One of the most famous areas for rockhounding obsidian is Glass Buttes. Glass Buttes is situated in the High Lava Plains of central Oregon near Bend. The region consists of rhyolitic formations containing large amounts of obsidian. This area is a free for public digging. The two most prominent hills formed by eruption of a rhyolithic lava are Glass Butte and Little Glass Butte.
Obsidian is an igneous rock that has an amorphous structure. It is produced from rhyolite that is rich in silica and low in water. When this ryolith erupted, its temperature quickly drops below the temperature to create mineral crystals and a natural silica glass was formed. Black is the most abundant color in obsidian, and it is derived from oxidized magnetite contained within the silica. The presence of Hematite creates a red color, which often flows in bands to form mahogany obsidian. Patterns of gas bubbles can create sheens within the glass. When they are combined with oxidized chemical elements, they can produce an internal gloss, such as silver obsidian or an iridescence like rainbow obsidian.