Question

Which type of igneous rock is described by the given mineral composition with 30% potassium feldspar, 30% quartz, 25% plagioclase feldspar, 10% amphibole, and 5% biotite, and fine-grained texture?

a) Granite
b) Diorite
c) Rhyolite
d) Gabbro

Answer 1

The igneous rock with 30% potassium feldspar, 30% quartz, 25% plagioclase feldspar, 10% amphibole, 5% biotite, and fine-grained texture is rhyolite, an extrusive rock that cools quickly at the surface.

Step-by-step explanation:

The type of igneous rock described by the given mineral composition with 30% potassium feldspar, 30% quartz, 25% plagioclase feldspar, 10% amphibole, and 5% biotite, and fine-grained texture would be rhyolite. This rock type is characterized as an extrusive or volcanic rock, which means it solidified from lava at the surface and has a fine-grained texture. Rhyolite has the same chemical composition as granite, which is coarse-grained and forms from magma that cools slowly within the Earth's crust; however, rhyolite cools much more quickly at the surface, resulting in smaller crystal sizes. Therefore, the correct answer is c) Rhyolite.