1 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
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1
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 SeriesHigh-Temperature
Geochemical Equilibrium
2
Bowen’s Reaction Series(for Silicate Minerals)
Low
HighOlivine
Pyroxene
Amphibole
Biotite Na Plagioclase
Ca Plagioclase
Orthoclase
Muscovite
Quartz
Tem
per a
ture
Most Important Igneous Rocks
Mineral Composition
Text
ure
Felsic Mafic Ultra-Mafic
Inter-mediate
Cellular,GlassyFine
Coarse
Mix
rare
rare
rare
peridotite
basalt
gabbro
rhyolite
granite
andesite
diorite
scoriapumice
rhyoliteporphyry
andesiteporphyry
basaltporphyry
basalt
granite
andesiteporphyry
obsidian
basalt
Mineral Composition
Text
ure
Felsic Mafic Ultra-MaficIntermediate
Cell, Glassy
Fine
Coarse
Mix
rare
rare
rare
peridotitegabbro
rhyolite
granite
andesite
diorite
scoriapumice
rhyoliteporphyry
andesiteporphyry
basaltporphyry
obsidian
Olivine
Pyroxene
Am
phibole
Biotite
Na Plag
Ca Plag
Orthoclase
MuscoviteQ
uartz
Bowen’s Reaction Series & Igneous Rock Classification
3
Bowen’s Reaction Series(for Silicate Minerals)
Low
HighOlivine
Pyroxene
Amphibole
Biotite Na Plagioclase
Ca Plagioclase
Orthoclase
Muscovite
Quartz
Tem
per a
ture
Goldich (1938) Stability Series(for Sand & Silt)
Olivine
Pyroxene
Amphibole
Biotite Na PlagioclaseCa Plagioclase
Orthoclase
Muscovite
Quartz
Stab
leUns
tabl
e
M.L. Jackson's Weathering Index (1968) for Clay-size Particles (Partial List)1. Gypsum, Halite, Anhydrite2. Calcite, Apatite3. Olivine, Pyroxene, Amphibole4. Biotite, Glauconite5. Albite, Anorthite, Obsidian6. Quartz, Cristobalite7. Muscovite, Sericite*8. Vermiculite*9. Smectite*10. Kaolinite*11. Gibbsite*12. Hematite*, Goethite*13. Rutile, Zircon* = Weathering ProductsRock-forming Minerals Underlined
Leave Room for all this!
4
1. Gypsum, Halite, Anhydrite2. Calcite, Apatite3. Olivine, Pyroxene, Amphibole4. Biotite, Glauconite5. Albite, Anorthite, Obsidian6. Quartz, Cristobalite7. Muscovite, Sericite*
Jackson's Weathering Indexfor Clay-Sized Particles
8. Vermiculite*9. Smectite*10. Kaolinite*11. Gibbsite*12. Hematite*, Goethite*13. Rutile, Zircon* = Weathering ProductsRock-forming Minerals Underlined
Jackson's Weathering Indexfor Clay-Sized Particles
Types of Chemical Weathering Reactions (List, Cover)
1. Solution2. Oxidation-reduction3. Carbonation4. Hydration5. Chelation6. Ion Exchange7. Hydrolysis
5
1. Solution
CaCO3 = Ca2+(aq) + CO3
2-(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
Eh = Redox Potential:
Ability of an Environment to Yield or Absorb Electrons
Electron Volts:+ Favors Oxidation- Favors Reduction
6
Stability Fields ofHematite and
Magnetite in Water
Source:
Garrels, Robert M., and Christ, Charles L., 1965, Solution, Minerals, and Equilibria: San Francisco, Freeman, Cooper & Company, 450 p.
Source:
Garrels, Robert M., and Christ, Charles L., 1965, Solution, Minerals, and Equilibria: San Francisco, Freeman, Cooper & Company, 450 p.
Stability Fields ofCu - Fe – S - O - H
System
Think About Complexity of Real World with 92 Elements
AMD =Acid Mine Drainage
Dobbin, WV
Fe(OH)3(s) = “Yellow Boy”
Pyrite
FeS2 = Pyrite
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Acid Mine Drainage EquationsFrom Renton, Stiller & Rymer (1989)
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 SO4
2- + 16 H+
Fe2+ : FerrousFe3+ : Ferric
FeS2 = PyriteFe(OH)3(s) = “Yellow Boy”
Pyrite
http://www.minerals.net/mineral/index.htm
3. CARBONATION
Native Cu
Malachite (CuCO3.Cu(OH)2)
or Azurite
http://www.minerals.net/mineral/index.htm
4. HYDRATION
Anhydrite → Gypsum
CaSO4 + 2 H2O = CaSO4 n2 H2O
8
5. CHELATION
Complex Organic Process by Which Metallic CationsAre Incorporated Into Hydrocarbon Molecule
Chelation
Ca2+Na+
K+ Mg2+
Fertile Cation-Rich Soil
Chelation
Ca2+Na+
K+ Mg2+
H+H+
H+H+
H+H+
9
Chelation
Ca2+Na+
K+ Mg2+
H+H+
H+H+
H+H+
CationExchange
Chelation
Ca2+ H+
H+
Mg2+
H+ Na+
H+H+
K+H+
Cations TakenInto Plant
Chelation
H+
H+
H+
H+H+
H+
Infertile Cation-Depleted Soil
Cationsin thePlant
10
Oh Shoot!
