Plagioclase plus pyroxene or hornblende could be found in which igneous rock?

Plagioclase plus pyroxene or hornblende could be found in which igneous rock?

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

Answer: (B)

Plagioclase with a dark ferromagnesian mineral such as pyroxene or hornblende signals an intermediate silica content in the rock. The rock that most consistently shows this exact mineral pairing in a volcanic, fine- to medium-grained form is andesite, the extrusion counterpart to diorite. Diorite would share the same minerals but is coarse-grained and forms underground; granite is felsic and lacks these dark minerals, and basalt is mafic and, while it can contain plagioclase and pyroxene, the described hornblende-pyroxene pairing fits andesite best in this set.

Plagioclase with a dark ferromagnesian mineral such as pyroxene or hornblende signals an intermediate silica content in the rock. The rock that most consistently shows this exact mineral pairing in a volcanic, fine- to medium-grained form is andesite, the extrusion counterpart to diorite. Diorite would share the same minerals but is coarse-grained and forms underground; granite is felsic and lacks these dark minerals, and basalt is mafic and, while it can contain plagioclase and pyroxene, the described hornblende-pyroxene pairing fits andesite best in this set.