Colloid dispersion, through its role in soil science, hydrology, and contaminant transport, is a basic component of many natural resources and environmental education programs. However, comprehension of colloid dispersion phenomena is limited by the numerous variables involved. This article demonstrates how the Quirk-Schofield diagram can be used as a pedagogical tool to explain the relationship between colloid dispersion and three key variables: ionic strength, counterion valence, and pH. The theory of colloid dispersion is briefly reviewed, in order to provide the background needed to define the Quirk-Schofield diagram. These diagrams are then employed to qualitatively explain numerous published observations of environmental colloid dispersion, first in the case of constant pH and then in the case of variable pH. In addition, new Quirk-Schofield diagrams are presented for three common clay minerals: kaolinite, illite, and montmorillonite. These diagrams are used for quantitative analysis of two key studies from the literature on colloid-associated contaminant transport. The generality and simplicity of Quirk-Schofield diagrams, which provide a single framework to conceptualize many phenomena, should greatly assist student learning. (Contains 11 figures and 1 table.)