The concrete industry faces an urgent need to identify new supplementary cementitious material (SCM) sources. One class of materials available in large volumes are basaltic materials, which are often stockpiled in landfills as a waste product from quarries and granule operations. Reactivity testing on some such materials has shown them to be inert. The thermal activation of basaltic fines, and their mixtures with fly ash and limestone was therefore evaluated in a furnace using different process variables. Physical and chemical characterization using X-ray diffraction, Fourier transform infrared spectroscopy, and electron microscopy was performed on the raw and thermally activated materials. The reactivity of the resulting materials was directly measured. Heating beyond 1300 °C and cooling results in complete amorphization for the tested materials and resulted in the highest reactivity. Thus, the activation of basaltic fines into SCMs is feasible, although optimization to reduce temperatures is needed.