building soil minerals. expected ion corrdination
TRANSCRIPT
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