Mathematics. ( 1 of a topology or topological space) having the property that every subset is an open set. 2  defined only for an isolated set of points: a discrete variable. 3  using only arithmetic and algebra; not involving calculus: discrete methods.
limestone - a sedimentary rock consisting mainly of calcium that was deposited by the remains of marine animals. atomic 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.
Marble is a metamorphic rock made out of limestone. When limestone is subjected to tremendous pressure for a long time (like if limestone is buried under a lot of other rock or an ocean) it gets squashed into marble.