Rocks formed through cementation of accumulated materials under water is ?

Step 1: Analyze the question The question asks which type of rock forms when materials pile up under water and are then cemented together.

Step 2: Key concept Rocks are classified into three main groups by how they form:

• Igneous rocks form when molten magma or lava cools and solidifies (e.g., granite, basalt).
• Sedimentary rocks form when sediments (sand, mud, shells, plant remains) are deposited, usually in layers under water, then compacted and cemented over time (e.g., sandstone, limestone, shale, clay).
• Metamorphic rocks form when existing rocks are changed by heat and pressure (e.g., marble from limestone, slate from shale).

Step 3: Apply to the options

• A. Metamorphic: formed by heat and pressure, not cementation. ✗
• B. Igneous: formed by cooling of molten material. ✗
• C. Sedimentary: formed by accumulation, compaction and cementation of materials, typically under water. ✓
• D. Acidic: this describes the silica content of some igneous rocks (e.g., granite), not a rock type by formation. ✗

Step 4: Answer The correct option is C. sedimentary.

Exam tip: Remember "Sediment = Settle". Sedimentary rocks come from materials that settle in layers (strata) and often contain fossils. If a question mentions layers, fossils, deposition, or cementation, think sedimentary. In Nigeria, the sedimentary rocks of the Niger Delta and the Chad Basin are good examples, and they are where petroleum is found.