Obsidian is produced from felsic lava, rich in the lighter elements such as silicon, oxygen, aluminum, sodium, and potassium. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows. These flows have a high content of silica, granting them a high viscosity. Obsidian is an "extrusive” rock, which means it is made from magma that erupted out of a volcano. If it was an igneous rock that formed from magma underground and did not erupt, it would have been called an "intrusive" rock.Igneous rocks formed when liquid magma or lava—magma that has emerged onto the surface of the Earth cooled and hardened. A metamorphic rock, on the other hand, began as a rock either a sedimentary, igneous, or even a different sort of metamorphic rock