Answer :
Final answer:
Limestone is mainly composed of calcium carbonate derived from the remains of marine organisms, such as shells and coral. For a rock to be classified as limestone, it must contain at least 50% calcium carbonate, primarily in the form of calcite. This biogenic rock formation plays a vital role in the Earth's geology and ecology.
Explanation:
Limestone Composition
Limestone is primarily composed of calcium carbonate (CaCO3), which is a mineral that comes from the organic remains of marine organisms. Most limestone forms through biological processes, primarily from the shells and skeletons of marine life such as mollusks and coral. As these organisms die, their remains accumulate on the ocean floor and are compacted over time to create limestone.
Organic Materials in Limestone
The organic materials that make up limestone mainly include the hard parts of marine invertebrates, such as the shells of mollusks, coral fragments, and the calcium-rich components of plankton. These materials contribute to the rock's biogenic origin, as they form a significant part of its composition.
Mineral Characteristics
In order to classify a sedimentary rock as limestone, it must contain at least 50% calcium carbonate. The dominant mineral in limestone is calcite, with some types of limestone also containing dolomite (CaMg(CO3)2). Calcite is distinctive because it fizzes when in contact with dilute hydrochloric acid, a characteristic that further confirms its presence in limestone.
