Inorganic Soil Colloids
• Silicate clays (layer silicates):
– Kaolinite, Montmorillonite
– Vermiculite, Illite
• Oxide clays (Non-silicate clays) (sesquioxides):
– Fe oxide and hydrous oxide – Hematite, Goethite
– Al oxide and hydrous oxide – Gibbsite, Boehmite
• Amorphous clays:
– Allophane
– Imogolite

Silicate Clays (Layer silicates)
Basic structural units:
1. Silica tetrahedron 2. Alumina octahedron

Silica sheet
Octahedral sheet