Plagioclase, quartz, biotite and hornblende would most likely be found in which rock type?

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Study for the ASBOG Fundamentals of Geology exam. Access flashcards, multiple-choice questions, and understand key geologic principles. Prepare confidently for your exam!

Multiple Choice

Plagioclase, quartz, biotite and hornblende would most likely be found in which rock type?

Explanation:
Mineral make-up guides igneous rock types: a combination of plagioclase with quartz plus amphibole (hornblende) and biotite points to an intermediate to felsic composition typical of dacite. Basalt and gabbro are mafic and usually lack quartz, favoring pyroxene and calcium-rich plagioclase. Granite is felsic and rich in alkali feldspar with quartz, but hornblende and biotite aren’t defining features there. Dacite commonly contains plagioclase, quartz (often present in these rocks), and hornblende and/or biotite, matching the minerals listed.

Mineral make-up guides igneous rock types: a combination of plagioclase with quartz plus amphibole (hornblende) and biotite points to an intermediate to felsic composition typical of dacite. Basalt and gabbro are mafic and usually lack quartz, favoring pyroxene and calcium-rich plagioclase. Granite is felsic and rich in alkali feldspar with quartz, but hornblende and biotite aren’t defining features there. Dacite commonly contains plagioclase, quartz (often present in these rocks), and hornblende and/or biotite, matching the minerals listed.

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