Cement is usually a mixture of :

Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most nonspecialty grout. It usually originates from limestone. It is a fine powder produced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time) and up to 5% minor constituents. Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates, the remainder consisting of aluminium- and iron-containing clinker phases and other compounds.