Which of the following is an example of a sedimentary rock?

• A. Limestone
• B. Gneiss
• C. Marble
• D. Basalt

Answer: (A)

Sedimentary rocks form from sediments that settle out of water or air and are pressed and cemented over time. Limestone is a classic example because it’s mainly calcium carbonate that often comes from accumulated shells and skeletal remains of marine organisms or from chemical precipitation in watery environments, creating layered deposits that later become rock. The other options belong to different rock types: gneiss is formed under high heat and pressure as a metamorphic rock with banded minerals; marble is metamorphic and forms when limestone is recrystallized under heat and pressure; basalt is an igneous rock formed by the cooling of lava or magma, not by sediment deposition and lithification.