Cation-exchange capacities and specific surface areas of clay minerals

mineral cation-exchange capacity at pH 7 (milliequivalents per 100 grams) specific surface area (square metre per gram)

kaolinite 3–15 5–40

halloysite (hydrated) 40–50 1,100*

illite 10–40 10–100

chlorite 10–40 10–55

vermiculite 100–150 760*

smectite 80–120 40–800

palygorskite-sepiolite 3–20 40–180

allophane 30–135 2,200*

imogolite 20–30 1,540*

*Upper limit of estimated values.