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.
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO 3). Glass making, in some circumstances, uses limestone. 2  It is added to toothpaste, paper, plastics, paint, tiles, and other materials as both white pigment and a cheap filler. 3  It can suppress methane explosions in underground coal mines. 4  Purified, it is added to bread and cereals as a source of calcium.