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How is carbon stored in limestone and other carbonate rocks?

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A labeled diagram of the periodic table entry for carbon, showing its atomic number 6, symbol C, electron configuration, atomic weight range, solid physical state, hexagonal crystal structure, and weakly acidic oxide properties. Color coding and icons indicate it is a nonmetal, solid at room temperature, with hexagonal structure and weak acidity. — carbon Carbon and its properties.

Carbon is stored in limestone and other carbonate rocks primarily in the form of calcium carbonate ( $C a C O_{3}$ ), which is typically found as the mineral calcite or its polymorph, aragonite.123

This storage occurs through the geologic carbon cycle:

Weathering and Transport: Atmospheric carbon dioxide dissolves in water to form carbonic acid, which weathers rocks and transports bicarbonate ions ( $H C O_{3}^{-}$ ) to the ocean.4
Precipitation: In marine environments, these ions combine with calcium ions ( $C a^{2 +}$ ) to form solid calcium carbonate. This process is often driven by lime-secreting organisms and foraminifera that use the mineral to build their shells or skeletons.415
Lithification: Upon the death of these organisms, their remains accumulate on the ocean floor, where they undergo lithification to become sedimentary rock.54
Diagenesis and Metamorphism: Over time, these deposits may be altered through diagenesis or metamorphism, sometimes transforming into dolomite ( $C a M g [C O_{3}]_{2}$ ) or recrystallizing into marble.162

Additionally, modern carbon capture and storage technologies can accelerate this natural process by injecting pressurized $C O_{2}$ into porous rock strata, where it dissolves in groundwater to form stable carbonate minerals.7