Samples were collected in a saprolite and soil profiles derived from the weathering of igneous pyroxenites at Mount Saint-Bruno, Quebec. Alternation of the disaggregated rock produces small amounts of < 2 μm material. The various minerals present in the pyroxenite–augite, plagioclases, olivine, and biotite–and their weathering products were separated and analyzed with a microprobe. All primary minerals are transformed into smectites identified as beidellites, montmorillonites, saponites, Fe–Mg smectites, and transition smectites. The microenvironment determines the nature of the secondary minerals.