Chelation
H+
H+
H+
H+
H+
H+
Infertile Cation-Depleted Soil
CationsRecycle into Soil
Cations
6. IONIC EXCHANGECations Substitute for Other Cations
in Crystal LatticeControlled by Ionic Radius, Soil
Particle Charges
Basic Environments:
Na < K < Mg < CaEasy Remove <-----> Held Tight
6. IONIC EXCHANGE
Acid Environment: H+, Al3+
Replace Other Cations
11
Base Saturation (%)=
# Exchangeable Base X100%# Exchangeable Bases + H
With Increased Leaching -- BS Decreases
Decrease BS -- Poor Agriculture Soil
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)
12
Clay Minerals:
Clay Has “Two” Meanings:
Textural:Unified (Engineers): < 5.00 µmWentworth (Geologists): < 3.96 µm Soil Science: < 2.00 µm
Mineralogical: Hydrous Aluminous PhyllosilicatesQuartz-Clay Break Occurs ~ 2 µm
Clay Mineral Tour
Start With Simple and Get More Complicated
Start With Most Stable & Highest Alumina Content
Muscovite Mica (Sheet Silicate)
13
Gibbsite Al(OH)3
Not a True Clay (No Silica) Building Block in Clays.
Al(OH)3 or Al Octahedron
Al
OH-
Two 4-sided Pyramids Stuck Together @ BaseAl3+ in Center, OH- at Nodes
Al(OH)3 OctahedraBuilding Blocks in Clays.
14
Si Tetrahedral Layers (SiO2)
Triangular Pyramid
Si4+ in CenterO2- at Nodes
#
Si Tetrahedral Layers (SiO2)
Triangular Pyramid
Si4+ in CenterO2- at Nodes
#
Si Tetrahedra, in 3 different fashions
#
15
1:1 Sheet Sillicate
#
An Insiders Look at the SilicatesNatural History Museum of Los Angeles County
http://www.nhm.org/lacmnh/departments/research/mineralogy/silicates/index.htm
Lizardite?
Slides Marked with # Were Taken In Part From This Web Site:
1:1 Sheet Sillicate
1:1 Clay: Kaolinite
7 Angstroms
16
1:1 Clay: Kaolinite
7 Angstroms
2:1 Clays
2 Si Tetrahedral Layers1 Al Octahedral Layer
2:1 Clay: Illite (Muscovite)
10 Angstroms
17
10 Angstrom Clay: Illite (Muscovite)
Al3+ Substitutes for Si4+ in Tetrahedral Sheets
Balanced by Interlayer K+
Tiny K+ Ion Fits Easily, So It Is Tightly Bond.
v vv
v vv
vv
v vv
v
2:1 Clay: Vermicullite
14 Angstroms
14 Angstrom Clay: Vermiculite
Al3+ Substitutes for Si4+
in Tetrahedra (Like Illite)
Substitution Occurs in Presence of Larger Cations (e.g. Ca2+ or Mg2+) That Don't Fit as Snugly Between Sheets
vv
v vv
vv
v vv
v
18
14 Angstrom Clay: Vermiculite
Wide Spacing AllowsWater to Coexist with Water to Coexist with Interlayer Cations
Short Strong Bond Does Not Allow WaterWater to Escape Except When Great Heat Is Applied (150*C)
vv
v vv
vv
v vv
v
2:1 Clay: Smectite (Montmorillonite)
12 to 18 Angstroms
Expandable Clayanimate me
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
19
Expandable Clay: Smectite
Weak Long Bonds Allow Interlayer Oriented WaterOriented WaterMolecules When Clay Is Saturated(18 Angstroms)
Expandable Clay: Smectite
Weak Long Bonds Allow Interlayer
WaterWater to Escape When Clay Dries(12 Angstroms)
Expandable Clay: Smectite
20
Expandable Clay: Smectite
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
Intergrades (Mixed-Layered Clays)
Kaolinite
Gibbsite
Si
Si
Si
21
Lecture 5: Soils I
Soil:Assemblage of natural bodies on the
Earth’s surface (natural or artificial)capable of supporting plant life outdoors
Pedon:Area on Earth’s surface w/ single type of soil Also: soil mapping unit.
Soil DevelopmentIs a Function of 5 Factors
S = ƒ (Cl,O,R,P,T)1. Climate2. Organisms3. Relief4. Parent material5. Time
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Factors of Soil Development1. Climate
Effects of Temperature & MoistureRedox Reactions
Fe (Iron) Depletions & ConcentrationsDepletions
Gray Reduced Iron (Water-Logged)Concentrations
Red “Mottles” of Oxidized Iron(= Redoximorphic features)
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