This article describes a series of research done on the mineralogy of Canadian soils by the author and his colleagues over the past 35 years. During the period, 1962-77, the research was devoted to the characterization of minerals in soils and sediments with continuing effort to improve analytical methods for mineral identification and characterization. Of the research, a major difference in the clay mineral composition of the western prairie soil and eastern maritime soils was highlighted here. The prairie soils are smectitic, whereas the maritime soils are micaceous. It was noted, however, that potassium available to plants is always sufficient in the prairie soils but not in the maritime soils, although both soils have similar K2O content (∼3%). This is obviously reflected in the smectitic composition of the prairie soils. The composition includes smectite and vermiculite component layers as interstratified minerals, all of which can release K relatively easily than illites in the maritime soils as discrete or/and interstratified minerals. In the following 10 years from 1978-87, the research focused on various interactions of clay minerals with soil organic matter and inorganic compounds, as well as on the detection of poorly crystalline inorganic components in soils. Expandable clay minerals such as smectite can adsorb water-soluble soil organic matter between the layers only under low pH conditions, because under these conditions the majority of soil organic matter molecules are relatively undissociated and mostly remain neutral. At higher pH, the molecules dissociate negatively. This illustrates the importance of pH-dependent charge in the soil system. Oxide, oxyhydroxide, and hydroxide minerals occurring in soils also possess pH-dependent charge, thus they react as positively or negatively charged particles depending upon pH, unlike clay minerals which are permanently negatively charged. In the soil system, recognizing the presence of these charges is very important to understand reactions between minerals, organic matter, metal ions, and agrochemicals. The direction of research further shifted to make mineralogy interact with other domains of science in the last 10 years. This produced research work on mineralogy in a microenvironment rhizosphere, mineral grains as architectural materials for housing soil living habitats and a mineralogical database of Canadian soils. The role of minerals in soils is very diverse. Minerals release major and minor elements, adsorb water, and react with organic and inorganic compounds, and these actions are environmentally favourable and adverse as well. Mineral particles of appropriate sizes are apparently effective for protecting microbes by retarding decomposition of organic matter. Clay minerals, in particular, provide with large surfaces to promote reactions and interactions that play an important role in soil forming processes. Undoubtedly mineralogy will make a significant contribution to a better understanding of very complicated soil environments that have a great impact on the well-being of humankind.
