1

Geology and Soils Geology and Soils in Relation to in Relation to

Vadose Zone HydrologyVadose Zone Hydrology

2

Typical Geologic Configurations: floodplainsTypical Geologic Configurations: floodplains

Key points:Key points:narrow continuous banding of narrow continuous banding of

alternating high and low permeabilityalternating high and low permeabilitynot necessarily oriented “down stream”not necessarily oriented “down stream”

Key points:Key points:narrow continuous banding of narrow continuous banding of

alternating high and low permeabilityalternating high and low permeabilitynot necessarily oriented “down stream”not necessarily oriented “down stream”

3

Terraced stream channel with likely Terraced stream channel with likely ephemeral perched water. ephemeral perched water. Terraced stream channel with likely Terraced stream channel with likely ephemeral perched water. ephemeral perched water.

Typical Geologic Configurations: floodplainsTypical Geologic Configurations: floodplains

4

Typical Geologic Configurations: KarstTypical Geologic Configurations: Karst

Karst is water eroded limestone. This creates subsurface channels,some large enough to survey by boat. Equivalent structures (macropores)are also critical in vadose environments.

5

Geologic Configurations: beach depositsGeologic Configurations: beach deposits

Beach deposits, although similar to river deposits in Beach deposits, although similar to river deposits in texture, have unique structuretexture, have unique structure

Generally (not always!) fining upwardGenerally (not always!) fining upwardLaterally extensiveLaterally extensive

Lower variation in energy (more uniform)Lower variation in energy (more uniform)

Beach deposits, although similar to river deposits in Beach deposits, although similar to river deposits in texture, have unique structuretexture, have unique structure

Generally (not always!) fining upwardGenerally (not always!) fining upwardLaterally extensiveLaterally extensive

Lower variation in energy (more uniform)Lower variation in energy (more uniform)

6

Mt St. Helens Ash

Reworked by mammals?

Diagonal micro-bedding

Typical Hanford Formation

7

Typical Geologic Configurations: LavaTypical Geologic Configurations: LavaLava flows may have alternating porous, fractured, Lava flows may have alternating porous, fractured, and low permeability regions with sedimentary and low permeability regions with sedimentary deposits between flowsdeposits between flows

8

Typical Geologic ConfigurationsTypical Geologic Configurations Fractures, Dikes, Fill

9

Geologic Configurations: various “aquifers”Geologic Configurations: various “aquifers”

What’s an aquifer? Water that will flow into a well…What’s an aquifer? Water that will flow into a well…What’s an aquifer? Water that will flow into a well…What’s an aquifer? Water that will flow into a well…

10

Water Tables (continued)Water Tables (continued)

Many aquifer systems have perched Many aquifer systems have perched water tables that can be productivewater tables that can be productiveMany aquifer systems have perched Many aquifer systems have perched water tables that can be productivewater tables that can be productive

11

A Primer on Properties and A Primer on Properties and Description of Natural MediaDescription of Natural Media

Particle Size DistributionParticle Size Distribution

Soil ClassificationSoil Classification

Clay mineralogyClay mineralogy

Particle Size DistributionParticle Size Distribution

Soil ClassificationSoil Classification

Clay mineralogyClay mineralogy

12

Hey, like, why do we care?Hey, like, why do we care?

Transport through natural porous Transport through natural porous media cannot be understood from media cannot be understood from mathematical notation and mathematical notation and boundary conditions alone.boundary conditions alone.

The structure, setting, history and The structure, setting, history and chemistry of the mineral system in chemistry of the mineral system in the vadose zone all play central the vadose zone all play central roles in transport. roles in transport.

Transport through natural porous Transport through natural porous media cannot be understood from media cannot be understood from mathematical notation and mathematical notation and boundary conditions alone.boundary conditions alone.

The structure, setting, history and The structure, setting, history and chemistry of the mineral system in chemistry of the mineral system in the vadose zone all play central the vadose zone all play central roles in transport. roles in transport.

