We document stoichiometric dolomite occurring in a nonsaline Quaternary soil on the Kohala peninsula, northwestern Hawaii. Geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind-blown dust. The strontium isotopic composition of the dolomite (87Sr/87Sr = 0.7045–0.7048) is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater. Infiltration of soil waters with elevated Mg/Ca (>1) derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early-precipitated soil calcite and/or to direct dolomite precipitation in the profile. This demonstrates that well-ordered dolomite can form in a nonmarine environment at temperatures <100 °C without undergoing burial diagenesis.