English: This image depicts the crystal structure of kaolinite. White spheres are oxygen ions; yellow spheres are hydroxyl ions; blue spheres are aluminium ions; and black spheres are silicon ions. The structure is described as 1:1 or TO because each layer consists of a sheet of silicon in tetrahedral coordination with oxygen (a T sheet) bonded to a sheet of aluminium in octahedral coordination with oxygen or hydroxyl (an O sheet). The sheets are bonded via shared oxygen ions to form a layer, and layers are bonded to each other through hydrogen bonding of the hydroxyl on the outer face of the O sheet to oxygen on the outer face of the neighboring T sheet.