Obsidian Cliff
One land form in Yellowstone National park is Obsidian Cliff. This cliff is a cliff of obsidian, a type of igneous rock. This type of rock forms when molten rock cools so quickly that the atoms in the rock can not arrange themselves into a crystalline structure. Also like all igneous rocks it solidifies above the earths surface. Obsidian is usually black but it can be green, or brown, and rarely, but it can also be red, orange, yellow, or blue.Lastly this rock is usually smooth, and has an unvarying texture.