What are sedimentary rocks?

• A. Rocks formed from solidification of molten magma.
• B. Rocks formed by accumulation of fossils in layers.
• C. Rocks formed by deep crust metamorphism.
• D. Rocks formed from accumulation and compaction of mineral and organic particles, often in layers.

Answer: (D)

Sedimentary rocks form from loose material that settles out of water or air, building up in successive layers, and then being squeezed and glued together over time. The key idea is that these rocks arise from accumulation and lithification of mineral grains and organic fragments, often in distinct layers called bedding. Weathering and erosion create the sediments, which are transported, deposited, and finally compacted under overlying weight and cemented by minerals precipitating from pore waters. This process can produce clastic rocks from fragments (like sandstone or shale), chemical rocks from minerals that precipitate (like rock salt), or organic rocks from accumulated plant or animal remains (like coal or some limestones). This is different from rocks formed by cooling molten magma (igneous) or rocks altered by high heat and pressure deep in the crust (metamorphic).