Which option best describes the rock known as alkali feldspar-rich rock with minor mafic minerals?

Which option best describes the rock known as alkali feldspar-rich rock with minor mafic minerals?

• A. Basalt
• B. Trachyte
• C. Rhyolite
• D. Granodiorite

Answer: (B)

Trachyte is the rock type that fits an alkali feldspar–rich composition with only minor mafic minerals. In igneous rock naming, when alkali feldspar (potassium-rich feldspar) dominates and quartz is minimal or absent, the fine‑grained volcanic rock is described as trachytic. It typically has a light color and contains small amounts of dark minerals like biotite or hornblende, rather than the quartz- and plagioclase-rich textures you’d expect in other felsic rocks. Basalt is a mafic rock dominated by pyroxene and plagioclase, with little alkali feldspar. Rhyolite is felsic and quartz-rich, so quartz is a prominent mineral rather than the alkali feldspar dominance described. Granodiorite is a coarse-grained plutonic rock with substantial quartz and plagioclase, not dominated by alkali feldspar.

Trachyte is the rock type that fits an alkali feldspar–rich composition with only minor mafic minerals. In igneous rock naming, when alkali feldspar (potassium-rich feldspar) dominates and quartz is minimal or absent, the fine‑grained volcanic rock is described as trachytic. It typically has a light color and contains small amounts of dark minerals like biotite or hornblende, rather than the quartz- and plagioclase-rich textures you’d expect in other felsic rocks.

Basalt is a mafic rock dominated by pyroxene and plagioclase, with little alkali feldspar. Rhyolite is felsic and quartz-rich, so quartz is a prominent mineral rather than the alkali feldspar dominance described. Granodiorite is a coarse-grained plutonic rock with substantial quartz and plagioclase, not dominated by alkali feldspar.