13

The ultra-basicsThe ultra-basics

Particle size distribution is plotted Particle size distribution is plotted as the mass which is made up of as the mass which is made up of particles smaller than a given size.particles smaller than a given size.

Very useful in estimating the soil’s Very useful in estimating the soil’s hydraulic properties such as the hydraulic properties such as the water retention characteristics and water retention characteristics and the hydraulic conductivity. the hydraulic conductivity.

Particle size distribution is plotted Particle size distribution is plotted as the mass which is made up of as the mass which is made up of particles smaller than a given size.particles smaller than a given size.

Very useful in estimating the soil’s Very useful in estimating the soil’s hydraulic properties such as the hydraulic properties such as the water retention characteristics and water retention characteristics and the hydraulic conductivity. the hydraulic conductivity.

14

StandardStandard

sievesieve

sizessizes

StandardStandard

sievesieve

sizessizes

15

Typical Particle Size PlotTypical Particle Size Plot

Particle Size, d (mm)

% M

ass

< d

0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10

16

Summary statistics for particle Summary statistics for particle size distributionsize distribution

dd5050, d, d1010, d, d80 etc.80 etc.

Uniformity coefficient, UUniformity coefficient, U

U = U = d d6060 /d /d1010 [1.1][1.1]

U between 2 and 10 for “well sorted” and U between 2 and 10 for “well sorted” and “poorly sorted” materials“poorly sorted” materials

dd5050, d, d1010, d, d80 etc.80 etc.

Uniformity coefficient, UUniformity coefficient, U

U = U = d d6060 /d /d1010 [1.1][1.1]

U between 2 and 10 for “well sorted” and U between 2 and 10 for “well sorted” and “poorly sorted” materials“poorly sorted” materials

17

Dependence of bulk density on Dependence of bulk density on particle size distributionparticle size distribution

Uniform particle size distribution givesUniform particle size distribution giveslow packing densitylow packing density

increasing the range of particle sizes increasing the range of particle sizes gives rise to greater bulk density.gives rise to greater bulk density.

Uniform particle size distribution givesUniform particle size distribution giveslow packing densitylow packing density

increasing the range of particle sizes increasing the range of particle sizes gives rise to greater bulk density.gives rise to greater bulk density.

18

% S

mal

ler

0

100

Size

% S

mal

ler

0

100

Size

% S

mal

ler

0

100

Size

"Well Sorted" "Poorly Sorted"

% S

mal

ler

0

100

Size

% S

mal

ler

0

100

Size

% S

mal

ler

0

100

Size

(a)

(b)

"Poorly Graded" "Well Graded"

19

What are is the basis of size What are is the basis of size classes?classes?

ClayClay: : won’t settle (<2: doesn’t feel gritty between your teeth).

SiltSilt: : settles freely, but cannot be discriminated by eye (isn’t slippery between your fingers; doesn’t make strong ribbons; goes through a number 300 sieve; 2<silt<0.05mm).

SandSand: : you can see (>0.05 mm), but is smaller than pebbles (<2mm).

ClayClay: : won’t settle (<2: doesn’t feel gritty between your teeth).

SiltSilt: : settles freely, but cannot be discriminated by eye (isn’t slippery between your fingers; doesn’t make strong ribbons; goes through a number 300 sieve; 2<silt<0.05mm).

SandSand: : you can see (>0.05 mm), but is smaller than pebbles (<2mm).

20

Systems of soil textural classificationSystems of soil textural classification

(The USDA is standard in the US)(The USDA is standard in the US)(The USDA is standard in the US)(The USDA is standard in the US)

21

Sand, Silt, Clay – Textural TriangleSand, Silt, Clay – Textural Triangle

Standard textural triangle for mixed grain-size materials

Standard textural triangle for mixed grain-size materials

Clay axis

Silt a

xis

Sand axis

22

Soil ClassificationSoil Classification

Based on present features and formative processes

Soil is geologic material which has been altered by weathering an biological activity. Typically extends 1-2 meters deep; below soil is “parent material”

Soil development makes sequence of bands, or horizons.

