Cement slurries, cured cements, and methods of making cured cement and methods of using cement slurries are provided. The cement slurries have, among other attributes, increased yield point, reduced density, improved mechanical properties, increased resistance to H2S, and may be used, for instance, in the oil and gas drilling industry. The cement slurry comprises cement precursor material, Saudi Arabian volcanic ash, and an aqueous solution. The Saudi Arabian volcanic ash comprises SO3, CaO, SiO2, Al2O3, Fe2O3, MgO, and K2O and the cement slurry is free of any other SiO2 additive.