Chalk
Chalk, soft, white rock composed of calcium carbonate, CaCO3, a type of fine-grained, porous limestone containing the shells of minute marine animals. Widely used in lime and cement manufacture and as a fertilizer, chalk is also used in cosmetics, plastics, crayons, and oil paints.
See also: Calcite; Calcium carbonate.
Additional topics
21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Catherine de' Medici to Children's home