In soils, these materials include clay and organic matter particles. Soil CEC is measured in millequivalents per 100 grams of soil (meq/100g). A meq is the number of ions which total a specific quantity of electrical charges. Common soil cations include: calcium (Ca++), magnesium (Mg++), potassium (K+), ammonium (NH4+), hydrogen (H+) and sodium (Na+).

A physical quality which inheres in an environmental material by virtue of the material's ability to adsorb exchangeable cations.