Based on present features and formative processes

Soil is geologic material which has been altered by weathering an biological activity. Typically extends 1-2 meters deep; below soil is “parent material”

Soil development makes sequence of bands, or horizons.

23

Eluvial processesEluvial processes

Clay is carried with water in eluviation and deposited in illuviation in sheets (lamellae) making an argillic horizon.

Soluble minerals may be carried upward through a soil profile driven by evaporation giving rise to concentrated bands of minerals at particular elevations.

Clay is carried with water in eluviation and deposited in illuviation in sheets (lamellae) making an argillic horizon.

Soluble minerals may be carried upward through a soil profile driven by evaporation giving rise to concentrated bands of minerals at particular elevations.

24

Vertical Variations in SoilsVertical Variations in Soils

Banding also arises from the depositional processes (parent material).

The scale of variation shorter in the vertical than horizontal.

Layers may be very distinct, or almost indistinguishable.

Banding also arises from the depositional processes (parent material).

The scale of variation shorter in the vertical than horizontal.

Layers may be very distinct, or almost indistinguishable.

25

System of designationsSystem of designations

Three symbol designation e.g. “Ap1”

“A” here is what is referred to as the designation of master horizon

There are six master horizon designations; O, A, E, B, C, and R.

Three symbol designation e.g. “Ap1”

“A” here is what is referred to as the designation of master horizon

There are six master horizon designations; O, A, E, B, C, and R.

26

Master Horizon DesignationsMaster Horizon DesignationsO: dominated by organic matter.

A: first mineral horizon in a soil with either enriched humic material or having properties altered by agricultural activities (e.g., plowing, grazing).

E: loss of a combination of clay, iron and aluminum; only resistant materials. Lighter in color than the A horizon above it (due to a paucity of coatings of organic matter and iron oxides).

O: dominated by organic matter.

A: first mineral horizon in a soil with either enriched humic material or having properties altered by agricultural activities (e.g., plowing, grazing).

E: loss of a combination of clay, iron and aluminum; only resistant materials. Lighter in color than the A horizon above it (due to a paucity of coatings of organic matter and iron oxides).

27

Master Horizon Designations (cont.)Master Horizon Designations (cont.)

B: below A or E, enriched in colorants (iron and clays), or having significant block structure.

C: soil material which is not bedrock, but shows little evidence of alteration from the parent material.

R: too tough to penetrate with hand operated equipment.

For complete definitions, see the SCS Soil Taxonomy (Soil Conservation Service, 1994).

B: below A or E, enriched in colorants (iron and clays), or having significant block structure.

C: soil material which is not bedrock, but shows little evidence of alteration from the parent material.

R: too tough to penetrate with hand operated equipment.

For complete definitions, see the SCS Soil Taxonomy (Soil Conservation Service, 1994).

28

Master Horizon Designations (cont.)Master Horizon Designations (cont.)

Major designations may be combined as either AB or A/B if the horizon has some properties of the second designation

Major designations may be combined as either AB or A/B if the horizon has some properties of the second designation

29

Subordinate classificationsSubordinate classifications

Lower case letter indicates master Lower case letter indicates master horizon features. horizon features. There are 22. e.g.There are 22. e.g.k = accumulation of carbonatesk = accumulation of carbonatesp = plowingp = plowingn = accumulation of sodiumn = accumulation of sodium

May be used in multipleMay be used in multiple

Lower case letter indicates master Lower case letter indicates master horizon features. horizon features. There are 22. e.g.There are 22. e.g.k = accumulation of carbonatesk = accumulation of carbonatesp = plowingp = plowingn = accumulation of sodiumn = accumulation of sodium

May be used in multipleMay be used in multiple

30

Final notes on designationsFinal notes on designations

Arabic numerals allow description of Arabic numerals allow description of sequences with the same master, but sequences with the same master, but with differing subordinate (e.g., Bk1 with differing subordinate (e.g., Bk1 followed by Bn2). followed by Bn2).

Whenever a horizon is designated, its Whenever a horizon is designated, its vertical extent must also be reported.vertical extent must also be reported.

