Final answer:
On the flanks of a volcano, aphanitic textured rocks, which are fine-grained and indicative of rapid cooling, are commonly found. This includes rocks such as basalt and rhyolite.
Step-by-step explanation:
On the flanks of a volcano, you are likely to find rocks with an aphanitic texture. This texture, also referred to as fine-grained, is indicative of extrusive or volcanic igneous rocks that cooled rapidly on the Earth's surface. You can distinguish this aphanitic texture because the mineral grains are too small to be seen without magnification. In contrast, pegmatitic texture is characterized by very large crystals and forms in late stages of magma cooling, pumice texture indicates a frothy, vesicular structure due to trapped gas bubbles, and rocks with a phaneritic texture have visible mineral grains because they cooled slowly inside the Earth and are therefore intrusive or plutonic.
When examining igneous rock samples for texture, such as on the flanks of a volcano, rocks with an aphanitic texture like basalt and rhyolite are commonly found. For instance, rhyolite is a felsic extrusive igneous rock with an aphanitic texture due to the rapid cooling of high-viscosity lava, often found in volcanic environments.