limestone - a sedimentary rock consisting mainly of calcium that was deposited by the remains of marine animalsatomic number 20, Ca, calcium - 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 atomic number 6, carbon, C - an abundant nonmetallic tetravalent element occurring in three allotropic forms: amorphous carbon and graphite and diamond; occurs in all organic compounds rock, stone - material consisting of the aggregate of minerals like those making up the Earth's crust; "that mountain is solid rock"; "stone is abundant in New England and there are many quarries" calcite - a common mineral consisting of crystallized calcium carbonate; a major constituent of limestone rottenstone, tripoli - a weathered and decomposed siliceous limestone; in powdered form it is used in polishing |