This article focuses on the use of two calcined marlstones as supplementary cementitious materials, one with palygorskite and smectite (MS1) as clay phases and the other with smectite only (MS2). The calcination and the reactivity of these two materials were first analysed by X-ray diffraction (XRD) and Magic Angle Spinning Solid State Nuclear Magnetic Resonance (MAS NMR). The two calcined marlstones were combined with Portland cement to produce mortars and measure compressive strength. The XRD and Al-27 MAS NMR results showed that 800 degrees C is an optimal calcination temperature and that both calcined marlstones can be used as supplementary cementitious materials. The reactivity of MS1 was found to be higher than that of MS2. This was confirmed with compressive strength measurements which showed superior performance for mortars blended with calcined MS1 rather than calcined MS2. This difference between MS1 and MS2 is due to the presence of palygorskite in MS1, which greatly improves the reactivity and final mechanical performances. Therefore, palygorskite bearing marlstones are suitable for a use as SCM and this suggests that palygorskite exhibits a significant pozzolanic reactivity.