Arabic numerals allow description of Arabic numerals allow description of sequences with the same master, but sequences with the same master, but with differing subordinate (e.g., Bk1 with differing subordinate (e.g., Bk1 followed by Bn2). followed by Bn2).

Whenever a horizon is designated, its Whenever a horizon is designated, its vertical extent must also be reported.vertical extent must also be reported.

31

Color and Structure tell genetic Color and Structure tell genetic and biogeochemical history and biogeochemical history Dark colors are indicative of high organic

contentGrayish coloration indicates reducing (oxygen

stripping) conditionsReddish color indicates oxidizing (oxygen

supplying) conditions. Relates closely to hydraulic conditions of site

Often of greater use than a slew of lab analysis of soil cores.

Dark colors are indicative of high organic content

Grayish coloration indicates reducing (oxygen stripping) conditions

Reddish color indicates oxidizing (oxygen supplying) conditions.

Relates closely to hydraulic conditions of site

Often of greater use than a slew of lab analysis of soil cores.

32

Quantification of ColorQuantification of Color

Munsell Color chart by hue, value and Munsell Color chart by hue, value and chroma; summarized in an alpha-numerical chroma; summarized in an alpha-numerical coding shorthand. coding shorthand.

Pattern of coloration is informative. Pattern of coloration is informative. Mottling, where color varies between grayish Mottling, where color varies between grayish to reddish over a few cm, most important. to reddish over a few cm, most important.

Intermittent saturation; oxidizing then Intermittent saturation; oxidizing then reducingreducing

Precise terminology for mottle description Precise terminology for mottle description (e.g., Vepraskas, M.J. 1992).(e.g., Vepraskas, M.J. 1992).

Munsell Color chart by hue, value and Munsell Color chart by hue, value and chroma; summarized in an alpha-numerical chroma; summarized in an alpha-numerical coding shorthand. coding shorthand.

Pattern of coloration is informative. Pattern of coloration is informative. Mottling, where color varies between grayish Mottling, where color varies between grayish to reddish over a few cm, most important. to reddish over a few cm, most important.

Intermittent saturation; oxidizing then Intermittent saturation; oxidizing then reducingreducing

Precise terminology for mottle description Precise terminology for mottle description (e.g., Vepraskas, M.J. 1992).(e.g., Vepraskas, M.J. 1992).

33

StructureStructure

Must identify the smallest repeated Must identify the smallest repeated element which makes up the “soil ped” element which makes up the “soil ped” Include details of the size, strength, Include details of the size, strength, shape, and distinctness of the shape, and distinctness of the constituent peds.constituent peds.

Must identify the smallest repeated Must identify the smallest repeated element which makes up the “soil ped” element which makes up the “soil ped” Include details of the size, strength, Include details of the size, strength, shape, and distinctness of the shape, and distinctness of the constituent peds.constituent peds.

34

Climate Climate Six major climatic categories employed in soil Six major climatic categories employed in soil classification; useful in groundwater recharge and classification; useful in groundwater recharge and vadose zone transport.vadose zone transport. Aquic: precipitation always exceeds evapotransiration (ET), Aquic: precipitation always exceeds evapotransiration (ET),

yielding continuous net percolation.yielding continuous net percolation.Xeric: recharge occurs during the wet cool season, while Xeric: recharge occurs during the wet cool season, while

the soil profile is depleted of water in the hot season. the soil profile is depleted of water in the hot season.

Identifying the seasonality of the local water balance is Identifying the seasonality of the local water balance is fundamental to understanding the vadose zone fundamental to understanding the vadose zone

hydrology.hydrology.

Six major climatic categories employed in soil Six major climatic categories employed in soil classification; useful in groundwater recharge and classification; useful in groundwater recharge and vadose zone transport.vadose zone transport. Aquic: precipitation always exceeds evapotransiration (ET), Aquic: precipitation always exceeds evapotransiration (ET),

yielding continuous net percolation.yielding continuous net percolation.Xeric: recharge occurs during the wet cool season, while Xeric: recharge occurs during the wet cool season, while

the soil profile is depleted of water in the hot season. the soil profile is depleted of water in the hot season.

