noun
: a salt CaCO 3 found in nature as calcite (as in limestone, chalk, and marble) and aragonite and in plant ashes, in bones, and in many shells, obtained also as a white precipitate by passing carbon dioxide into a suspension of calcium hydroxide in water, and used chiefly as a pigment, pigment extender, and filler, in dentifrices and pharmaceuticals especially as an antacid, and in making lime and portland cement — compare chalk 1, limestone , whiting II 2