Si8Mg2Al2O20(OH)2(OH2). 4H2O (i) A fibrous clay mineral composed of two silica tetrahedral sheets and one aluminum and magnesium octahedral sheet that make up the 2:1 layer that occurs in strips. The strips that have an average width of two linked tetrahedral chains are linked at the edges forming tunnels where water molecules are held. Palygorskite is most common in soils of arid regions. Also referred to as attapulgite. (ii) A magnesium aluminum silicate clay used in fertilizer production, including conditioning of fertilizer products, and as a suspending agent in suspension fertilizers.