Identifying the seasonality of the local water balance is Identifying the seasonality of the local water balance is fundamental to understanding the vadose zone fundamental to understanding the vadose zone

hydrology.hydrology.

35

Six categories of climatesSix categories of climatesSix categories of climatesSix categories of climates

36

High Points of Clay MineralogyHigh Points of Clay Mineralogy

GeneralGeneral

Clay constituents dominate hydraulic Clay constituents dominate hydraulic chemical behavior chemical behavior

Two basic building blocks of claysTwo basic building blocks of clayssilica centered tetrahedra silica centered tetrahedra variously centered octahedra variously centered octahedra

GeneralGeneral

Clay constituents dominate hydraulic Clay constituents dominate hydraulic chemical behavior chemical behavior

Two basic building blocks of claysTwo basic building blocks of clayssilica centered tetrahedra silica centered tetrahedra variously centered octahedra variously centered octahedra

37

Basic FormationsBasic Formations

chain structures chain structures (e.g., asbestos)(e.g., asbestos)

amorphous structures amorphous structures (glasses)(glasses)

sheet structure sheet structure (phyllosilicates; clay!) (phyllosilicates; clay!)

chain structures chain structures (e.g., asbestos)(e.g., asbestos)

amorphous structures amorphous structures (glasses)(glasses)

sheet structure sheet structure (phyllosilicates; clay!) (phyllosilicates; clay!)

http://usgsprobe.cr.usgs.gov/gpm/dickite.gif

http://whyfiles.org/coolimages/images/csi/asbestos.jpg

38

Unit-cells octa- and tetrahedral unitsUnit-cells octa- and tetrahedral units

http://www.pssc.ttu.edu/pss2330/images/uday15_1_3.gifhttp://www.pssc.ttu.edu/pss2330/images/uday15_1.gif

www.georgehart.com/virtual-polyhedra/ dice.html

39

Isomorphic SubstitutionIsomorphic SubstitutionSilica tetrahedron: four oxygen surrounding one silica atomSpace filled by the silica can accommodate atoms up to

0.414 times O2 radius (5.8 x 10-9 m): includes silica and aluminum.

Balanced charge if the central atom has charge +4, negative charge if the central atom has a less positive charge (oxygen is shared by two tetrahedra in crystal so contributes -1 to each cell).

Same for the octahedra: 0.732 times O2 radius (1.02 x 10-8 m): iron, magnesium, aluminum, manganese, titanium, sodium or calcium, (sodium and calcium generate cubic lattice rather than octahedra)

Silica tetrahedron: four oxygen surrounding one silica atomSpace filled by the silica can accommodate atoms up to

0.414 times O2 radius (5.8 x 10-9 m): includes silica and aluminum.

Balanced charge if the central atom has charge +4, negative charge if the central atom has a less positive charge (oxygen is shared by two tetrahedra in crystal so contributes -1 to each cell).

Same for the octahedra: 0.732 times O2 radius (1.02 x 10-8 m): iron, magnesium, aluminum, manganese, titanium, sodium or calcium, (sodium and calcium generate cubic lattice rather than octahedra)

40

Ionic radii dictate isomorphic substitutionIonic radii dictate isomorphic substitutionIon Ionic

radius. nm

Rx: Ro

O2- 0.140 -- F- 0.133 -- Cl- 0.181 -- Si4+ 0.039 0.278 Al3+ 0.051 0.364 Fe3+ 0.064 0.457 Mg2+ 0.066 0.471 Ti4+ 0.068 0.486 Fe2+ 0.074 0.529 Mn2+ 0.080 0.571 Na+ 0.097 0.693 Ca2+ 0.099 0.707 K+ 0.133 0.950

Ba2+ 0.134 0.957 Rb+ 0.147 1.050

Fit into Tetrahedron (radius <0.41 times that of oxygen Fit into Octahedron (radius <0.732 times that of oxygen)

41

Surface Functional GroupsSurface Functional GroupsClay minerals surfaces made up of hexagonal rings of

tetrahedra or octahedra.

