Final answer:
Rhyolite, andesite, basalt, and obsidian are all classified as igneous and extrusive due to their formation from the rapid cooling of lava at the Earth's surface, resulting in a fine-grained or glassy texture.
Step-by-step explanation:
Rhyolite, andesite, basalt, and obsidian are all rocks that are classified as igneous and extrusive. These types of rocks form when magma, the hot molten liquid inside the Earth, erupts as lava and solidifies quickly at the surface. As a result, they tend to have a fine-grained or glassy texture due to the rapid cooling that doesn't allow large crystals to form. However, the composition of these rocks can vary from felsic, as in rhyolite, which is rich in lighter minerals like quartz and feldspar, to mafic in basalt, which contains more magnesium and iron. Obsidian is recognized by its glassy texture because it cools so rapidly that no crystals have time to form.