Clay Mineralogy. Clay is a particle SIZE Predominant make-up is SECONDARY minerals. Minerals can be crystalline or amorphous. Example: SiO 2 crystalline QUARTZ (SiO 2 ) : resistant to weathering Amorphous silica (SiO 2 ) : 10x more soluble. Silicate Clays (crystalline)
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crystalline QUARTZ (SiO2): resistant to weathering
Amorphous silica (SiO2): 10x more soluble
Micelle: particle of silicate clay
Composed of tetrahedral and octahedral “sandwiches”
Tetrahedron: central cation (Si+4, Al+3) surrounded by 4 oxygens
Octahedron: central cation (Al+3,Fe+2, Mg+2) surrounded by 6 oxygens (or hydroxyls)
Connected tetrahedra, sharing oxygens
Connected octahedra, sharing oxygens or hydroxyls
Lower charge cations replace higher charge cations as central cation
Different types of silicate clays are composed of sandwiches (combinations) of layers with various substances in their interlayer space.
2:1 two tetrahedral sheets to one octahedral sheet
1:1 one tetrahedron sheet to one octahedral sheet
In dry soils, bonding force is strong and hard clods form; deep cracks
In wet soils, water is drawn into interlayer space and clay swells.