The group of atoms in these rings act as a delocalized source of negative charge; surface functional group (a.k.a. SFG).

Cations attracted to center of SFG’s above surface of the sheet.

Some (e.g., K+ and NH4+) dehydrated and attached to the SFG: inner

sphere complex with the SFG Cations bound to the SFG by water: outer sphere complex

Inner and outer sphere ion/clay complexes are the Stern layer.

Clay minerals surfaces made up of hexagonal rings of tetrahedra or octahedra.

The group of atoms in these rings act as a delocalized source of negative charge; surface functional group (a.k.a. SFG).

Cations attracted to center of SFG’s above surface of the sheet.

Some (e.g., K+ and NH4+) dehydrated and attached to the SFG: inner

sphere complex with the SFG Cations bound to the SFG by water: outer sphere complex

Inner and outer sphere ion/clay complexes are the Stern layer.

42

Details of Stearn LayerDetails of Stearn LayerAnions will be repelled from clay

surfaces.

Zig-zag negative and positively charged elements in clay generates dipole moment attracting charged particles.

Diffuse attraction results in increased ionic concentration: Gouy layer (Gouy, 1910).

Dipole-dipole attraction also holds water to the clay surfaces, in addition to osmotic force from cation concentration near the clay surfaces.

Anions will be repelled from clay surfaces.

Zig-zag negative and positively charged elements in clay generates dipole moment attracting charged particles.

Diffuse attraction results in increased ionic concentration: Gouy layer (Gouy, 1910).

Dipole-dipole attraction also holds water to the clay surfaces, in addition to osmotic force from cation concentration near the clay surfaces.

http://www.ornl.gov/ORNLReview/v34_2_01/p24a.jpg

43

Hydration of CationsHydration of Cationshttp://www-sst.unil.ch/perso_pages/Bernhard_homepage/On%20line%20publications/Image31.gif

44

Cation ExchangeCation ExchangeThe degree to which soil cations may be swapped for other cations is quantified as the cation exchange capacity (CEC) which is measured as

CEC = cmol of positive charge/kgcmol(+) is equal to 10 Milliequivilents (meq)

1 CEC =1 meq per 100 grams of soil.

Typical values of CEC are less than 10 for Kaolinite, between 15 and 40 for illite, and between 80 and 150 for montmorilonite.

The degree to which soil cations may be swapped for other cations is quantified as the cation exchange capacity (CEC) which is measured as

CEC = cmol of positive charge/kgcmol(+) is equal to 10 Milliequivilents (meq)

1 CEC =1 meq per 100 grams of soil.

Typical values of CEC are less than 10 for Kaolinite, between 15 and 40 for illite, and between 80 and 150 for montmorilonite.

45

Swelling of ClaysSwelling of Clays

(a) Low moisture: clays bound (b) High moisture: clays dissociated

= H O2

clay plate

clay plate clay plate

clay plate

46

Distinguishing features between claysDistinguishing features between clays

Order of layering of tetra and octa Order of layering of tetra and octa sheetssheets

Isomorphic substitutionsIsomorphic substitutions

Cations which are bound to the Cations which are bound to the surface functional groups surface functional groups

Order of layering of tetra and octa Order of layering of tetra and octa sheetssheets

Isomorphic substitutionsIsomorphic substitutions

Cations which are bound to the Cations which are bound to the surface functional groups surface functional groups

47

Examples: KaoliniteExamples: Kaolinite

1:1 alternating octa:tetra1:1 alternating octa:tetra sheets sheets

Little isomorphic substitution. Little isomorphic substitution.

Thus...Thus...Very stable thicker stacksVery stable thicker stacksRelatively low surface area: 7-30 mRelatively low surface area: 7-30 m22/gr/grDo not swell muchDo not swell much

1:1 alternating octa:tetra1:1 alternating octa:tetra sheets sheets

Little isomorphic substitution. Little isomorphic substitution.

