While Obsidian Cliff (rising nearly 200 feet high from its base) might initially look like many other high rising cliffs in the park, it has a unique place in the history of this area extending back to prehistoric inhabitants of the park and early Native Americans that lived in or traveled through Yellowstone. Prized for its unique characteristics, this hard obsidian volcanic glass was chipped and formed by these early inhabitants to make arrowheads, spearheads, knife blades and other useful tools. In 1996, Obsidian Cliff became a National Historic Landmark.
Large boulders of obsidian are positioned at the base of the cliff and next to the road. During the afternoon of a sunny day, the obsidian volcanic glass cliff can intensely reflect the light. You are prohibited to enter the area or take pieces of obsidian. However, located relatively close to the cliff, and on the other side of the road, is a pull off with a kiosk that provides historical information about the cliff’s obsidian and its use by early inhabitants. It also has pieces of obsidian embedded in the display to be touched and felt.
Obsidian is a volcanic rock that cooled and hardened before mineral crystals could form, resulting in a rock texture that is glassy and somewhat translucent. The reason the obsidian cooled before crystals could form could be that it cooled quickly, lacked the dissolved water that facilitates crystal formation, or a combination of both.