What is Limestone? Limestone is a sedimentary rock composed
primarily of calcium carbonate (CaCO3) in the form of the
mineral calcite. It most commonly forms in clear, warm, shallow
marine waters. It is usually an organic sedimentary rock that
forms from the accumulation of shell, coral, algal and fecal
debris. It can also be a chemical sedimentary rock formed by the
precipitation of calcium carbonate from lake or ocean water.
Limestone-Forming Environment - Marine Most limestones form in
shallow, calm, warm marine waters. That type of environment is
where organisms capable of forming calcium carbonate shells and
skeletons can easily extract the needed ingredients from ocean
water. When these animals die their shell and skeletal debris
accumulate as a sediment that might be lithified into limestone.
Their waste products can also contribute to the sediment mass.
Limestones formed from this type of sediment are biological
sedimentary rocks. Their biological origin is often revealed in
the rock by the presence o