “Yellow Boy”
Acid Mine Drainage Equations
From Renton, Stiller & Rymer (1989)
Pyrite
FeS2 + 3.5 O2 + H2O = Fe2+ + 2 SO42- + 2 H+
Fe2+ + 0.25 O2 + H+ = Fe3+ + 0.5 H2O
Fe3+ + 3 H2O
= Fe(OH)3(s) + 3 H+
FeS2 + 14 Fe3+ + 8 H2O =
15 Fe2+ + 2 SO42- + 16 H+
Fe2+ : Ferrous
Fe3+ : Ferric
FeS2 = Pyrite
Fe(OH)3(s) = “Yellow Boy”
3. CARBONATION
Native Cu Â
Malachite (CuCO3.Cu(OH)2)
or Azurite
http://www.minerals.net/
mineral/index.htm
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4. HYDRATION
Anhydrite → Gypsum
CaSO4 + 2 H2O = CaSO4 n 2 H2O
http://www.minerals.net/mineral/index.htm
5. CHELATION
Complex Organic Process
by Which Metallic Cations
Are Incorporated Into
Hydrocarbon Molecule
Chelation
Na+
Ca2+
K+
Mg2+
Fertile Cation-Rich Soil
8
Chelation
H+
Ca2+
K+
H+
H+
H+
H+
H+
Na+
Mg2+
Chelation
Cation
Exchange
Ca2+
K+
H+
H+
H+
H+
H+
H+
Na+
Mg2+
Chelation
Cations Taken
Into Plant
H+
H+
H+
Ca2+
Na+
H+
Mg2+
K+
H+
H+
9
Chelation
Cations
in the
Plant
H+
H+
H+
H+
Infertile Cation-Depleted Soil
H+
H+
Chelation
Oh
Shoot!
Ca
ti
on
Cations
Recycle
into Soil
s
H+
H+
H+
H+
H+
Infertile Cation-Depleted Soil
H+
6. IONIC EXCHANGE
Cations Substitute for Other Cations
in Crystal Lattice
Controlled by Ionic Radius, Soil
Particle Charges
Basic Environments:
Na < K < Mg < Ca
Easy Remove <-----> Held Tight
10
6. IONIC EXCHANGE
Acid Environment: H+, Al3+
Replace Other Cations
Base Saturation (%)=
# Exchangeable Base
X100%
# Exchangeable Bases + H
With Increased Leaching
-- BS Decreases
Decrease BS
-- Poor Agriculture Soil
Cation Exchange Capacity
Measures # of Potential
Cation Sites
Directly Related to Soil Mineralogy
– Not Easily Changed by Liming or
Fertilization
Slide Reinstituted after lecture in 2007
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7. HYDROLYSIS
salt + water = acid + base
2 KAlSi3O8 + 2 H2CO3 + 9 H2O =
Al2Si2O5(OH)4 + 4 H4SiO4 + 2 K+ + 2 HCO3-
In Extreme Weathering
(e.g. Tropics Over Long Time)
All Silica Leached Out
Al2Si2O5(OH)4 + 5 H2O = 2 Al(OH)3 + 2 H4SiO4
(Kaolinite)
(Gibbsite)
Clay Minerals:
Clay Has “Two” Meanings:
Textural:
Unified (Engineers):
< 5.00 µm
Wentworth (Geologists): < 3.96 µm
Soil Science:
< 2.00 µm
Mineralogical:
Hydrous Aluminous Phyllosilicates
Quartz-Clay Break Occurs ~ 2 µm
12
Clay Mineral Tour
Start With Simple and Get
More Complicated
Start With Most Stable &
Highest Alumina Content
Muscovite Mica (Sheet Silicate)
Gibbsite Al(OH)3
Not a True Clay (No Silica)
Building Block in Clays.
13
Al(OH)3 or Al Octahedron
OHAl
Two 4-sided Pyramids Stuck Together @ Base
Al3+ in Center, OH- at Nodes
Al(OH)3 Octahedra
Building Blocks in Clays.
1:1 Sheet Sillicate
Slides Marked with # Were Taken
In Part From This Web Site:
An Insiders Look at the Silicates
Natural History Museum of Los Angeles County
http://www.nhm.org/lacmnh/departments/
research/mineralogy/silicates/index.htm
Lizardite?
14
Si Tetrahedral Layers (SiO2)
Triangular Pyramid
Si4+ in Center
O2- at Nodes
#
Si Tetrahedral Layers (SiO2)
Triangular Pyramid
Si4+ in Center
O2- at Nodes
#
Si Tetrahedra, in 3 different fashions
#
15
1:1 Sheet Sillicate
#
1:1 Clay: Kaolinite
7 Angstroms
S. Kite Image
1:1 Clay: Kaolinite
7 Angstroms
S. Kite Image
16
2:1 Clays
2 Si Tetrahedral Layers
1 Al Octahedral Layer
2:1 Clay: Illite (Muscovite)
10 Angstroms
S. Kite Image
10 Angstrom Clay: Illite (Muscovite)
v
v
v
Al3+ Substitutes for Si4+ in
Tetrahedral Sheets
v
v
v
v
v
v
Balanced by Interlayer K+
Tiny K+ Ion Fits Easily, So
It Is Tightly Bond.
v
v
v
S. Kite Image
17
2:1 Clay: Vermicullite
14 Angstroms
S. Kite Image
14 Angstrom Clay: Vermiculite
v
v
v
Al3+ Substitutes for Si4+
in Tetrahedra (Like Illite)
v
v
v
v
v
v
Substitution Occurs in
Presence of Larger
Cations (e.g. Ca2+ or
Mg2+) That Don't Fit as
Snugly Between Sheets
v
S. Kite Image
v
14 Angstrom Clay: Vermiculite
v
v
v
v
v
v
v
v
v
v
v
Wide Spacing Allows
Water to Coexist with
Interlayer Cations
Short Strong Bond Does
Not Allow Water to
Escape Except When
Great Heat Is Applied
(150*C)
S. Kite Image
18
2:1 Clay: Smectite (Montmorillonite)
12 to 18 Angstroms
Expandable Clay
animate me
S. Kite Image
12-18 Angstrom Clay: Smectite
Mg2+ or Fe2+
Substitutes for Al3+
in Octahedra
Substitution Occurs in
Presence of Larger
Cations (e.g. Ca2+ or
Mg2+) Held by Weak
Long Bonds
S. Kite Image
Expandable Clay: Smectite
Weak Long Bonds
Allow Interlayer
Oriented Water
Molecules When
Clay Is Saturated
(18 Angstroms)
S. Kite Image
19
Expandable Clay: Smectite
Weak Long Bonds
Allow Interlayer
Water to Escape
When Clay Dries
(12 Angstroms)
S. Kite Image
Expandable Clay: Smectite
S. Kite Image
Expandable Clay: Smectite
S. Kite Image
20
CLAY MINERAL SEQUENCE:
w/ Weathering, Time & Leaching
Micas (Illite) - Vermiculite - Smectite
Intergrades (Mixed-Layered Clays)
Kaolinite
Gibbsite
CLAY MINERAL SEQUENCE:
Alumina Enrichment, Silica Leaching
Micas (Illite) - Vermiculite - Smectite
Si
Intergrades (Mixed-Layered Clays)
Si
Kaolinite
Si
Gibbsite
Next Topic: Soils
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