Abstract: A process for treating a bentonite having a montmorillonite content of at least 85% which, when activated with sodium ions dried and ground, does not swell more than about 2.5-fold when gradually added to deionised water at room temperature and when crushed dried and calcined to an LoI of less than 4% at 190° C. absorbs 16 to 22% by weight of water in a controlled environment at 25° C. and a relative humidity of 40% by weight, which process comprises the following steps in the following order: i) drying to a moisture content from 25 to 35% by weight; ii) conditioning by crushing, mixing and/or extruding; iii) addition of water to form an extrudable paste having a moisture content of 25 to 40% by weight; iv) extrusion through a die preferably from 4 to 10 mm in diameter; v) drying to a moisture content from 10 to 14% by weight; vi) calcining at 120 to 250° C. to an LoI of less than 4% at 190° C.; and vii) reduction to particles.