NCFE Earth Science Practice Exam 2026 – The All-in-One Guide to Mastering Your Exam!

Limestone is primarily composed of calcite, which is a form of calcium carbonate (CaCO3). This mineral forms through both biological and chemical processes, often from the accumulation of the remains of marine organisms such as coral and shellfish, as well as through the precipitation of calcium carbonate from water. Its characteristics—such as a hardness of 3 on the Mohs scale and its ability to fizz in weak acids—help distinguish calcite as the dominant mineral in limestone. The formation of limestone plays an important role in various geological processes and the carbon cycle, impacting sedimentary rock formation and the storage of carbon dioxide in Earth's crust. Understanding the mineral composition of limestone is essential for various applications in geology, construction, and environmental science.

The other minerals listed do not represent the primary component of limestone, as quartz is a key constituent of other sedimentary rocks, feldspar is more common in igneous rocks, and gypsum is a distinct mineral associated with evaporite deposits.