Dacite would most likely contain which mineral assemblage?

Dacite would most likely contain which mineral assemblage?

• A. Plagioclase, quartz, biotite, and hornblende
• B. Olivine and pyroxene
• C. K-feldspar and quartz
• D. Calcite and dolomite

Answer: (A)

Dacite is an intermediate felsic volcanic rock with relatively high silica and typically contains quartz. A classic dacitic mineral mix includes plagioclase feldspar, quartz, and light-colored ferromagnesian minerals such as biotite and hornblende. This combination—plagioclase, quartz, biotite, and hornblende—best matches the expected dacite assemblage. Olivine and pyroxene are characteristic of more mafic rocks like basalt or gabbro, not dacite. K-feldspar with quartz points to a granitic-like composition such as rhyolite/granite, while calcite and dolomite are carbonate minerals not associated with igneous rocks like dacite.

Dacite is an intermediate felsic volcanic rock with relatively high silica and typically contains quartz. A classic dacitic mineral mix includes plagioclase feldspar, quartz, and light-colored ferromagnesian minerals such as biotite and hornblende. This combination—plagioclase, quartz, biotite, and hornblende—best matches the expected dacite assemblage. Olivine and pyroxene are characteristic of more mafic rocks like basalt or gabbro, not dacite. K-feldspar with quartz points to a granitic-like composition such as rhyolite/granite, while calcite and dolomite are carbonate minerals not associated with igneous rocks like dacite.