A dacite is the volcanic equivalent to which plutonic rock?

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

Answer: (A)

When comparing igneous rocks, extrusive (volcanic) rocks and their intrusive (plutonic) counterparts share the same overall chemical composition and mineral assemblage, differing mainly in grain size due to cooling rate. Dacite is a felsic volcanic rock with a mineralogy dominated by plagioclase and quartz, with only minor K-feldspar. The plutonic rock that matches this composition and mineralogy, but forms underground with coarse grains, is granodiorite. Granodiorite contains quartz along with plagioclase and potassium feldspar, with a higher proportion of plagioclase than potassium feldspar, making it the coarse-grained, intrusive counterpart to dacite.

Diorite would be the volcanic counterpart to andesite, granite would correspond to rhyolite, and gabbro to basalt, so granodiorite best pairs with dacite in this framework.