Common Igneous Rocks (Part 5)
Andesite
Andesite is an aphanitic, intermediate igneous rock. Larger, dark-colored crystals in this example of andesite are hornblende.
Andesite (Photograph by Parvinder Sethi)
Obsidian
Obsidian is a glassy igneous rock. Extremely rapid cooling of volcanic material prevents crystal development and creates this volcanic glass.
Obsidian (Photograph by Parvinder Sethi)