Which Rocks term is correctly associated with identifying feature: “glassy texture with conchoidal fracture”, and also with “historically used for sharp cutting tools”?

Correct Answer: Option C — Obsidian. Obsidian is correct because it is glassy texture with conchoidal fracture. Obsidian is also associated with historically used for sharp cutting tools. A further identifying fact is that Obsidian is glassy texture with conchoidal fracture. Another useful fact is that Obsidian is associated with historically used for sharp cutting tools. Why the other options are incorrect: Option A — Sandstone: It is often shows bedding layers and is associated with commonly used as a building stone; those are the identifying facts of Sandstone. Option B — Limestone: It is reacts with dilute acid and is associated with a major raw material for cement; those are the identifying facts of Limestone. Option D — Shale: It is splits into thin layers called fissility and is associated with can metamorphose into slate; those are the identifying facts of Shale. Exam Takeaway: Link Obsidian with “glassy texture with conchoidal fracture” and “historically used for sharp cutting tools” for quick revision.