Building Soil Minerals

EXPECTED ION CORRDINATION

BOND VALENCE

Clay Minerals

BUILDING BLOCKS

Si 6 O 18

Tetrahedral Sheet Side View (100) plane Top View (001) plane

Structural Views: Anion Sheets

Creating Octahedral Sheets - Filling of Anion Sheets Dioctahedral (trivalent ions) and Trioctahedral (divalent ions)

(di)OCTAHEDRAL SITE FILLING Anion Sheet with Trivalent (Al 3+ ) Cations

(di)OCTAHEDRAL SITE FILLING Dioctahedral Sheet Without Basal Hydroxyls

Octahedral Sheets Trioctahedral (divalent cation) Dioctahedral (trivalent cation) View down [001] axis x y

Charge Development Isomorphic substitution Terminal (unsatisfied) bonds

Charge Development Isomorphic Substitution Tetrahedral Sites: Al 3+ for Si 4+  (-) charge Octahedral Sites: Mg 2+ + for Al 3+  (-) charge Al 3+ for Mg 2+  (+) charge

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

Rock Entisol Inceptisol Alfisol Ultisol Mollisol Oxisol

Phyllosilicates: Clay Minerals Entisol Inceptisol Alfisol Ultisol Mollisol - Phyllosilicates dominate the clay size particles of most soils

General Classes (layer build-up) of Phyllosilicate Minerals

Octahedral Minerals Oct. Brucite, Mg(OH) 2 Gibbsite, Al(OH) 3

H-bonds 1:1 Phyllosilicates tet oct Sheets } 1:1 layer Kaolinite and Serpentine

Kaolinite: Al 2 Si 2 O 5 (OH) 4 - dioctahedral, 1:1 mineral

Sharing of Apical Oxygens in Tetrahdral Sheet with Hydroxyls of Two Octahedral Sheets tet oct tet Talc (2:1 trioctahedral mineral)

Phlogopite: KMg 3 (AlSi 3 O 10 )(OH) 2 Biotite: KFe 3 (AlSi 3 O 10 )(OH) 2 Muscovite: KAl 2 (AlSi 3 O 10 )(OH) 2 Micas tet oct tet oct tet K+K+ K+K+ K+K+ Unit layer of charge

K+K+K+K+

Si 6 O 18 Ditrigonal (hexagonal) Cavity

Illite (hydrous mica) Vermiculite Smectite Expandable 2:1 Layer Phyllosilicates tet oct tet oct tet K+K+ H2OH2O Ca 2+ H2OH2O H2OH2O Illite:  KAl 1.3 Fe 0.4 Mg 0.2 Si 3.4 Al 0.6 O 10 (OH) 2

Vermiculite dioctahedral:  Na x (Al,Fe) 2 (Si 4-x Al x )O 10 (OH) 2 n H 2 O trioctahedral:  Na x (Mg,Fe) 3 (Si 4-x Al x )O 10 (OH) 2 n H 2 O Expandable 2:1 Layer Phyllosilicates tet oct tet oct tet K+K+ H2OH2O Ca 2+ H2OH2O H2OH2O

Expandable 2:1 Layer Phyllosilicates Smectite Dioctahedral Forms: Montmorillonite  Na x (Al 2-x Mg x )Si 4 O 10 (OH) 2 Beidellite:  Na x (Al 2 )(Al x Si 4-x )O 10 (OH) 2 Trioctahedral Forms: Saponite:  Na x-y (Mg 3-y Al y ) 3 (Si 4-x Al x )O 10 (OH) 2 Hectorite:  Na x (Mg 3-x Li x ) 3 Si 4 O 10 (OH) 2

Interlayer Expansion Two Dominant Factors: 1. Structural Charge 2. Interlayer Ion

[Mg 2 Al 1 (OH ) 6 ]Mg 3 (Si 3 Al)O 10 (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 tet oct tet oct tet [Mg 2 Al 1 (OH ) 6 ]Mg 3 (Si 3 Al)O 10 (OH) 2

Iron Oxides Aluminum Oxides Manganese Oxides Accessory Minerals

Andisol - volcanic ash Hydrous Silicates and Aluminosilicates Accessory Minerals

Hydrous Silicates and Aluminosilicates Accessory Minerals 100 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

X-ray Diffraction: Foundation Consider wave properties

X-ray Diffraction: Foundation Constructive versus Destructive Interference

X-ray Diffraction: Foundation Bragg’s Law: n = 2d sin   d  wavelength   to 2.5 Å)

General Classes (layer build-up) of Phyllosilicate Minerals

Trioctahedral Phyllosilicate Minerals Sheets Octahedral Layer Only: Brucite, Mg(OH) 2 Oct. 1:1 Mineral: Serpentine, Mg 3 Si 2 O 5 (OH) 4 Tet. Oct. Tet. Oct. Tet. 2:1 Mineral: Talc, Mg 3 Si 4 O 10 (OH) 2 Layer Build-up: z y

MineralMg 2+ K+K+ Glycerol550 C Kaolinite777- Mica10 Vermiculite Smectite HIV HIS XRD: Chemical Treatment d-spacing, Angstroms

Octahedral Minerals Oct. Brucite, Mg(OH) 2 Gibbsite, Al(OH) 3

Serpentine: Mg 3 Si 2 O 5 (OH) 4 - trioctahedral Kaolinite: Al 2 Si 2 O 5 (OH) 4 - dioctahedral

Phlogopite: KMg 3 (AlSi 3 O 10 )(OH) 2 Biotite: KFe 3 (AlSi 3 O 10 )(OH) 2 Muscovite: KAl 2 (AlSi 3 O 10 )(OH) 2 Micas tet oct tet oct tet K+K+ K+K+ K+K+

Illite Vermiculite Smectite Expandable 2:1 Layer Phyllosilicates tet oct tet oct tet K+K+ H2OH2O Ca 2+ H2OH2O H2OH2O

oct (b) 2:1:1 Layer Phyllosilicates Hydroxy Interlayer Vermiculite (HIV) Hydroxy Interlayer Smectite (HIS) - pedogenic chlorites versus true chlorites tet oct tet oct tet [Mg 2 Al 1 (OH ) 6 ]Mg 3 (Si 3 Al)O 10 (OH) 2