lecture 4: chemical weathering, “clay” minerals, &...

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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

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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

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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!

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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

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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

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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

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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+

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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

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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

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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)

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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)

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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.

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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

#

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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

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1:1 Clay: Kaolinite

7 Angstroms

2:1 Clays

2 Si Tetrahedral Layers1 Al Octahedral Layer

2:1 Clay: Illite (Muscovite)

10 Angstroms

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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

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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

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Expandable Clay: Smectite

Weak Long Bonds Allow Interlayer Oriented WaterOriented WaterMolecules When Clay Is Saturated(18 Angstroms)


Weak Long Bonds Allow Interlayer

WaterWater to Escape When Clay Dries(12 Angstroms)


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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

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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)

lecture 4: chemical weathering, “clay” minerals, &...

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