building soil minerals. expected ion corrdination

Building Soil Minerals

EXPECTED ION CORRDINATION

OH

Al

OH

OH

OH

OH

OH

-1/2

-1/2 -1/2

-1/2-1/2

-1/2

BOND VALENCE

BOND VALENCE

O

SiO

OO

11

11

xy

z

Clay Minerals

SiO4 Al(OH)6 Mg(OH)6

O

SiO

OO

OH

Al

OH

OH

OH

OHOH

OH

Mg

OH

OH

OH

OHOH

BUILDING BLOCKS

xy

zSi6O18

x y

z

x

y

z

Tetrahedral Sheet

Side View(100) plane

Top View(001) plane

xy

z

Structural Views: Anion Sheets

Creating Octahedral Sheets- Filling of Anion Sheets

Dioctahedral (trivalent ions) and Trioctahedral (divalent ions)

y

x

z

(di)OCTAHEDRAL SITE FILLING Anion Sheet with Trivalent (Al3+) Cations

z

x y

(di)OCTAHEDRAL SITE FILLING Dioctahedral Sheet Without Basal Hydroxyls

Octahedral Sheets

Trioctahedral(divalent cation)

Dioctahedral(trivalent cation)

Viewdown[001] axis

x

y

Charge Development

• Isomorphic substitution• Terminal (unsatisfied) bonds

Charge Development

• Isomorphic Substitution

Tetrahedral Sites:

Al3+ for Si4+ (-) charge

Octahedral Sites:

Mg2++ for Al3+ (-) charge

Al3+ for Mg2+ (+) charge

Al

OH

OH

Al

OH

OH

OH

Al

OH

OH

Al

OH

OH

OH2

2

+ 2 H+

+1/2

+1/2-1/2

-1/2

surface surface

Charge Development• Terminal (unsatisfied) bonds

- bond valence considerations

Minerals within Soils

Rock

Entisol

Inceptisol

Alfisol

Ultisol

Oxisol

Mollisol Vertisol (clay mineralogy)

Ideal Weathering Series

RockEntisol

Inceptisol

Alfisol

Ultisol

Mollisol

Oxisol

Phyllosilicates: Clay Minerals

Entisol

Inceptisol

Alfisol

Ultisol

Mollisol

- Phyllosilicates dominate the clay size particles of most soils

Layer Type Charge† Trioctahedral Dioctahedral

1 octahedra 0 brucite, Mg(OH)2 gibbsite, Al(OH)3

1 tet. : 1 oct. 0 serpentine, Mg3Si2O5(OH)4 kaolinite, Al2Si2O5(OH)4

2 tet. : 1 oct. 0 talc, Mg3Si4O10(OH)2 pyrophyllite, Al2Si4O10(OH)

2 tet: 1 oct. 1 phlogopite muscovite

KMg3(AlSi3O10)(OH)2 KAl2(AlSi3O10)(OH)2

1 biotite

KFe3(AlSi3O10)(OH)2

0.6-0.8 illite (hydrous mica)

K(Na,Ca) Al1.3Fe0.4Mn0.2Si3.4Al0.6O10(OH)2

0.6-0.9 vermiculite

0.25-0.6 smectite

† The layer charge per formula unit

General Classes (layer build-up) of Phyllosilicate Minerals

Octahedral Minerals

x y

z

x y

z

Oct.

Brucite, Mg(OH)2

Gibbsite, Al(OH)3

xy

z

H-bonds

H-bonds

1:1 Phyllosilicates

tet

oct

Sheets

} 1:1 layer

Kaolinite and Serpentine

Kaolinite: Al2Si2O5(OH)4

- dioctahedral, 1:1 mineral

x y

z

Sharing of Apical Oxygens in Tetrahdral Sheet withHydroxyls of Two Octahedral Sheets

tet

oct

tet

Talc (2:1 trioctahedral mineral)

Phlogopite: KMg3(AlSi3O10)(OH)2

Biotite: KFe3(AlSi3O10)(OH)2

Muscovite: KAl2(AlSi3O10)(OH)2

Micas tetoct

tet

tetoct

tet

K+ K+ K+

Unit layer of charge

yx

z

y

x

z

KK++

x

y

z

Si6O18

Ditrigonal (hexagonal) Cavity

Illite (hydrous mica)

Vermiculite

Smectite

Expandable 2:1 Layer Phyllosilicates

tetoct

tet

tetoct

tet

K+H2O Ca2+ H2O H2O

Illite: KAl1.3Fe0.4Mg0.2Si3.4Al0.6O10(OH)2

Vermiculite

dioctahedral: Nax(Al,Fe)2(Si4-xAlx)O10(OH)2 nH2O

trioctahedral: Nax(Mg,Fe)3(Si4-xAlx)O10(OH)2 nH2O

Expandable 2:1 Layer Phyllosilicates

tetoct

tet

tetoct

tet

K+H2O Ca2+ H2O H2O

Expandable 2:1 Layer Phyllosilicates

Smectite

Dioctahedral Forms:

