Another way to work this out is through the specific surface area of each mineral, since surface area and particle size move in opposite directions for the same amount of material.
Montmorillonite has the highest specific surface area of all common clay minerals, close to 700 to 800 square metres per gram, because its particles are the thinnest.
Illite has a much lower specific surface area, roughly 100 to 200 square metres per gram, since its particles are thicker than montmorillonite but still fairly fine.
Chlorite behaves similarly to illite in the field but is generally coarser, giving it a slightly lower specific surface area and hence a larger particle size.
Kaolinite has the lowest specific surface area among the four, often below 20 square metres per gram, because it forms the thickest, most stacked particles.
Ranking from the highest specific surface area, smallest particle, to the lowest specific surface area, largest particle, gives Montmorillonite, Illite, Chlorite, Kaolinite, the same increasing size order found before.
\[\boxed{\text{Montmorillonite, Illite, Chlorite, Kaolinite}}\]