This is a fine example of obsidian igneous rock (volcanic glass). It originates from an outcrop in the Rocky Mountains, but the exact locality is unknown. This is a nice example that has some sharp edges on it. This material was used by Indians and ancient humans to make projectile points, blades, and tools.
Refer to the photo. The black centimeter cube is shown for scale and is not included. You are purchasing the specimen shown. Your purchase will include an ID label.