Montmorillonite Nax(Al 2-xMgx)Si4O10(OH)2

Beidellite: Nax(Al 2)(AlxSi4-x)O10(OH)2

Trioctahedral Forms:

Saponite: Nax-y(Mg3-yAly)3(Si4-xAlx)O10(OH)2

Hectorite: Nax(Mg3-xLix)3Si4O10(OH)2

Interlayer ExpansionTwo Dominant Factors:

1. Structural Charge

2. Interlayer Ion

[Mg2Al1(OH )6]Mg3(Si3Al)O10(OH)2

2:1:1 Layer Phyllosilicates

oct (b)

2:1:1 Layer Phyllosilicates

Hydroxy Interlayer Vermiculite (HIV)

Hydroxy Interlayer Smectite (HIS)

- pedogenic chlorites versus true chlorites

tetoct

tet

tetoct

tet

[Mg2Al1(OH )6]Mg3(Si3Al)O10(OH)2

Iron Oxides

Aluminum Oxides

Manganese Oxides

Accessory Minerals

Andisol

- volcanic ash

Hydrous Silicates and Aluminosilicates

Accessory Minerals

Hydrous Silicates and Aluminosilicates

Accessory Minerals100 nm100 nm

Identifying Soil Minerals

X-ray Diffraction

Useful (Common) Methods/Approaches

Optical Microscopy

Infrared Spectroscopy

Thermal Analysis

X-ray Diffraction (XRD)

Physical Properties

X-ray Diffraction

Attributes

Limitations

xy

z

X-ray Diffraction: Foundation

Consider wave properties

X-ray Diffraction: Foundation

Constructive versus Destructive Interference

xy

z

X-ray Diffraction: Foundation

Bragg’s Law: n = 2d sin

d

wavelength

to 2.5 Å)

Layer Type Charge† Trioctahedral Dioctahedral

1 octahedra 0 brucite, Mg(OH)2 gibbsite, Al(OH)3

1 tet. : 1 oct. 0 serpentine, Mg3Si2O5(OH)4 kaolinite, Al2Si2O5(OH)4

2 tet. : 1 oct. 0 talc, Mg3Si4O10(OH)2 pyrophyllite, Al2Si4O10(OH)

2 tet: 1 oct. 1 phlogopite muscovite

KMg3(AlSi3O10)(OH)2 KAl2(AlSi3O10)(OH)2

1 biotite

KFe3(AlSi3O10)(OH)2

0.6-0.8 illite (hydrous mica)

K(Na,Ca) Al1.3Fe0.4Mn0.2Si3.4Al0.6O10(OH)2

0.6-0.9 vermiculite

0.25-0.6 smectite

† The layer charge per formula unit

General Classes (layer build-up) of Phyllosilicate Minerals

Trioctahedral Phyllosilicate Minerals

Sheets

x y

z

x y

z

Octahedral Layer Only: Brucite, Mg(OH)2

Oct.

z

x y

z

x y

1:1 Mineral: Serpentine, Mg3Si2O5(OH)4

Tet.

Oct.

x y

z

x y

z

Oct.

Tet.

2:1 Mineral: Talc, Mg3Si4O10(OH)2

Layer Build-up:

z

y

Mineral Mg2+ K+ Glycerol 550 C

Kaolinite 7 7 7 -

Mica 10 10 10 10

Vermiculite 14 10 14 10

Smectite 14-16 12-14 18 10

HIV 14 14 14 10-11

HIS 14-16 14 18 10-11

XRD: Chemical Treatmentd-spacing, Angstroms

Octahedral Minerals

x y

z

x y

z

Oct.

Brucite, Mg(OH)2

Gibbsite, Al(OH)3

Serpentine: Mg3Si2O5(OH)4

- trioctahedral

Kaolinite: Al2Si2O5(OH)4

- dioctahedral

xy

z

Phlogopite: KMg3(AlSi3O10)(OH)2

Biotite: KFe3(AlSi3O10)(OH)2

Muscovite: KAl2(AlSi3O10)(OH)2

Micas tetoct

tet

tetoct

tet

K+ K+ K+

Illite

Vermiculite

Smectite

Expandable 2:1 Layer Phyllosilicates

tetoct

tet

tetoct

tet

K+H2O Ca2+ H2O H2O

oct (b)

2:1:1 Layer Phyllosilicates

Hydroxy Interlayer Vermiculite (HIV)

Hydroxy Interlayer Smectite (HIS)

- pedogenic chlorites versus true chlorites

tetoct

tet

tetoct

tet

[Mg2Al1(OH )6]Mg3(Si3Al)O10(OH)2