While the two words are often used interchangeably to refer to especially prized soils in certain places (like parts of Champagne, Burgundy and the Loire Valley), the two are not exactly the same. Chalk is a type of limestone, but not all limestone is chalk. Limestone is a marine sedimentary rock made in part from marine skeletons that are high in calcium. Chalk, along with marl and marble, is a type of limestone. Chalk is soft and porous, so vine roots penetrate it easily.