Limestone is an example of which rock type?

Limestone is an example of which rock type?

• A. Biochemical sedimentary rock
• B. Clastic sedimentary rock
• C. Metamorphic rock
• D. Igneous rock

Answer: (A)

Limestone forms mainly from calcium carbonate that comes from the secretions and fragments of marine organisms like corals and shellfish. When these calcareous remains accumulate and are compacted and cemented together, they lithify into rock. That makes limestone a biochemical sedimentary rock, because its origin involves biological material that settles as sediment and then becomes rock. It isn’t clastic, since it isn’t built from cemented fragments of preexisting rocks; it isn’t metamorphic, because it hasn’t been transformed by high heat or pressure; and it isn’t igneous, because it didn’t crystallize from molten rock. (Some limestone can form by direct chemical precipitation, but the common classification is biochemical sedimentary.)

Limestone forms mainly from calcium carbonate that comes from the secretions and fragments of marine organisms like corals and shellfish. When these calcareous remains accumulate and are compacted and cemented together, they lithify into rock. That makes limestone a biochemical sedimentary rock, because its origin involves biological material that settles as sediment and then becomes rock. It isn’t clastic, since it isn’t built from cemented fragments of preexisting rocks; it isn’t metamorphic, because it hasn’t been transformed by high heat or pressure; and it isn’t igneous, because it didn’t crystallize from molten rock. (Some limestone can form by direct chemical precipitation, but the common classification is biochemical sedimentary.)