Calcined clays are widely used in blended cements to lower the carbon footprint associated with concrete industry. In the field, raw clays are often associated with iron impurities that may affect the properties of calcined clay. The present study investigates the influence of iron contaminated kaolinite clays on reactivity of limestone calcined clay cement. Natural and model clays with iron content varying from 5 to 22% were used. Clays were calcined in laboratory muffle furnace at two different temperatures of 750 and 850 °C. All iron rich clays satisfied the minimum reactivity benchmarks to be classified as a pozzolan according to lime reactivity test. The standard mortar compressive strength of LC3 prepared with each clay was evaluated at 3, 7, and 28 days. The strength values observed with blends made with natural clays remained in similar range. The behavior of model clays was found to be somewhat different as reactivity and strength values increased with the presence of iron impurity. The maximum strength gain was observed for kaolinitic clays with 12.5% iron content. It can be concluded from the study that low grade kaolinite clay with iron impurity up to 22% can be used for LC3 production based on their availability.