Which texture is typical of intrusive igneous rocks?

Which texture is typical of intrusive igneous rocks?

• A. Coarse-grained
• B. Fine-grained
• C. Glassy
• D. Porphyritic

Answer: (A)

When magma crystallizes underground, it cools slowly, giving minerals time to grow into larger crystals. That slow cooling produces a coarse-grained texture, where mineral grains are big enough to see with the naked eye. This is typical of intrusive igneous rocks like granite and diorite. In contrast, rocks formed at the surface cool quickly and have fine-grained textures, or can be glassy, or show a mixture of large crystals in a fine matrix (porphyritic). So the coarse-grained texture best matches intrusive igneous rocks.

When magma crystallizes underground, it cools slowly, giving minerals time to grow into larger crystals. That slow cooling produces a coarse-grained texture, where mineral grains are big enough to see with the naked eye. This is typical of intrusive igneous rocks like granite and diorite. In contrast, rocks formed at the surface cool quickly and have fine-grained textures, or can be glassy, or show a mixture of large crystals in a fine matrix (porphyritic). So the coarse-grained texture best matches intrusive igneous rocks.