Answer :
Final answer:
Limestone is primarily composed of calcium carbonate (CaCO3) and forms mainly from the remains of marine organisms, with at least 50% calcium carbonate required for its classification. Types of limestone vary, including fossiliferous limestone, chalk, and coquina, which have distinct organic compositions. Limestone is a significant sedimentary rock, popular in construction and other industries.
Explanation:
Limestone Composition and Formation
Limestone is a type of rock primarily composed of the mineral calcium carbonate (CaCO3). The majority of limestone is biogenic, meaning it forms from organic materials, particularly the shells and skeletal remains of marine organisms such as mollusks and crustaceans. In warm, shallow waters, these organisms flourish, and when they die, their remains accumulate on the ocean floor, compacting over time to form limestone.
Additionally, some limestone can contain traces of dolomite (CaMgCO3). For a rock to be classified as limestone, it must consist of at least 50% calcium carbonate. Limestone can also vary in type, including forms such as chalk, coquina, and fossiliferous limestone, each with distinct characteristics and compositions.
Key Characteristics of Limestone Types
- Fossiliferous Limestone: Contains visible fossils and is formed from accumulated biological materials.
- Chalk: Comprised mainly of microscopic shells from marine organisms known as coccolithophores.
- Coquina: Made primarily of loosely cemented shell fragments.
When limestone is exposed to dilute hydrochloric acid (HCl), it exhibits fizzing due to the reaction of calcium carbonate.
