What type of rock is formed from rock fragments, organic material, or chemical precipitation?

• A. Sedimentary
• B. Metamorphic
• C. Igneous
• D. Clastic

Answer: (A)

Sedimentary rocks are formed by deposition and lithification of material at the Earth’s surface. The description—rock fragments, organic material, or chemical precipitation—encapsulates the three main pathways to make sedimentary rocks: pieces of preexisting rocks that are broken down and cemented together (detrital or clastic), remains of plants or animals that accumulate and turn into rock (organic/biochemical), and minerals that come out of solution and precipitate to form rock (chemical). This broad formation process is what defines sedimentary rocks.

Metamorphic rocks come from existing rocks transformed by heat and pressure, not from deposition and lithification. Igneous rocks form when molten rock cools and crystallizes. While clastic rocks are a type of sedimentary rock formed from fragments, the overall description points to sedimentary rocks as the category that includes these formation pathways.