Here's why:
* Source material: Limestone is primarily formed from the accumulation of calcium carbonate (CaCO3) derived from marine organisms like corals, algae, mollusks, and foraminifera. These organisms use calcium carbonate to build their skeletons and shells.
* Compaction and Cementation: Over time, the skeletal fragments and shells accumulate and are buried under layers of sediment. The weight of the overlying sediment compresses the material, forcing out water and compacting the fragments together. Dissolved minerals in the water, like calcite (another form of CaCO3), act as cement, binding the fragments into a solid rock.
While other sedimentary rocks might contain some shell fragments, limestone is specifically defined by its high content of biogenic calcium carbonate, which originates from the remains of marine organisms.
