Which statement about sedimentary rocks is correct?

• A. They form primarily through accumulation and compaction of sediments and remains.
• B. They are formed from solidification of molten magma.
• C. They form primarily through heat and pressure metamorphism.
• D. They form by melting existing rocks.

Answer: (A)

Sedimentary rocks form from sediments that are deposited, buried, and lithified. Particles settle from water or air, accumulate in layers, and are compacted by overlying weight and cemented by minerals that precipitate from groundwater. This lithification turns loose sediments into solid rock, and it can involve fragments from other rocks, organic remains, or minerals precipitated from solution. That’s why this statement best describes sedimentary rocks. The other descriptions refer to rocks formed by melting or by heat and pressure transforming existing rocks, which are processes for igneous and metamorphic rocks.