Given the decreasing supply of conventional supplementary cementitious/pozzolans (SCPMs) materials like fly ash (FA), granulated ground blastfurnace slag (GGBS), silica fume (SF), the search for alternative sources of SCPMs for cement and concrete is gaining momentum. This paper aims to present part of an extensive experimental research program conducted on the utilization of calcined clay (CC) as a cementitious/pozzolans material for cement mortar and concrete, with a focus on its properties, performance, durability, and environmental impact. The long-term survival of the construction sector depends on the development of locally produced natural pozzolans. Screening, grinding, classifying, and calcination were some of the preparations and treatments applied to the domestically mined raw clay from Nizwa locality (NZW) in Oman. After a water-curing, the blended mortar’s strength and durability characteristics were assessed. The findings show that the blended mixes’ flow diameter has somewhat decreased. The mortar’s density at the hardened state was unaffected by the NZW replacement, but its strength increased at 10% replacement before decreasing at higher substitution levels. In the meantime, a 1.8% weight increase was recorded when the modified mortar was exposed to 5% sulfuric acid, with strength losses ranging from 4% to 50%. A 2 to 2.5% mass loss and a considerable gain in strength occurred after exposure to a blend solution of 5% (sulphate + chloride).