Final answer:
Felsic magmas, rich in silica, are highly viscous and associated with violent volcanic eruptions, while mafic magmas are less viscous and less explosive.
Step-by-step explanation:
Felsic magmas are the most viscous due to their high silica content. This high viscosity inhibits the gases from escaping easily, leading to a buildup of pressure and explosive volcanic eruptions. Mafic magmas, in contrast, are less viscous and therefore tend to result in less explosive eruptions, as gases can escape more easily. When felsic lava cools, it forms rocks like granite and rhyolite, which are often light in color.
Mafic magmas result in rocks such as basalt and gabbro, which are typically darker due to their iron and magnesium content. Rocks such as rhyolite are indicative of high-viscosity magmas which can erupt explosively when under sufficient pressure. The classification of igneous rocks by mineral content and color helps to understand the behavior of the magma from which they are derived.