Final answer:
Felsic magmas are more viscous due to a higher viscosity and volatiles, resulting in slower movement and thicker lava flows. Examples of felsic rocks include rhyolite and obsidian.
Step-by-step explanation:
Felsic magmas are more viscous due to a higher viscosity and volatiles. Viscosity is a measure of a fluid's resistance to flow, and felsic magmas have a higher silica content, which makes them more viscous. The high viscosity of felsic magmas results in slower movement and thicker lava flows.
For example, rhyolite is a felsic igneous rock that forms from the cooling of high-viscosity lava. It is often light gray to pinkish to somewhat reddish in color. The lava flows of rhyolite are highly viscous and appear as if they have flowed like oozing toothpaste.
Another example is obsidian, a type of volcanic glass that forms from felsic magma. It has a glassy texture and is formed when lava cools quickly with minimal crystal growth due to its high viscosity.