Which rock is an intrusive igneous rock?

Which rock is an intrusive igneous rock?

• A. Basalt
• B. Obsidian
• C. Andesite
• D. Granite

Answer: (D)

Intrusive igneous rocks form when magma cools slowly below the surface, allowing large crystals to grow. This slow cooling gives a coarse-grained texture where you can see the individual crystals. Granite fits this perfectly: it’s a light-colored, felsic rock with visible crystals of quartz and feldspar, formed underground. By contrast, basalt and andesite are typically formed from magma that erupts onto the surface and cools quickly, producing fine-grained rocks. Obsidian forms from very rapid cooling of lava into volcanic glass with no crystals. So granite is the one that crystallizes underground to create a coarse texture, making it the intrusive igneous rock.

Intrusive igneous rocks form when magma cools slowly below the surface, allowing large crystals to grow. This slow cooling gives a coarse-grained texture where you can see the individual crystals. Granite fits this perfectly: it’s a light-colored, felsic rock with visible crystals of quartz and feldspar, formed underground.

By contrast, basalt and andesite are typically formed from magma that erupts onto the surface and cools quickly, producing fine-grained rocks. Obsidian forms from very rapid cooling of lava into volcanic glass with no crystals. So granite is the one that crystallizes underground to create a coarse texture, making it the intrusive igneous rock.