Calcium /ˈkælsiəm/ [lat. Calcis – lime; first obtained from slaked lime] – a chemical element belonging to the group of alkaline earth metals, designation Ca (lat. Calcium), at.n. 20 am. 40.08. K. – silvery-white, light metal; density 1540 kg/m3, liquid = 851°C. Among the elements common in the earth’s crust, it ranks 5th (after oxygen, silicon, aluminum and iron). Its main minerals are calcite (chalk, marble, limestone), anhydrite, gypsum, fluorite (plaque spar). K. is used as a reducing agent for many rare and refractory metals in pure metallic form. K. steel, bronze, etc. is also used as a deoxidizing agent for alloys and is part of antifriction materials. K. compounds (lime, cement, etc.) are widely used in construction.