302-pp24 - UNIVERSITY OF SOUTH ALABAMA GY 302:...

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GY 302: Crystallography & Mineralogy GY 302: Crystallography & Mineralogy UNIVERSITY OF SOUTH ALABAMA Lecture 24: Phyllosilicates 2 Serpentine and Clays Lecture 24: Phyllosilicates 2 Serpentine and Clays
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Last Time Phyllosilicates 1 General chemistry/structure Phyllosilicate classification Mica, chlorite and talc groups
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Phyllosilicate Minerals (excludes clays, serpentine groups, and others)
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Phyllosilicate Structure Phyllosilicate Structure (Mica) Si 4 O 10 4- cross sectional view
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Phyllosilicate Classification 1:1 Structure (kaolinite, serpentine halloysite, Chrysotile, allophane) 2:1 Structure (Most micas and clays) (Chlorite Group)
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Phyllosilicate Structure Perfect Basal Cleavage C-axis
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Today’s Agenda Phyllosilicates 2 1. Serpentine Group 2. Other Phyllosilicates 3. Clay Minerals (Chemistry, modes of analysis)
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More Phyllosilicate Minerals Mineral Formula System “Clay” Minerals Kaolinite Al 2 Si 2 O 5 (OH) 4 Triclinic ”Smectite” (Na,Ca) 0-3 (Al,Mg) 2 Si 4 O 10 (OH) 2 ·n(H 2 O) Monoclinic *Bentonite (Na,Ca) 0-3 (Al,Mg) 2 Si 4 O 10 (OH) 2 ·n(H 2 O) Monoclinic Illite (K,H 3 O)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 [(OH) 2 ·(H 2 O) Monoclinic Serpentine Group (17 minerals) ”Serpentine” (Mg, Fe, Ni) 3 Si 2 O 5 (OH) 4 Monoclinic Antigorite Mg 3 Si 2 O 5 (OH) 4 Monoclinic Chrysotile Mg 3 Si 2 O 5 (OH) 4 Monoclinic Other Phyllosilicates Stilpnomelane (series) ~K(Fe, Al) 10 Si 12 O 30 (OH) 2 Triclinic Prehnite (series) Ca 2 Al(AlSi 3 O 10 )(OH) 2 Orthorhombic Sepiolite Mg 4 Si 6 O 15 (OH) 2 ·6(H 2 O) Orthorhombic Garnierite (Ni,Mg) 4 Si 6 O 15 (OH) 2 ·6(H 2 O) Orthorhombic Apophylite KCa 4 (Si 4 O 10 ) 2 F·8(H 2 O) Tetragonal *Astrophyllite** K 2 Na(Fe ++ ,Mn) 7 Ti 2 Si 8 O 26 (OH) 4 Triclinic
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Phyllosilicates Si:O ratio = 2:5 (3 shared oxygens) Anion component: Si 4 O 10 -4 or Si 8 O 20 -8 With Al substitution: AlSi 3 O 10 -5 or Al 2 Si 2 O 10 -6 General Formula: XYAlSi 3 O 10 (OH) 2 X = K + , Na + , Li + , Ca 2+ Y = Fe 2+/3+ , Mg 2+ , Al 3+ , rarely Cr 3+ , Ni 3+ , Mn 3+ Example (“Smectite”): (Na,Ca) 0-3 (Al,Mg) 2 Si 4 O 10 (OH) 2 ·n(H 2 O)
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Phyllosilicate Structure Tetrahedral layers (mostly SiO 4 4- ) Octahedral layers (variable; Al/Mg/OH) Cation layers (K + , Mg 2+ , Na + etc.) also H 2 O (clays)
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Phyllosilicate Structure The octahedral layers are given specific names according to the nature of the “filling”.
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302-pp24 - UNIVERSITY OF SOUTH ALABAMA GY 302:...

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