What is the intrusive rock with a coarse grain that shares mineral composition with basaltic extrusive rocks?

What is the intrusive rock with a coarse grain that shares mineral composition with basaltic extrusive rocks?

• A. Granite
• B. Diorite
• C. Gabbro
• D. Peridotite

Answer: (C)

Focusing on texture and mineral makeup helps connect intrusive and extrusive rocks. Basalt is a mafic extrusive rock, meaning it cools quickly at the surface and forms a fine-grained texture, with minerals like calcium-rich plagioclase and pyroxene (and sometimes olivine). The plutonic, or intrusive, counterpart that shares this same basaltic mineralogy but cools slowly underground to form a coarse-grained texture is gabbro. So the best choice is the intrusive rock that matches basalt in composition and has large crystals due to slow cooling. Granite is felsic, diorite is intermediate, and peridotite is ultramafic, so they don’t fit basalt’s composition as well.

Focusing on texture and mineral makeup helps connect intrusive and extrusive rocks. Basalt is a mafic extrusive rock, meaning it cools quickly at the surface and forms a fine-grained texture, with minerals like calcium-rich plagioclase and pyroxene (and sometimes olivine). The plutonic, or intrusive, counterpart that shares this same basaltic mineralogy but cools slowly underground to form a coarse-grained texture is gabbro. So the best choice is the intrusive rock that matches basalt in composition and has large crystals due to slow cooling. Granite is felsic, diorite is intermediate, and peridotite is ultramafic, so they don’t fit basalt’s composition as well.