Describe how sedimentary rocks form and name three common sedimentary rock types.

• A. They form from compacted sediments or chemical/biological precipitation; common types include sandstone (clastic), limestone (chemical/biochemical), coal (biochemical/organic).
• B. They form only in the ocean.
• C. They form by mantle convection.
• D. They form from crystallization of magma.

Answer: (A)

Sedimentary rocks form at or near the surface from materials that are deposited, become buried, and are compacted and cemented into solid rock. This can happen in several ways: loose sediments like sand or mud settle and are lithified, minerals can precipitate out of water and glue sediments together, or the remains of organisms accumulate and become lithified as biochemical/organic rocks. The big idea is accumulation and burial of material, not melting and solidifying from magma.

Three common sedimentary rock types illustrate these paths well. Sandstone is a clastic rock formed from cemented sand grains, often quartz, showing how fragments cement together. Limestone forms from calcium carbonate either by chemical precipitation from water or from accumulated shells and other organic remains, illustrating chemical/biochemical processes. Coal comes from plant material that accumulated in swampy environments, was buried, and transformed into a solid rock through biochemical/organic processes.

So the correct choice captures the depositional and lithification processes and names representative rock types—sandstone, limestone, and coal. Other statements describe processes that don’t produce sedimentary rocks (like formation exclusively in the ocean or formation by mantle convection or magma crystallization), which aren’t how sedimentary rocks form.