Which term refers to a coarse-grained intrusive igneous rock, where individual crystals are visible to the naked eye?

Which term refers to a coarse-grained intrusive igneous rock, where individual crystals are visible to the naked eye?

• A. Phaneritic
• B. Aphanitic
• C. Glassy
• D. Porphyritic

Answer: (A)

When magma cools slowly underground, crystals have time to grow large enough to be seen with the naked eye. This coarse-grained texture is called phaneritic, and it is characteristic of intrusive rocks like granite and diorite. The other textures describe different cooling histories: aphanitic indicates rapid surface cooling with microscopic grains; glassy means no crystals form at all; porphyritic has a mix of large crystals in a finer-grained groundmass. So the term that best fits a coarse-grained intrusive igneous rock with visible crystals is phaneritic.

When magma cools slowly underground, crystals have time to grow large enough to be seen with the naked eye. This coarse-grained texture is called phaneritic, and it is characteristic of intrusive rocks like granite and diorite. The other textures describe different cooling histories: aphanitic indicates rapid surface cooling with microscopic grains; glassy means no crystals form at all; porphyritic has a mix of large crystals in a finer-grained groundmass. So the term that best fits a coarse-grained intrusive igneous rock with visible crystals is phaneritic.