Gray Ordinary Portland Cement is the most commonly used type and is a high-quality, cost-effective building material composed mainly of clinker. White Portland Cement is produced with limestone, low iron kaolin clay, and gypsum for architectural works requiring brightness and artistic finishes. Masonry or mortar cement is mixed with finely ground limestone for uses like concrete blocks and brick work. Oil-well cement is a specially designed variety of hydraulic cement produced with gray Portland clinker for use in oil wells at high temperatures and pressures. Blended cements are produced by mixing Portland cement with materials like slag, fly ash, and lime to reduce CO2 emissions and offer more sustainable products.