Which Rocks term is correctly associated with rock classification: “a vesicular volcanic rock”, and also with “formed when gas-rich lava cools rapidly”?

Correct Answer: Option A — Pumice. Pumice is correct because it is a vesicular volcanic rock. Pumice is also associated with formed when gas-rich lava cools rapidly. A further identifying fact is that Pumice is so porous that some pieces can float on water. Another useful fact is that Pumice is associated with used as an abrasive and lightweight aggregate. Why the other options are incorrect: Option B — Obsidian: It is a volcanic glass and is associated with formed by extremely rapid cooling of silica-rich lava; those are the identifying facts of Obsidian. Option C — Sandstone: It is a clastic sedimentary rock and is associated with formed by compaction and cementation of sand grains; those are the identifying facts of Sandstone. Option D — Limestone: It is a sedimentary carbonate rock and is associated with commonly formed from calcium carbonate remains or precipitation; those are the identifying facts of Limestone. Exam Takeaway: Link Pumice with “a vesicular volcanic rock” and “formed when gas-rich lava cools rapidly” for quick revision.