Limestone is the parent rock of marble. The word marble can be used to refer to both metamorphosed and unmetamorphosed limestone.

Limestone is an example of a carbonate sedimentary rock.

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Limestone is principally CaCO3, which is a compound. Because naturally occurring limestone is usually formed from sea shells and ocean bottom debris mixed together, naturally occurring limestone is usually a mixture. Naturally occurring limestone in caves in the form of stalactites and stalagmites can be much more nearly pure than limestone formed from former sea beds, but even these kinds of cave limestone generally contain some materials other than pure CaCO3.