Next you must determine which of the four possibilities in the phaneritic row the rock corresponds to. To do this you need to determine what it's mineral composition is. Look for clues like the color, luster, cleavage, striations and shapes of different minerals in the rock. Considering it's mineral composition, determine which is the correct name for this rock on the phaneritic row of the table. Drag the rock to the proper box on the table.
Most glassy rocks are of rhyolitic composition and are called obsidian .
Rhyolitic rocks form glassy textures more commonly than basaltic rocks because they are more viscous and their crystals grow more slowly. Now, try the same procedure with another rock. Rhyolite text will go here. Such particular rock is of rhyolitic composition. This is where the andesite text will go.