Thus...Thus...Very stable thicker stacksVery stable thicker stacksRelatively low surface area: 7-30 mRelatively low surface area: 7-30 m22/gr/grDo not swell muchDo not swell much

http://www.arenisca.com/kaol-2.gif

48

Examples: Examples: Montmorilonite Montmorilonite

(smectite family)(smectite family)

The most common smectite is Montmorillinite, with general formula :

(½Ca,Na)(Al,Mg,Fe)4(Si,Al)8O20(OH)4.nH2O

2:1 octa sandwiched in 2:1 octa sandwiched in 2 tetra sheets. 2 tetra sheets.

Lots of isomorphic Lots of isomorphic substitution:substitution:MgMg+2+2, Fe, Fe+2+2, & Fe, & Fe+3+3 for Al for Al+3 +3 in octa. Since the octa is in octa. Since the octa is between tetra’s, cations in outer sphere complexes with between tetra’s, cations in outer sphere complexes with hydrated SFG’s. hydrated SFG’s.

Thus:Thus:High surface area (600-800 mHigh surface area (600-800 m22/gr)/gr)Lots of swellingLots of swellingBig CEC. Big CEC.

The most common smectite is Montmorillinite, with general formula :

(½Ca,Na)(Al,Mg,Fe)4(Si,Al)8O20(OH)4.nH2O

2:1 octa sandwiched in 2:1 octa sandwiched in 2 tetra sheets. 2 tetra sheets.

Lots of isomorphic Lots of isomorphic substitution:substitution:MgMg+2+2, Fe, Fe+2+2, & Fe, & Fe+3+3 for Al for Al+3 +3 in octa. Since the octa is in octa. Since the octa is between tetra’s, cations in outer sphere complexes with between tetra’s, cations in outer sphere complexes with hydrated SFG’s. hydrated SFG’s.

Thus:Thus:High surface area (600-800 mHigh surface area (600-800 m22/gr)/gr)Lots of swellingLots of swellingBig CEC. Big CEC.

http://www.dc.peachnet.edu/~janderso/acres/Sum99/talksan/img018.gif

49

Examples: IlliteExamples: Illite

2:1 octa sandwiched in 2:1 octa sandwiched in 2 tetra sheets. 2 tetra sheets.

Lots of isomorphic substitution:Lots of isomorphic substitution:AlAl+3+3 for the Si for the Si+4 +4 in the tetra. in the tetra. Generates charged SFG’s binding Generates charged SFG’s binding potassium ionically between the potassium ionically between the successive 2:1 units. successive 2:1 units.

Thus:Thus:Moderate surface area 65-120 mModerate surface area 65-120 m22/g)/g)Little swelling Little swelling moderate CEC. moderate CEC.

2:1 octa sandwiched in 2:1 octa sandwiched in 2 tetra sheets. 2 tetra sheets.

Lots of isomorphic substitution:Lots of isomorphic substitution:AlAl+3+3 for the Si for the Si+4 +4 in the tetra. in the tetra. Generates charged SFG’s binding Generates charged SFG’s binding potassium ionically between the potassium ionically between the successive 2:1 units. successive 2:1 units.

Thus:Thus:Moderate surface area 65-120 mModerate surface area 65-120 m22/g)/g)Little swelling Little swelling moderate CEC. moderate CEC.

http://www.curtin.edu.au/curtin/centre/cems/report_2000/images/41_7.jpg

http://www.glossary.oilfield.slb.com/Files/thumb_OGL98084.jpg

50

Summary of ClaysSummary of ClaysClays are 10’s atomic radii thick and thousands of atomic radii in horizontal extent: high surface to weight area plate structure. Hold both water and cationsHighly reactive. Swell wetted state due to hydration. Dissociate if cations which glue layers together are

depletedPaths tortuous: high resistance to flow of water

“impermeable”Careful in the vadose zone: shrinkage voids

Clays are 10’s atomic radii thick and thousands of atomic radii in horizontal extent: high surface to weight area plate structure. Hold both water and cationsHighly reactive. Swell wetted state due to hydration. Dissociate if cations which glue layers together are

depletedPaths tortuous: high resistance to flow of water

“impermeable”Careful in the vadose zone: shrinkage voids