Which igneous texture indicates coarse-grained rocks formed from slow cooling underground?

• A. Aphanitic texture indicates coarse-grained rocks formed from slow cooling underground.
• B. Obsidian texture indicates coarse crystals formed from rapid cooling deep underground.
• C. Phaneritic texture indicates coarse-grained rocks formed from slow cooling underground.
• D. Porphyritic texture indicates two-stage cooling with larger crystals in a finer groundmass.

Answer: (C)

Coarse grains form when magma cools slowly underground, giving crystals time to grow large. This slow, subterranean cooling produces a phaneritic texture, where the crystals are visible to the naked eye and roughly uniform in size. In contrast, rapid cooling near the surface creates aphanitic textures with tiny crystals, obsidian is glassy with no crystals due to very rapid cooling, and porphyritic textures show two-stage cooling with larger crystals embedded in a finer groundmass. So, the texture that indicates coarse-grained rocks formed from slow cooling underground is phaneritic.