Which type of igneous rock forms from slow cooling deep underground and has coarse mineral grains?

Which type of igneous rock forms from slow cooling deep underground and has coarse mineral grains?

• A. Extrusive
• B. Intrusive
• C. Felsic
• D. Basaltic

Answer: (B)

When magma cools, the rate at which it loses heat determines how big the crystals get. Slow cooling deep underground gives crystals plenty of time to grow, producing a coarse-grained texture that you can see with the naked eye. Rocks with this texture form underground and are called intrusive igneous rocks. They tend to have visible mineral grains and include examples like granite, diorite, and gabbro, depending on their mineral makeup. In contrast, rocks that erupt onto the surface cool rapidly, resulting in tiny crystals or glassy textures. The terms felsic or mafic describe composition, not cooling rate, and intrusive rocks can be felsic, intermediate, or mafic. But the key idea here is that slow underground cooling creates coarse grains, which identifies the rock as intrusive.

When magma cools, the rate at which it loses heat determines how big the crystals get. Slow cooling deep underground gives crystals plenty of time to grow, producing a coarse-grained texture that you can see with the naked eye. Rocks with this texture form underground and are called intrusive igneous rocks. They tend to have visible mineral grains and include examples like granite, diorite, and gabbro, depending on their mineral makeup.

In contrast, rocks that erupt onto the surface cool rapidly, resulting in tiny crystals or glassy textures. The terms felsic or mafic describe composition, not cooling rate, and intrusive rocks can be felsic, intermediate, or mafic. But the key idea here is that slow underground cooling creates coarse grains, which identifies the rock as intrusive.