Which one among the following rocks is not a sedimentary rock?

Question

Which one among the following rocks is not a sedimentary rock?

1. A. Shale
2. B. Limestone
3. C. Slate (Correct answer)
4. D. Sandstone

Correct Answer

Option C — Slate

Detailed Solution & Explanation

The correct answer is Slate.

Key Points

• Slate is a fine-grained metamorphic rock formed from shale or mudstone under low-grade metamorphic conditions (heat and pressure).
• Shale, limestone, and sandstone are sedimentary rocks formed by deposition and compaction of sediments.
• Metamorphic rocks are formed from existing rocks transformed by heat, pressure, or chemical processes.

Additional Information

• The three rock families: igneous (cooled magma or lava), sedimentary (deposition and compaction of sediments) and metamorphic (existing rock altered by heat and pressure).
• Learn the standard parent → metamorphic pairs, which is how this question is set: shale → slate, limestone → marble, sandstone → quartzite, granite → gneiss, coal → graphite, basalt → schist.
• Note the trap here: shale is sedimentary but slate, its metamorphosed form, is not — the two sit in the same options list precisely to catch that.
• Sedimentary rocks are the only family that commonly bears fossils, since heat and pressure destroy them during metamorphism.