Which rock type involves stratification?

Step 1: Analyze the question The question asks which rock type shows stratification, meaning the arrangement of material in layers or beds (strata).

Step 2: Explain the concept Rocks are grouped by how they form:

• Igneous rocks form when magma or lava cools and solidifies. They are crystalline and are not layered (e.g., granite, basalt).
• Sedimentary rocks form when sediments such as sand, silt, clay, and shells are deposited, compacted, and cemented over time. Each deposition period adds a new layer (bed), so the rock is stratified (e.g., sandstone, limestone, shale, clay).
• Metamorphic rocks form when existing rocks are changed by heat and pressure. They may show foliation (banding), but this is not true stratification (e.g., gneiss, schist, marble).
• Volcanic rocks are a type of igneous rock (extrusive), formed from cooled lava, so they are not stratified.

Step 3: Apply to the options

• A. Metamorphic: shows foliation, not true stratification.
• B. Sedimentary: formed in layers, so it is stratified. ✔
• C. Volcanic: formed from cooled lava, not layered.
• D. Igneous: formed from cooled magma, not layered.

Step 4: Answer The correct answer is B. Sedimentary.

Exam tip: Link the words: Sedimentary = Strata = Stratification. If you see "layers," "beds," or "fossils" in a question, think sedimentary. Also remember that sedimentary rocks are the ones most likely to contain fossils, which is another common WASSCE question.