silicates.pdf
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Stage II Mineralogy DM Sherman, University of Bristol 2001/2002 Copyright 2001 DMSherman All rights reserved. Page 1 Sheet Silicates: Clay Minerals and Others.. Mineralogy Stage II University of Bristol Phyllosilicate Building Blocks Tetrahedral Layer (Si 6+x Al 2-x O 20 ) 10-
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Transcript of silicates.pdf
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Stage II MineralogyDM Sherman, University of Bristol
2001/2002
Copyright 2001 DMSherman All rights reserved. Page 1
Sheet Silicates:Clay Minerals and Others..
Mineralogy Stage IIUniversity of Bristol
Phyllosilicate Building BlocksTetrahedral Layer (Si6+xAl2-xO20)10-
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Stage II MineralogyDM Sherman, University of Bristol
2001/2002
Copyright 2001 DMSherman All rights reserved. Page 2
Phyllosilicate Building Blocks..
Octahedral Layer
Overview of Phyllosilicate Structures
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Stage II MineralogyDM Sherman, University of Bristol
2001/2002
Copyright 2001 DMSherman All rights reserved. Page 3
Kaolinite Al2Si2O5(OH)4
1:1 Phyllosilicate withlayers held together byhydrogen bonds.
Major alterationproduct of feldspars.
Mineral of China Clayin Cornwall.
Antigorite Mg3Si2O5(OH)4
Mg analogue of kaolinite.
One of three phases ofserpentine.
Alteration product ofolivine and other maficminerals.
Fe2+ end-member isgreenalite found in BIFs.
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Stage II MineralogyDM Sherman, University of Bristol
2001/2002
Copyright 2001 DMSherman All rights reserved. Page 4
The Serpentine PhasesMg3Si2O5(OH)4
Antigorite, Lizardite and Chrysotile.
Alteration product of olivine
2Mg2SiO4 + 3H2O -> Mg3Si2O5(OH)4 + Mg(OH)2
Crysotile (Asbestiform) Antigorite
Talc Mg6Si8O20(OH)4
2:1 Phyllosilicate withlayers held together byvan der Waals bonds.
Major alterationproduct of maficminerals at higher T.
Fe2+ end-member isminnesotaite found inBIFs.
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Stage II MineralogyDM Sherman, University of Bristol
2001/2002
Copyright 2001 DMSherman All rights reserved. Page 5
Pyrophyllite Al4Si8O20(OH)4
Al analogue of talc.
2:1 Phyllosilicate withlayers held together byvan der Waals bonds.
Alteration product ofmicas and feldspars.
Not very common...
Nature of Clay Minerals
Based on sheet silicate structure
Small particle (crystallite) size ( < 0.5 micron).
Alteration product of high-T minerals.
Major component of soils and sediments.
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Stage II MineralogyDM Sherman, University of Bristol
2001/2002
Copyright 2001 DMSherman All rights reserved. Page 6
2:1 Phyllosilicate Clay Minerals
1:1 Phyllosilicate Clay Minerals
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Stage II MineralogyDM Sherman, University of Bristol
2001/2002
Copyright 2001 DMSherman All rights reserved. Page 7
Clay Compositions per O20(OH)4
Mineral InterlayerCations
OctahedralCations
TetrahedralCations
LayerCharge
CECmol/kg
muscovite K2 Al4 Al2Si6 -2 0illite K2-x (x ~.5) Al4 Al2-xSi6+x x-2 0.1-0.4vermiculite (Mg,Ca)0.6-0.9 (Fe,Al)4 Al1.5Si6.5 1.2-1.8 1-1.5
smectitesmontmorillonite (general)
Mn+(x+y)/n MgyAl4-y AlxSi8-x -(x+y) 0.8-1.2
montmorillonite (Wyoming)
Ca0.5 Mg0.5Fe3+0.5Al3
Al0.5Si7.5 -1.0
montmorillonite (Cheto)
Ca0.5 MgAl3 Si8 -1.0
beidellite (Na2,Ca)0.35 Al4 Al0.7Si7.3 -0.7nontronite (Na2,Ca)0.35 Fe4 Al0.7Si7.3 -0.7
Dioctahedral Structures
Clay Compositions per O20(OH)4Trioctahedral Structures
Mineral InterlayerCations
OctahedralCations
TetrahedralCations
LayerCharge
CEC
phlogopite-biotite
K2 (Fe,Mg)6 Al2Si6 -2 0
vermiculite (Mg,Ca)0.6-0.9 (Fe2+,Mg)6 Al2-xSi6+x 1.2-1.8 1-1.5smectites: saponite (Na2,Ca)0.35 Mg6 Al0.8Si7.2 -0.7
