Which Rocks term is correctly associated with formation process: “formed by rapid cooling of lava at the surface”, and also with “dark-coloured and fine-grained”?

Correct Answer: Option B — Basalt. Basalt is correct because it is formed by rapid cooling of lava at the surface. Basalt is also associated with dark-coloured and fine-grained. A further identifying fact is that Basalt is dark-coloured and fine-grained. Another useful fact is that Basalt is associated with common in oceanic crust and lava plateaus. Why the other options are incorrect: Option A — Pumice: It is formed when gas-rich lava cools rapidly and is associated with so porous that some pieces can float on water; those are the identifying facts of Pumice. Option C — Obsidian: It is formed by extremely rapid cooling of silica-rich lava and is associated with glassy texture with conchoidal fracture; those are the identifying facts of Obsidian. Option D — Sandstone: It is formed by compaction and cementation of sand grains and is associated with often shows bedding layers; those are the identifying facts of Sandstone. Exam Takeaway: Link Basalt with “formed by rapid cooling of lava at the surface” and “dark-coloured and fine-grained” for quick revision.