noun.
A common crystalline form of natural calcium carbonate, CaCO3, that is the basic constituent of limestone, marble, and chalk.
The Century Dictionary and Cyclopedia
noun.
Native calcium carbonate, or carbonate of lime, one of the commonest of minerals.
the GNU version of the Collaborative International Dictionary of English
noun.
Calcium carbonate, or carbonate of lime. It is rhombohedral in its crystallization, and thus distinguished from aragonite. It includes common limestone, chalk, and marble. Called also calc-spar and calcareous spar.