plaster of paris,
plaster any of several gypsum cements; a white powder (a form of calcium sulphate) that forms a paste when mixed with water and hardens into a solid; used in making molds and sculptures and casts for broken limbs
atomic number 20,
calcium,
ca a white metallic element that burns with a brilliant light; the fifth most abundant element in the earth's crust; an important component of most plants and animals