Illinois Turf Pesticide Practice Test

When clay is heated to high temperatures, water and bound hydroxyl groups are driven off, and the structure becomes more rigid. This heat-treated state makes the clay less prone to crumbling into smaller particles, producing a material described as calcined clay. The other options are names of natural clay minerals (bentonite, kaolinite, montmorillonite) that describe composition rather than the heat-altered state. So the best term for clay that has been heated to resist breakdown is calcined clay.