Clay Mineral & Soil Consistency

Clay Mineralogy

• Crystalline structure of clay minerals
• Important due to water movement and management considerations

Soil Consistence

• Field method to relate another soil property to clay mineralogy

Building Blocks of Clay

• Silica-tetrahedron-four sides, four oxygen molecules and one Silica (Si)
• Alumunium Octahedron-eight sides. six oxygen molecules and one Aluminum.

Definitions

• Silica tetrahedral sheet : a single-thickness plane of joined silica tetrahedra. The Silica tetrahedra are joined together by shared oxygen atoms.
• Aluminum octahedral sheet : a single-thickness plane of joined aluminum octahedra. The aluminum octahedra are joined together by shared oxygen atoms.
• Layer : combination of sheets, e.g.1:1 or 2 : 1

1 : 1 Clay Mineral :

• Like an open face sandwich
• A silica tetrahedral sheet (bread) joined to an aluminum octahedral sheet (filling). These sheets are joined by shared oxygen atoms.
• The most common 1:1 clay mineral is kaolinite.
• Layers are held together strongly by hydrogen bonding.
• Water will cause much expansion (swelling) beetween the layers.

Hydrogen Bonding

2 : 1 Clay Minerals :

• Like a sandwich with two slices of bread
• A silica tetrahedral sheet (bread) joined to an aluminum octahedral sheet (filling) joined to a silica tetrahedral sheet (bread). These sheets are joined by shared oxygen atoms.
• The 2:1 clays can be broken into 2 groups
  
• Non-expansive
• Expansive